NIMP| Corneliu GHICA, Author at NIMP

Education

2001 - PhD in Physics: thin films growth, structure and properties

University of Bucharest, Faculty of Physics and Louis Pasteur University of Strasbourg, France

Thesis title: "Study of thin films deposited by laser ablation: manganites with colossal magnetoresistance effect"

PhD supervisors: Dr. Ion N. Mihailescu and Dr. Jean-Paul Deville

1995 - PhD in Physics: Optical engineering, optical spectroscopy and laser technologies

University of Bucharest, Faculty of Physics

1994 - BSc Physics: Optical engineering, optical spectroscopy and laser technologies

University of Bucharest, Faculty of Physics

Positions

Employer: National Institute of Materials Physics

Position: Scientific researcher I, Head of the Laboratory of Atomic Structures and Defects in Advanced Materials

Research interests

In-depth microstructural and analytical characterization of advanced materials, interfaces and extended defects using atomic-resolution techniques available in aberration-corrected transmission electron microscopy.
Quantitative HRTEM characterization of strain fields associated with extended defects and interfaces.
Assessing the structure-properties correlation in thin films and nanostructured functional materials by atomic-resolution techniques like HRTEM, STEM, EDS, EELS, in situ and operando experiments.

Expertize

Advanced user of electron microscopy techniques (TEM/HRTEM, SAED, EDS, EELS, STEM, EFTEM) and software for data processing and image simulation.

TEM specimen preparation (powders, thin films, ceramics) by mechanical grinding and ion milling.

Thin film deposition by PVD, PLD and sol-gel.

Projects

1. Nanoscaled ferroelectric (pseudo)-binary oxide thin film supercapacitors for flexible and ultrafast pulsed power electronics (NanOx4Estor)

Project Type: M-ERA.NET, Start Date: 2022-06-28 End Date: 2024-12-31

2. Interplay structure-functionality in the case of nanostructured materials for gas sensors by electron tomography and operando TEM

Project Type: Mobility, Start Date: 2019-07-01 End Date: 2020-12-15

3. From 2D to 3D+ nanoscale characterization of advanced functional materials

Project Type: PCE, Start Date: 2017-07-12 End Date: 2019-12-31

4. Atomically resolved structure and interface related phenomena in nano-scale modulated smart materials

Project Type: PCE, Start Date: 2013-09-02 End Date: 2015-11-30

5. Laser processing of defects induced in silicon by RF plasma hydrogenation. Contribution to the development of the SOI technology.

Project Type: PCE, Start Date: 2007-09-30 End Date: 2010-09-30

Publications

1. Low traces of acetone detection with WO3-based chemical sensors

Authors: Stanoiu, A; Vlaicu, ID; Iacoban, AC; Mihalcea, CG; Ghica, C; Florea, OG; Dinu, IV; Mercioniu, I; Simion, CE

Published: APR 1 2024, MATERIALS CHEMISTRY AND PHYSICS, 316, 129105, DOI: 10.1016/j.matchemphys.2024.129105

This work presents the ability of WO3-based sensors to detect low traces of acetone, specifically within the range of 0.25-5 ppm, specific to the in -field atmosphere. The WO3 powder was synthesised through the hydrothermal method. Morpho-structural investigations showed a monoclinic structure and a good crystallization of the WO3 powder, containing well -grown and faceted grains along low -index crystallographic planes. The paste obtained by mixing the powder with propanediol was screen -printed as a thick layer onto commercial alumina substrates, obtaining the chemical sensors. A dynamic computer -controlled Gas Mixing System was utilized to ensure controlled airflow with variable relative humidity and acetone concentrations. The sensor response was explained based on physico-chemical equations, taking into consideration pre -adsorbed species of oxygen and water, both of which are relevant constituents of atmospheric conditions. The results highlight the applicative potential of WO3, having a good signal-to-noise ratio in relative humidity conditions up to 90% and a pronounced sensitive selectivity to acetone.

2. In-depth insight into the structural properties of nanoparticulate NiO for CO sensing

Authors: Mihalcea, CG; Stefan, M; Ghica, C; Florea, OG; Stanoiu, A; Simion, CE; Somacescu, S; Ghica, D

Published: APR 1 2024, APPLIED SURFACE SCIENCE, 651, 159252, DOI: 10.1016/j.apsusc.2023.159252

The outstanding properties exhibited by the p-type NiO nanostructures can be greatly affected by morpho-structural and defect characteristics with constructive or competing effects. We have conducted an in-depth study on NiO nanoparticles obtained by hydrothermal synthesis and submitted to various thermal treatments, to monitor the evolution of their structural properties and the effect of the thermal history on their CO sensing. Correlated electron paramagnetic resonance and analytical transmission electron microscopy investigations evidenced an amount of up to 1 % metallic nickel clusters close to surface in the NiO nanoparticles calcined at 400 degrees C and 500 degrees C for 8 h. Subsequent annealing in vacuum and in air of the sample calcined at 400 degrees C resulted in different size distributions and morphology of the NiO nanoparticles and an increase/decrease of the nickel phase, respectively. Comparative CO sensing tests on the two pristine samples and on the sample calcined at 400 degrees C and further annealed in air at 500 degrees C for 2 h showed an increase in the baseline resistance of the later due to the decrease of free charge carriers induced by the dissolution of the nickel clusters. The overall CO sensing results show a strong dependence on the samples thermal history.

3. Phase transitions in ferroelectric ZrO₂ thin films

Authors: Pereira, RMP; Istrate, MC; Figueiras, FG; Lenzi, V; Silva, BM; Benamara, M; Romanyuk, KN; Ghica, C; Almeida, BG; Marques, L; Pereira, M; Silva, JPB

Published: MAR 15 2024, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 172, 108102, DOI: 10.1016/j.mssp.2023.108102

In this work, the formation of the orthorhombic phase of ZrO2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO2 through oxygen scavenging. The ferroelectric properties of the W/ZrO2/W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarizationvoltage measurements. A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie-Weiss temperature of 130 degrees C, significantly lower than the theoretical value for the bulk.

4. Unlocking superior NO₂ sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors

Authors: D'Olimpio, G; Boukhvalov, DW; Galstyan, V; Occhiuzzi, J; Vorochta, M; Amati, M; Milosz, Z; Gregoratti, L; Istrate, MC; Kuo, CN; Lue, CS; Ghica, C; Comini, E; Politano, A

Published: 2024 MAR 18 2024, JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d4ta01287a

To advance gas sensor technologies, it is essential to identify materials that exhibit both high selectivity and sensitivity. Here, we unravel the gas-sensing capabilities of indium sulfide (InS) nanosheets, particularly in relation to nitrogen dioxide (NO2) detection. Utilizing a synergistic approach that combines in situ and operando experimental methodologies with density functional theory calculations, we demonstrate that these nanosheets offer outstanding sensitivity toward NO2, characterized by a remarkably low detection threshold of 180 ppb at an operational temperature of 350 degrees C. This remarkable sensitivity is ascribed to the electronic charge redistribution around the Fermi level, facilitated by an oxygen-deficient In2O3-x surface layer that forms naturally when the InS surface is exposed to ambient conditions. A pivotal aspect of our investigation was the exploration of the influence of sulfur abstraction on these surface modifications. We demonstrate that sulfur abstraction plays a critical role in the formation and operational efficacy of the In2O3-x layer, thereby acting as a key element in the sensor mechanism. This unique surface chemistry not only amplifies the sensitivity to NO2 but also confers unparalleled selectivity over other gases and volatile organic compounds. Notably, this level of performance exceeds that of other 2D semiconductors and metal oxides, thus establishing InS nanosheets as an ideal platform for high-performance gas sensors suitable for demanding environments. Moreover, unlike many state-of-the-art sensor materials, InS-based sensors can withstand a wider variety of environmental conditions due to their superior water adsorption resistance.

5. Surface properties, chemical reactivity, and ambient stability of cadmium diarsenide CdAs2, a topological chiral material hosting Kramers-Weyl fermions

Authors: Zhang, YX; D'Olimpio, G; Bondino, F; Nappini, S; Istrate, MC; Sankar, R; Ghica, C; Ottaviano, L; Gao, JF; Politano, A

Published: JUL 15 2023, APPLIED SURFACE SCIENCE, 625, 157132, DOI: 10.1016/j.apsusc.2023.157132

Chiral materials showing Kramers-Weyl fermions represent a suitable platform for quantum technology, i.e., for engineering quantum solenoids, spin-torque devices, polarization-sensitive photodetectors based on quantized circular photogalvanic effect, etc. Accordingly, the stability of this class of materials in oxidative environments, such as the ambient atmosphere, should be carefully investigated to succeed in technology transfer. Here, taking as case-study example the well-recognized topological chiral system cadmium diarsenide (CdAs2), we assess its chemical reactivity towards ambient gases (oxygen and water) and air by density functional theory and experiments. The surface of CdAs2 evolves into an oxide skin, but its thickness remains nanometric even after one year in air, as directly imaged by high-resolution transmission electron microscopy. Accordingly, it is evident that future quantum devices based on Kramers-Weyl fermions could be stable in air, as the oxide layer formed on chiral quantum materials only represents a native oxide, which actually protects bulk features, including Kramers-Weyl fermions (correlated to bulk band structure), from degradation in air.

6. Fermiology of Chiral Cadmium Diarsenide CdAs₂, a Candidate for Hosting Kramers-Weyl Fermions

Authors: Mazzola, F; Zhang, YX; Olszowska, N; Rosmus, M; D'Olimpio, G; Istrate, MC; Politano, GG; Vobornik, I; Sankar, R; Ghica, C; Gao, JF; Politano, A

Published: MAR 23 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, DOI: 10.1021/acs.jpclett.3c00005

Nonmagnetic chiral crystals are a new class of systems hosting Kramers-Weyl Fermions, arising from the combination of structural chirality, spin- orbit coupling (SOC), and time-reversal symmetry. These materials exhibit nontrivial Fermi surfaces with SOC-induced Chern gaps over a wide energy range, leading to exotic transport and optical properties. In this study, we investigate the electronic structure and transport properties of CdAs2, a newly reported chiral material. We use synchrotron-based angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) to determine the Fermiology of the (110)-terminated CdAs2 crystal. Our results, together with complementary magnetotransport measurements, suggest that CdAs2 is a promising candidate for novel topological properties protected by the structural chirality of the system. Our work sheds light on the details of the Fermi surface and topology for this chiral quantum material, providing useful information for engineering novel spintronic and optical devices based on quantized chiral charges, negative longitudinal magnetoresistance, and nontrivial Chern numbers.

7. High-performance and self-powered visible light photodetector using multiple coupled synergetic effects

Authors: Silva, JPB; Vieira, EMF; Gwozdz, K; Silva, NE; Kaim, A; Istrate, MC; Ghica, C; Correia, JH; Pereira, M; Marques, L; MacManus-Driscoll, JL; Hoye, RLZ; Gomes, MJM

Published: 2023 NOV 22 2023, MATERIALS HORIZONS, DOI: 10.1039/d3mh01725g

In this work, we demonstrate, for the first time, that coupling together the pyroelectric effect, the photovoltaic effect and the plasmonic effect is a novel method to significantly enhance the performance of self-powered photodetectors in the visible region. Photodetectors based on tri-layered heterojunction of n-Si/p-SnO/n-ZnO through the inclusion of silver (Ag) nanoparticles (NPs) at the SnO/ZnO interface were fabricated. The photo-response of the device, with excitation from a chopped 650 nm wavelength laser, was carefully investigated, and it was shown that the photodetector performance is enhanced the most with the inclusion of spheroidal Ag NPs with similar to 70 nm diameter. The Al/Si/SnO/Ag NPs/ZnO/ITO device exhibited an optimum responsivity, detectivity and sensitivity of 210.2 mA W-1, 5.47 x 109 Jones and 15.0 x 104, respectively, together with a rise and fall time of 2.3 and 51.3 mu s, respectively, at a laser power density of 317 mW cm-2 and at a chopper frequency of 10 Hz. The present photodetectors are more than twice as responsive as the current best-performing ZnO-based pyro-phototronic photodetectors and they also exhibit other competitive features, such as detectivity, and fall and rise times. Therefore, by exploiting the plasmonic effect of the Ag NPs together with the pyroelectric effect in a ZnO film, and the photovoltaic effect at a Si/SnO junction, all in a single device, photodetectors were developed with state-of-the-art performance for the visible region. Coupling together the pyroelectric effect, the photovoltaic effect and the plasmonic effect is a novel method to significantly enhance the performance of self-powered photodetectors in the visible region.

8. Hydrogen Production Mechanism in Low-Temperature Methanol Decomposition Catalyzed by Ni3Sn4 Intermetallic Compound: A Combined Operando and Density Functional Theory Investigation

Authors: Mauri, S; D'Olimpio, G; Ghica, C; Braglia, L; Kuo, CN; Istrate, MC; Lue, CS; Ottaviano, L; Klimczuk, T; Boukhvalov, DW; Politano, A; Torelli, P

Published: FEB 9 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, DOI: 10.1021/acs.jpclett.2c03471

Hydrogen production from methanol decomposition to syngas (H2 + CO) is a promising alternative route for clean energy transition. One major challenge is related to the quest for stable, cost-effective, and selective catalysts operating below 400 degrees C. We illustrate an investigation of the surface reactivity of a Ni3Sn4 catalyst working at 250 degrees C, by combining density functional theory, operando X-ray absorption spectroscopy, and high-resolution transmission electron microscopy. We discovered that the catalytic reaction is driven by surface tin-oxide phases, which protects the underlying Ni atoms from irreversible chemical modifications, increasing the catalyst durability. Moreover, we found that Sn content plays a key role in enhancing the H2 selectivity, with respect to secondary products such as CO2. These findings open new perspectives for the engineering of scalable and low-cost catalysts for hydrogen production.

9. Cost-effective, high-performance Ni₃Sn₄ electrocatalysts for methanol oxidation reaction in acidic environments

Authors: Boukhvalov, DW; D'Olimpio, G; Liu, JZ; Ghica, C; Istrate, MC; Kuo, CN; Politano, GG; Lue, CS; Torelli, P; Zhang, LX; Politano, A

Published: MAY 16 2023, CHEMICAL COMMUNICATIONS, 59, DOI: 10.1039/d3cc01623d

Methanol (CH3OH) oxidation offers a promising avenue for transitioning to clean energy, particularly in the field of direct methanol fuel cells (DMFCs). However, the development of efficient and cost-effective catalysts for the methanol oxidation reaction (MOR) remains a critical challenge. Herein, we report the exceptional electrocatalytic activity and stability of Ni3Sn4 toward MOR in acidic media, achieving a performance comparable to that of commercial Pt/C catalysts. Our catalyst design incorporates Earth-abundant Ni and Sn elements, resulting in a material that is 1800 times more cost-effective than Pt/C. Density functional theory (DFT) modeling substantiates our experimental findings, shedding light on the favorable reaction mechanisms and kinetics on the Ni3Sn4 surface. Additionally, the as-synthesized Ni3Sn4 electrocatalyst demonstrates commendable durability, maintaining its electrocatalytic activity even after prolonged exposure to harsh acidic conditions.

10. Solution-processed In₂Se₃ nanosheets for ultrasensitive and highly selective NO₂ gas sensors

Authors: D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A

Published: JUN 13 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d3ta01390a

In this work, we demonstrate that solution-processed In2Se3 nanosheets exhibit exceptional selectivity and sensitivity to NO2 gas, making them a promising candidate for gas detection systems. Theoretical simulations and surface-science experiments reveal the unique surface properties of In2Se3 nanosheets, which prevent physisorption of oxygen, carbon monoxide, and carbon dioxide, making them remarkably stable towards oxidation and CO-poisoning. Moreover, we show that NO2 molecules adsorb stably on In2Se3 nanosheets, particularly on Se vacancies, even at high temperatures. The coadsorption of water further enhances NO2 sticking on the In2Se3 surface, making it an ideal material for gas sensing applications in humid and harsh environments. The fabricated In2Se3 gas sensors exhibit excellent and reversible sensing response to NO2 gas, with a limit of detection of 5 ppb at 300 degrees C, and a highly selective response to NO2 compared to other gases and volatile organic compounds. Our sensors outperform other two-dimensional (2D) semiconductors, metal oxides, and their heterostructures, thanks to the unique surface properties of In2Se3 nanosheets. Importantly, the number of layers and termination of the surface almost have no impact on the sensing performance of In2Se3, which is advantageous for practical applications. The high sensitivity, selectivity, and stability of In2Se3 nanosheets make them an exciting platform for the fabrication of high-performance gas sensors, particularly in harsh environments, such as industrial settings or outdoor monitoring. Moreover, our solution processing approach enables scalable production of the sensors. Additionally, their unique surface properties make them an attractive candidate for developing complex composite nanostructures with tailored gas sensing characteristics for various applications.

11. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

Authors: D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A

Published: 2023 MAY 31 2023, JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d3ta01390a

12. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

Authors: Lenzi, V; Silva, JPB; Smid, B; Matolin, V; Istrate, CM; Ghica, C; MacManus-Driscoll, JL; Marques, L

Published: 2023 MAR 6 2023, ENERGY & ENVIRONMENTAL MATERIALS, DOI: 10.1002/eem2.12500

Rhombohedral phase HfxZr1-xO2 (HZO, x from 0 to 1) films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling, as is normally the case for the more commonly studied orthorhombic phase. However, a large spontaneous polarization observed in rhombohedral films is not fully understood, and there are also large discrepancies between experimental and theoretical predictions. In this work, in rhombohedral ZrO2 thin films, we show that oxygen vacancies are not only a key factor for stabilizing the phase, but they are also a source of ferroelectric polarization in the films. This is shown experimentally through the investigation of the structural properties, chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature (400 degrees C) in an oxygen environment to reduce the V-O concentration compared. The experimental work is supported by density functional theory (DFT) calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO2 films. The DFT calculations also show that V-O contribute to the ferroelectric polarization. Our findings reveal the importance of V-O for stabilizing rhombohedral ZrO2 thin films with superior ferroelectric properties.

13. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAY 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202207390

A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx/W(14 nm)/ZrO2(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 mu C cm(-2), remnant polarization of 12.7 mu C cm(-2) and coercive field of 1.2 MV cm(-1). The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 x 10(5) cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.

14. Cost-effective, high-performance Ni3Sn4 electrocatalysts for methanol oxidation reaction in acidic environments

Authors: Boukhvalov, DW; D'Olimpio, G; Liu, JZ; Ghica, C; Istrate, MC; Kuo, CN; Politano, GG; Lue, CS; Torelli, P; Zhang, LX; Politano, A

Published: MAY 16 2023, CHEMICAL COMMUNICATIONS, 59, DOI: 10.1039/d3cc01623d

15. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

Authors: D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A

Published: JUN 13 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d3ta01390a

16. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

Authors: Mazzola, F; Zhang, YX; Olszowska, N; Rosmus, M; D'Olimpio, G; Istrate, MC; Politano, GG; Vobornik, I; Sankar, R; Ghica, C; Gao, JF; Politano, A

Published: 2023 MAR 23 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.3c00005

17. The influence of the synthesis method on Gd2O3 morpho-structural properties and sensitivity to CO2 under in-field conditions

Authors: Simion, CE; Vlaicu, ID; Iacoban, AC; Mihalcea, CG; Ghica, C; Stanoiu, A

Published: FEB 15 2023, MATERIALS CHEMISTRY AND PHYSICS, 296, 127354, DOI: 10.1016/j.matchemphys.2023.127354

In this study, we report the implications of the synthesis method on Gd2O3 sensitivity to CO2. The rare-earth oxide was prepared by wet chemical co-precipitation and by hydrothermal method. The obtained powders labelled Gd2O3-CoP and Gd2O3-HT were deposited as thick films over commercial Al2O3 substrates provided with Pt electrodes and a back-side heater. Both powders consist of the same crystallographic phase, with a significant difference appearing in selected area electron diffraction patterns, transmission electron microscopy images at higher magnification and X-ray diffraction spectra, with respect to the crystallization degree. The associated role in sensing properties is revealed via electrical resistance variations determined by CO2 concen-trations in the range between 400 and 3000 ppm and variable relative humidity between 0 and 50%RH, similar to the in-field atmosphere. The proposed CO2 interaction mechanism is based on phenomenological in-vestigations which highlight the electronic affinity variation as the effect of dipoles induced by the in-field conditions on the Gd2O3 surface.

18. Hydrogen Production Mechanism in Low-Temperature Methanol Decomposition Catalyzed by Ni3Sn4 Intermetallic Compound: A Combined Operando and Density Functional Theory Investigation

Authors: Mauri, S; D'Olimpio, G; Ghica, C; Braglia, L; Kuo, CN; Istrate, MC; Lue, CS; Ottaviano, L; Klimczuk, T; Boukhvalov, DW; Politano, A; Torelli, P

Published: FEB 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.2c03471

19. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

Authors: Lenzi, V; Silva, JPB; Smid, B; Matolin, V; Istrate, CM; Ghica, C; MacManus-Driscoll, JL; Marques, L

Published: MAR 2023, ENERGY & ENVIRONMENTAL MATERIALS, DOI: 10.1002/eem2.12500

20. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAR 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202207390

21. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

Authors: Mazzola, F; Zhang, YX; Olszowska, N; Rosmus, M; D'Olimpio, G; Istrate, MC; Politano, GG; Vobornik, I; Sankar, R; Ghica, C; Gao, JF; Politano, A

Published: MAR 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.3c00005

22. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO₂ Thin Films

Authors: Lenzi, V; Silva, JPB; Smid, B; Matolin, V; Istrate, CM; Ghica, C; MacManus-Driscoll, JL; Marques, L

Published: 2023 MAR 6 2023, ENERGY & ENVIRONMENTAL MATERIALS, DOI: 10.1002/eem2.12500

23. Ferroelectric Orthorhombic ZrO₂ Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAY 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202207390

24. 3D Porous Collagen Matrices-A Reservoir for In Vitro Simultaneous Release of Tannic Acid and Chlorhexidine

Authors: Brazdaru, L; Staicu, T; Kaya, MGA; Chelaru, C; Ghica, C; Cîrcu, V; Leca, M; Ghica, MV; Micutz, M

Published: JAN 2023, PHARMACEUTICS, 15, 76, DOI: 10.3390/pharmaceutics15010076

The treatment of wounds occurring accidentally or as a result of chronic diseases most frequently requires the use of appropriate dressings, mainly to ensure tissue regeneration/healing, at the same time as treating or preventing potential bacterial infections or superinfections. Collagen type I-based scaffolds in tandem with adequate antimicrobials can successfully fulfill these requirements. In this work, starting from the corresponding hydrogels, we prepared a series of freeze-dried atelocollagen type I-based matrices loaded with tannic acid (TA) and chlorhexidine digluconate (CHDG) as active agents with a broad spectrum of antimicrobial activity and also as crosslinkers for the collagen network. The primary aim of this study was to design an original and reliable algorithm to in vitro monitor and kinetically analyze the simultaneous release of TA and CHDG from the porous matrices into an aqueous solution of phosphate-buffered saline (PBS, pH 7.4, 37 degrees C) containing micellar carriers of a cationic surfactant (hexadecyltrimethylammonium bromide, HTAB) as a release environment that roughly mimics human extracellular fluids in living tissues. Around this central idea, a comprehensive investigation of the lyophilized matrices (morpho-structural characterization through FT-IR spectroscopy, scanning electron microscopy, swelling behavior, resistance against the collagenolytic action of collagenase type I) was carried out. The kinetic treatment of the release data displayed a preponderance of non-Fickian-Case II diffusion behavior, which led to a general anomalous transport mechanism for both TA and CHDG, irrespective of their concentrations. This is equivalent to saying that the release regime is not governed only by the gradient concentration of the releasing components inside and outside the matrix (like in ideal Fickian diffusion), but also, to a large extent, by the relaxation phenomena of the collagen network (determined, in turn, by its crosslinking degree induced by TA and CHDG) and the dynamic capacity of the HTAB micelles to solubilize the two antimicrobials. By controlling the degree of physical crosslinking of collagen with a proper content of TA and CHDG loaded in the matrix, a tunable, sustainable release profile can be obtained.

25. Improving the Efficiency of Gallium Telluride for Photocatalysis, Electrocatalysis, and Chemical Sensing through Defects Engineering and Interfacing with its Native Oxide

Authors: Bondino, F; Duman, S; Nappini, S; D'Olimpio, G; Ghica, C; Mazzola, F; Istrate, MC; Jugovac, M; Vorokhta, M; Santoro, S; Gurbulak, B; Locatelli, A; Boukhvalov, DW; Politano, A

Published: AUG 2022, ADVANCED FUNCTIONAL MATERIALS, 2205923, DOI: 10.1002/adfm.202205923

Gallium telluride (GaTe) is a van der Waals semiconductor, currently adopted for photonic and optoelectronic devices. However, the rapid degradation of GaTe in air, promoted by Te vacancies, is detrimental for device applications. Here, it is demonstrate that the surface oxidation of GaTe can be unexpectedly exploited for expanding the breadth of applications of GaTe. Specifically, the formation of a nanoscale sub-stoichiometric wide-band-gap Ga2O3 skin, promoted by Te vacancies, over narrow-band-gap GaTex upon air exposure is beneficial for electrocatalysis, photocatalysis, and gas sensing . In particular, the Heyrovsky step (H-ads + H+ + e(-) -> H-2) of hydrogen evolution reaction in an acidic medium is barrier-free for the sub-stoichiometric gallium-oxide/gallium-telluride heterostructure, which also enables a significant reduction of costs with respect to state-of-the-art Pt/C electrodes. In the photocatalytic process, the photo-generated electrons migrate from GaTe to Ga2Ox skin, which acts as the chemically active side of the interface. Moreover, the Ga2O3/GaTe heterostructure is a suitable platform for sensing of H2O, NH3, and NO2 at operational temperatures extended up to 600 degrees C (useful for gas detection in combustion processes), mainly due to the increased area of charge redistribution after adsorption achieved upon oxidation of GaTe.

26.
NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 high-entropy layered oxide - experimental and theoretical evidence of high electrochemical performance in sodium batteries

Authors: Walczak, K; Plewa, A; Ghica, C; Zajac, W; Trenczek-Zajac, A; Zajac, M; Tobo, J; Molenda, J

Published: MAY 2022, ENERGY STORAGE MATERIALS, 47, 514, DOI: 10.1016/j.ensm.2022.02.038

Li-ion batteries, widely used in portable electronics, electric vehicles, and energy storage systems, are an integral element of our daily life. However, the limitation of lithium sources, which leads to high prices, prompts the search for alternatives. Recently there has been noticed a rapid interest in Na-ion batteries technology. Especially, suitable cathode structures are investigated to accumulate larger sodium ions. In this paper, the high entropy layered oxide NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 is presented which achieves superior electrochemical properties with a stable capacity of ca. 180 mAh g(-1). The understanding of its high performance is based on a complex study of the multiphase intercalation mechanism. The combination of advanced structural analysis by XAS, in situ XRD, TEM, and computational DFT modelling gives a new concept on the nature of O3-P3 structure reorganization. The presented experimental and theoretical evidence indicates that the P3 phase of layered oxides is energetically favourable for a lower sodium content for specific transition metal-oxide pair distance. Fundamental understanding of the nature of phase transformation is crucial for tailoring structural composition, where the desirable O3-P3 reorganization will occur, resulting in achieving high-performance cathodes.

27. Chitosan-Hyaluronan Nanoparticles for Vinblastine Sulfate Delivery: Characterization and Internalization Studies on K-562 Cells

Authors: Cannava, C; De Gaetano, F; Stancanelli, R; Venuti, V; Paladini, G; Caridi, F; Ghica, C; Crupi, V; Majolino, D; Ferlazzo, G; Tommasini, S; Ventura, CA

Published: MAY 2022, PHARMACEUTICS, 14, 942, DOI: 10.3390/pharmaceutics14050942

In the present study, we developed chitosan/hyaluronan nanoparticles (CS/HY NPs) for tumor targeting with vinblastine sulfate (VBL), that can be directed to the CD44 transmembrane receptor, over-expressed in cancer cells. NPs were prepared by coating with HY-preformed chitosan/tripolyphosphate (CS/TPP) NPs, or by polyelectrolyte complexation of CS with HY. NPs with a mean hydrodynamic radius (R-H) of 110 nm, 12% polydispersity index and negative zeta potential values were obtained by a direct complexation process. Transmission Electron Microscopy (TEM) images showed spherical NPs with a non-homogeneous matrix, probably due to a random localization of CS and HY interacting chains. The intermolecular interactions occurring between CS and HY upon NPs formation were experimentally evidenced by micro-Raman (mu-Raman) spectroscopy, through the analysis of the spectral changes of characteristic vibrational bands of HY during NP formation, in order to reveal the involvement of specific chemical groups in the process. Optimized NP formulation efficiently encapsulated VBL, producing a drug sustained release for 20 h. In vitro studies demonstrated a fast internalization of labeled CS/HY NPs (within 6 h) on K-562 human myeloid leukemia cells. Pre-saturation of CD44 by free HY produced a slowing-down of NP uptake over 24 h, demonstrating the need of CD44 for the internalization of HY-based NPs.

28. Influence of relative humidity on CO2 interaction mechanism for Gd-doped SnO2 with respect to pure SnO2 and Gd2O3

Authors: Ghica, C; Mihalcea, CG; Simion, CE; Vlaicu, ID; Ghica, D; Dinu, IV; Florea, OG; Stanoiu, A

Published: OCT 1 2022, SENSORS AND ACTUATORS B-CHEMICAL, 368, 132130, DOI: 10.1016/j.snb.2022.132130

The paper aims to identify the CO2 interaction mechanism for chemical sensors based on Gd-doped SnO2, SnO2 and Gd2O3 powders deposited as thick sensitive layers. The low reactivity of CO2 conferred by the thermodynamic stability and chemical inertia can be offset by the presence of relative humidity. The sensitive powders were prepared by wet chemical co-precipitation method. The Gd concentration was varied from 1% to 20 at% in order to determine the limit for Gd integration as a doping ion prior to chemical segregation as a secondary phase. Analytical transmission electron microscopy points to a homogeneous Gd doping of the nanostructured SnO2 powders for low doping concentrations and the formation of a nanocomposite based on SnO2 as main phase and cubic Gd2O3 as secondary phase for the highly doped samples. The electrical resistance is either influenced by the density of oxygen vacancies, or is the result of compensation for two opposite behaviours into the SnO2- Gd2O3 nanocomposite structures. The CO2 exposure to humid atmosphere determines distinct behaviours cor-responding to SnO2 and Gd2O3 as constitutive elements. The associated CO2 interaction mechanism is based on simultaneous DC electrical resistance and Contact Potential Difference measurements, which allow decoupling the ionosorption from the dipolar processes, thus highlighting specific chemical interactions on the SnO2 and Gd2O3 surfaces.

29. NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 high-entropy layered oxide - experimental and theoretical evidence of high electrochemical performance in sodium batteries

Authors: Walczak, K; Plewa, A; Ghica, C; Zajac, W; Trenczek-Zajac, A; Zajac, M; Tobo, J; Molenda, J

Published: MAY 2022, ENERGY STORAGE MATERIALS, 47, DOI: 10.1016/j.ensm.2022.02.038

30. Charge State Effects in Swift-Heavy-Ion-Irradiated Nanomaterials

Authors: Luketic, KT; Hanzek, J; Mihalcea, CG; Dubcek, P; Gajovic, A; Siketic, Z; Jaksic, M; Ghica, C; Karlusic, M

Published: JUN 2022, CRYSTALS, 12, 865, DOI: 10.3390/cryst12060865

The aim of this experimental work was to investigate the influence of the ion beam charge state on damage production in nanomaterials. To achieve this, we employed Raman spectroscopy, atomic force microscopy, and transmission electron microscopy to investigate nanomaterials irradiated by a 23 MeV I beam. We found a significant influence of the ion charge state on damage production in monolayer graphene, but found no evidence of this effect in bilayer and trilayer graphene, nor in graphite. Furthermore, we found no evidence of this effect in CaF2 and SiO2 nanocrystals irradiated with the same ion beam.

31. Effects of Calcination Temperature on CO-Sensing Mechanism for NiO-Based Gas Sensors

Authors: Stanoiu, A; Ghica, C; Mihalcea, CG; Ghica, D; Somacescu, S; Florea, OG; Simion, CE

Published: MAY 2022, CHEMOSENSORS, 10, 191, DOI: 10.3390/chemosensors10050191

NiO-sensitive materials have been synthesized via the hydrothermal synthesis route and calcined in air at 400 degrees C and, alternatively, at 500 degrees C. Structural, morphological, and spectroscopic investigations were involved. As such, the XRD patterns showed a higher crystallinity degree for the NiO calcined at 500 degrees C. Such an aspect is in line with the XPS data indicating a lower surface hydroxylation relative to NiO calcined at 400 degrees C. An HRTEM microstructural investigation revealed that the two samples differ essentially at the morphological level, having different sizes of the crystalline nanoparticles, different density of the surface defects, and preferential faceting according to the main crystallographic planes. In order to identify their specific gas-sensing mechanism towards CO exposure under the in-field atmosphere, the simultaneous evaluation of the electrical resistance and contact potential difference was carried out. The results allowed the decoupling of the water physisorption from the chemisorption of the ambient oxygen species. Thus, the specific CO interaction mechanism induced by the calcination temperature of NiO has been highlighted.

32. Ferroelectric properties of ZrO2 films deposited on ITO-coated glass

Authors: Silva, JPB; Sekhar, KC; Negrea, RF; Ghica, C; Dastan, D; Gomes, MJM

Published: MAR 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2021.11.152

In this work, the ferroelectric characteristics of ZrO2 thin films grown on ITO-coated glass have been investigated. The ferroelectric nature of the ZrO2 films has been studied by polarization-electric field (P-E) hysteresis loops and found to be optimum for the films processed by rapid thermal annealing at 600 degrees C. The increase in the annealing temperature improves the ferroelectric properties through the increase of the in-plane strain that causes the formation of the ferroelectric orthorhombic phase. The formation of the orthorhombic phase was confirmed through high-resolution transmission electron microscopy. The effect of the electric field on the polarization switching kinetics of ZrO2 films has been investigated revealing that the switching kinetics follows the nucleation limited switching (NLS) model. The activation fields estimated from the peak values of the polarization currents (im) and the time (tm) at which im occurs are in good agreement with the values obtained from the switching characteristic time of the NLS model. This work paves the way towards the integration of (pseudo)binary oxide thin films on cheap substrates like glass for the next-generation of non-volatile memories.

33. All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films

Authors: Vieira, EMF; Silva, JPB; Veltruska, K; Istrate, CM; Lenzi, V; Trifiletti, V; Lorenzi, B; Matolin, V; Ghica, C; Marques, L; Fenwick, O; Goncalves, LM

Published: JUL 28 2021, ACS APPLIED MATERIALS & INTERFACES, 13, 35196, DOI: 10.1021/acsami.1c09748

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (alpha) of similar to 121 and similar to 258 mu V/K, respectively, at 298 K, resulting in power factors (PF) of 180 mu W/m K-2 (for ZnO) and 37 mu W/m K-2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (P-out) of 1.8 nW (approximate to 126 mu W/cm(2)) at a temperature difference of 160 K. The output voltage (V-out) and output current (I-ou(t)) at the maximum power output of the TEG are 124 mV and 0.0146 mu A, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films.

34. Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors-The Influence of Humidity

Authors: Simion, CE; Ghica, C; Mihalcea, CG; Ghica, D; Mercioniu, I; Somacescu, S; Florea, OG; Stanoiu, A

Published: SEP 2021, CHEMOSENSORS, 9, DOI: 10.3390/chemosensors9090244

Polycrystalline NiO thick film-based gas sensors have been exposed to different test gas atmospheres at 250 degrees C and measured via simultaneous electrical resistance and work function investigations. Accordingly, we decoupled different features manifested toward the potential changes, i.e., work function, band-bending, and electron affinity. The experimental results have shown that the presence of moisture induces an unusual behavior toward carbon monoxide (CO) detection by considering different surface adsorption sites. On this basis, we derived an appropriate detection mechanism capable of explaining the lack of moisture influence over the CO detection with NiO-sensitive materials. As such, CO might have both chemical and dipolar interactions with pre-adsorbed or lattice oxygen species, thus canceling out the effect of moisture. Additionally, morphology, structure, and surface chemistry were addressed, and the results have been linked to the sensing properties envisaging the role played by the porous quasispherical-hollow structures and surface hydration.

35. Wake-up Free Ferroelectric Rhombohedral Phase in Epitaxially Strained ZrO2 Thin Films

Authors: Silva, JPB; Negrea, RF; Istrate, MC; Dutta, S; Aramberri, H; Iniguez, J; Figueiras, FG; Ghica, C; Sekhar, KC; Kholkin, AL

Published: NOV 3 2021, ACS APPLIED MATERIALS & INTERFACES, 13, 51392, DOI: 10.1021/acsami.1c15875

Zirconia- and hafnia-based thin films have attracted tremendous attention in the past decade because of their unexpected ferroelectric behavior at the nanoscale, which enables the downscaling of ferroelectric devices. The present work reports an unprecedented ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown directly on (111)-Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal (111)-oriented ZrO2 films under epitaxial compressive strain exhibiting switchable ferroelectric polarization of about 20.2 mu C/cm(2) with a coercive field of 1.5 MV/cm. Moreover, the time-dependent polarization reversal characteristics of Nb:SrTiO3/ZrO2/Au film capacitors exhibit typical bell-shaped curve features associated with the ferroelectric domain reversal and agree well with the nucleation limited switching (NLS) model. The polarization-electric field hysteresis loops point to an activation field comparable to the coercive field. Interestingly, the studied films show ferroelectric behavior per se, without the need to apply the wake-up cycle found in the orthorhombic phase of ZrO2. Overall, the rhombohedral ferroelectric ZrO2 films present technological advantages over the previously studied zirconia- and hafnia-based thin films and may be attractive for nanoscale ferroelectric devices.

36. New Phenotype and Mineralization of Biogenic Iron Oxide in Magnetotactic Bacteria

Authors: Baaziz, W; Ghica, C; Cypriano, J; Abreu, F; Anselme, K; Ersen, O; Farina, M; Werckmann, J

Published: DEC 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11123189

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles originating from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to as magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here, we tackle the question of the organization of magnetosomes, which are always described as constituted by linear chains of nanocrystals. In addition, it is commonly accepted that the iron oxide nanocrystals are in the magnetite-based phase. We show, in the case of a wild species of coccus-type bacterium, that there is a double organization of the magnetosomes, relatively perpendicular to each other, and that the nanocrystals are in fact maghemite. These findings were obtained, respectively, by using electron tomography of whole mounts of cells directly from the environment and high-resolution transmission electron microscopy and diffraction. Structure simulations were performed with the MacTempas software. This study opens new perspectives on the diversity of phenotypes within MTBs and allows to envisage other mechanisms of nucleation and formation of biogenic iron oxide crystals.

37. Nd-doped ZnO films grown on c-cut sapphire by pulsed-electron beam deposition under oblique incidence

Authors: Nistor, M; Millon, E; Cachoncinlle, C; Ghica, C; Hebert, C; Perriere, J

Published: OCT 15 2021, APPLIED SURFACE SCIENCE, 563, DOI: 10.1016/j.apsusc.2021.150287

Nd-doped ZnO thin films were grown by pulsed-electron beam deposition (PED) on c-cut sapphire substrates under oblique angle incidence, at 10-2 mbar oxygen pressure and for a substrate temperature of 500 degrees C. The films were smooth, compact and constituted with columnar grains inclined at about 17 degrees +/- 4 degrees from the normal to the substrate surface. From X-ray diffraction and transmission electron microscopy experiments, it was found that the wurtzite phase of Nd-doped ZnO thin films is observed with the c-axis inclined around 35 degrees with respect to the normal axis of the substrate, with a three-fold azimuthal symmetry. Epitaxial relationships between Nd-doped ZnO films and sapphire substrate were determined from the asymmetric X-ray diffraction and are presented compared with those obtained for the films grown by non-oblique PED. The tilt of the ZnO c-axis has been explained by the epitaxy of the (2 2 9) ZnO plane on the (0 0 l) sapphire plane, such particular epitaxial growth having never been reported previously.

38. Structure and water uptake in BaLnCo(2)O(6-delta) (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

Authors: Wachowski, SL; Szpunar, I; Sorby, MH; Mielewczyk-Gryn, A; Balaguer, M; Ghica, C; Istrate, MC; Gazda, M; Gunnaes, AE; Serra, JM; Norby, T; Strandbakke, R

Published: OCT 15 2020, ACTA MATERIALIA, 199, 310, DOI: 10.1016/j.actamat.2020.08.018

The structure of BaLnCo(2)O(6-delta) (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N-2-O-2 gas mixture at 300 degrees C revealed that among all compositions, only BaLaCo2O6-delta and BaGdCo2O6-delta exhibit significant water uptake. Surface water adsorption studies showed that the alpha, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 degrees C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

39. Low temperature CO sensing under infield conditions with in doped Pd/SnO2

Authors: Stanoiu, A; Ghica, C; Somacescu, S; Kuncser, AC; Vlaicu, AM; Mercioniu, IF; Florea, OG; Simion, CE

Published: APR 1 2020, SENSORS AND ACTUATORS B-CHEMICAL, 308, DOI: 10.1016/j.snb.2020.127717

A one-step method assisted by hydrothermal treatment was approached to obtain nanocrystalline 1 and 10 mol. % In doped 2 mol.% Pd-SnO2 powders using a non-ionic surfactant Brij52 and Polyethylene glycol 6000 (PEG) as templates. Depending on In content, the samples were labeled as Pd1InSn and Pd10InSn. The obtained materials consist of nanosized crystallites packed into micrometric grains with a high porosity, as revealed by the morphological and structural investigations (SEM, TEM). A dependence of the grain size with respect to the In content has been revealed i.e. the sample Pd1InSn was showing an average grain size of around 10 nm, whilst for the sample Pd10InSn the average grain size was found to be around 5 nm. The XPS investigations highlighted the differences occurred in the surface chemistry in terms of surface hydroxylation as well as the chemical states of Pd. The sensing properties towards different CO concentrations have been examined under infield background conditions, at low operating temperature of 50 degrees C. The sensing mechanism model for CO was discussed in detail according to the possible interplay between oxygen and water related species based on the experimentally results acquired through simultaneous electrical resistance and work function measurements.

40. Perovskite ferroelectric thin film as an efficient interface to enhance the photovoltaic characteristics of Si/SnO(x)heterojunctions

Authors: Silva, JPB; Vieira, EMF; Silva, JMB; Gwozdz, K; Figueiras, FG; Veltruska, K; Matolin, V; Istrate, MC; Ghica, C; Sekhar, KC; Kholkin, AL; Goncalves, LM; Chahboun, A; Pereira, M

Published: JUN 14 2020, JOURNAL OF MATERIALS CHEMISTRY A, 8, 11326, DOI: 10.1039/d0ta02198a

The photovoltaic (PV) response of SnOx/Si heterojunctions (HJs) through the change of the SnO and SnO(2)ratio in the samples that allows us to obtain p- or n-type SnO(x)films is investigated in this work. The values of short-circuit photocurrent density (J(sc)), open-circuit voltage (V-OC), fill factor (FF) and power conversion efficiency (PCE) are found to be 12.6 mA cm(-2), 0.23 V, 27% and 8.3%, for the p-SnOx/n-Si HJ and 10.3 mA cm(-2), 0.20 V, 20% and 4.5% for the n-SnOx/p-Si HJ. The enhanced PV effect observed in the p-SnOx/n-Si HJs can be attributed to a small band offset between SnO(x)and Si, which lowers the diffusion length that can contribute to higher recombination rate and smaller series resistance. Furthermore, the values ofJ(sc),V-OC, FF and PCE were enhanced up to 30.9 mA cm(-2), -2.0 V, 19% and 10.9%, respectively, through the insertion of a 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BCZT) ferroelectric layer between n-Si and p-SnOx. The built-in field developed at the Si/BCZT/SiOx/SnO(x)interfaces together with the depolarizing field, provides a favorable electric potential for the separation and further transport of photo generated electron-hole (e-h) pairs. This work provides a viable approach by combining ferroelectrics with p-SnOx/n-Si HJs for building efficient ferroelectric-based solar cells.

41. Aminopropyl-silica functionalized with halogen-reactive compounds for antimicrobial applications

Authors: Zarafu, I; Al Taweel, AAJ; Limban, C; Popa, M; Marutescu, L; Chifiriuc, MC; Pircalabioru, GG; Culita, D; Ghica, C; Ionita, P

Published: FEB 1 2020, MATERIALS CHEMISTRY AND PHYSICS, 241, DOI: 10.1016/j.matchemphys.2019.122353

Aminopropyl-silica nanoparticles S0 were obtained and further functionalized with eight halogen-reactive organic compounds 1-8, leading to the S1-S8 hybrid organic-inorganic materials, with spherical morphology and having a 50-200 nm size, as showed TEM analysis. These were further characterized by IR and DLS. Biological assays were performed using five microbial strains, belonging to species frequently encountered in the aetiology of human infections (Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia toll and Candida albicans). The obtained materials exhibited promising antimicrobial properties, being active against planktonic, but particularly on biofilm-embedded cells. Among the tested hybrid nanomaterials, S6 seemed to exhibit the most promising antimicrobial profile.

42. Energy storage performance of ferroelectric ZrO(2)film capacitors: effect of HfO2:Al(2)O(3)dielectric insert layer

Authors: Silva, JPB; Silva, JMB; Sekhar, KC; Palneedi, H; Istrate, MC; Negrea, RF; Ghica, C; Chahboun, A; Pereira, M; Gomes, MJM

Published: JUL 28 2020, JOURNAL OF MATERIALS CHEMISTRY A, 8, 14177, DOI: 10.1039/d0ta04984k

The present work reports for the first time, the employment of ferroelectric ZrO(2)films as energy storage capacitors utilized in pulsed power systems. Furthermore, the effect of insertion of a low permittivity dielectric HfO2:Al2O3(HAO) layer, with a thickness ranging from 2 to 8 nm, on the tunability of ferroelectric and energy storage characteristics of ZrO(2)films is assessed. The increase in thickness of the HAO layer gave rise to distorted ferroelectric loops with decreased polarization, coercive field, and hysteresis loss of the films. These results are correlated with the depolarization field induced by the insertion of the dielectric HAO layer. An optimum combination of high energy density of 54.3 J cm(-3)and good storage efficiency of 51.3% are obtained for the ZrO(2)film capacitors with 2 nm-thick HAO insert layer. These values correspond to an increase of similar to 55% and similar to 92%, from the respective values of pure ZrO(2)film capacitors. In addition, the HAO/ZrO(2)films showed a good fatigue endurance of energy storage performance over 10(9)electric field cycles. The energy storage density obtained from HAO(2 nm)/ZrO(2)film capacitor is found to be higher than that reported for several Pb-based as well as Pb-free ferroelectric ceramic films with complex compositions. The present study demonstrates that simple binary oxides such as ZrO(2)with ferroelectric behavior could be potential candidates for developing high performance energy storage capacitors.

43. HfO2-Al2O3 Dielectric Layer for a Performing Metal-Ferroelectric-Insulator-Semiconductor Structure with a Ferroelectric 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 Thin Film

Authors: Silva, JPB; Sekhar, KC; Veltruska, K; Matolin, V; Negrea, RF; Ghica, C; Oliveira, MJS; Moreira, JA; Pereira, M; Gomes, MJM

Published: SEP 22 2020, ACS APPLIED ELECTRONIC MATERIALS, 2, 2787, DOI: 10.1021/acsaelm.0c00480

In this work, the ferroelectric and fatigue characteristics of Au/0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BCZT)/Si metal-ferroelectric-semiconductor (MFS) structures are investigated. Moreover, the effect of introducing a thin dielectric HfO2-Al2O3 (HAO) layer with different thicknesses between the BCZT layer and the Si substrate on the ferroelectric characteristics in the metal-ferroelectric-insulator-semiconductor (MFIS) configuration is evaluated. It is evidenced that the insertion of the HAO layer with a thickness of 8 nm improves the memory window of the capacitance-voltage (C-V) curves by 106% compared to the value obtained in the MFS structure and reduces the leakage currents. Furthermore, the Au/BCZT/HAO (8 nm)/Si structure shows a remarkable remnant polarization (P-r) of 7.8 mu C/cm(2), with a coercive voltage of 1.9 V. The obtained value for P-r corresponds to a six times enhancement when compared to the value obtained in the Au/BCZT/Si structure. In addition, the fatigue studies reveal that the P-r obtained in the Au/BCZT/HAO/Si structure slightly decreases (3%) with continuous cycling, up to 10(9) cycles. The present work evidences that Au/BCZT/HAO/Si structures are promising for nonvolatile memory applications.

44. HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

Authors: Ghica, C; Solis, C; Munke, J; Stark, A; Gehrmann, B; Bergner, M; Rosler, J; Gilles, R

Published: JAN 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 814, DOI: 10.1016/j.jallcom.2019.152157

VDM 780 Premium is a recently developed Ni-based superalloy designed for working at high service temperatures (above 650 degrees C) while keeping the good workability of alloy 718. VDM 780 Premium is based on the austenitic matrix (gamma phase) strengthened by intermetallic Ni3Al-like precipitates (gamma' phase, fcc L1(2) structure). Other co-precipitates may be formed in function of the applied heat treatment, such as Ni3Nb-based (delta phase, orthorhombic DOa structure) or Ni3Ti-based (eta phase, hexagonal DO24 structure) precipitates. The amount as well as the size and morphology of the different precipitates depend on the heat treatments performed on the alloy, playing an important role in improving the creep properties or the behavior during forging and recrystallization. This work contains a complex study using various techniques of analytical electron microscopy and synchrotron diffraction intended to clarify the structure of the high-temperature phase formed in the newly developed VDM 780 Premium alloy. The atomic structure of the high-temperature plate-like precipitates formed in VDM 780 Premium after two different thermal treatments has been investigated in relation with the surrounding matrix lattice, proving the stacked delta/eta structure of the precipitates. (C) 2019 Published by Elsevier B.V.

45. Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties

Authors: Cojocaru, B; Avram, D; Negrea, R; Ghica, C; Kessler, VG; Seisenbaeva, GA; Parvulescu, VI; Tiseanu, C

Published: MAY 2019, ACS OMEGA, 4, 8891, DOI: 10.1021/acsomega.9b00580

Technologically relevant tetragonal/cubic phases of HfO2 can be stabilized at room temperature by doping with trivalent rare earths using various approaches denoted generically as bulk coprecipitation. Using in situ/ex situ X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy, and in situ/ex situ site-selective, time-gated luminescence spectroscopy, we show that wet impregnation of hafnia nanoparticles with 10% Eu oxide followed by mild calcination in air at 500 degrees C produces an efficient stabilization of the cubic phase, comparable to that obtained by bulk precipitation. The physical reasons behind the apparently conflictual data concerning the actual crystallographic phase and the local symmetry around the Eu stabilizer and how these can be mediated by luminescence analysis are also discussed. Apparently, the cubic crystal structure symmetry determined by XRD results in a pseudocubic/tetragonal local structure around Eu determined by luminescence. Considering the recent findings on wet impregnated CeO2 and ZrO2, it is concluded that CeO2, ZrO2, and HfO2 represent a unique case of a family of oxides that is extremely tolerant to heavy doping by wet impregnation. In this way, the same batch of preformed nanoparticles can be doped with different lanthanide concentrations or with various lanthanides at a fixed concentration, allowing a systematic and reliable investigation of the effect of doping, lanthanide type, and lanthanide concentration on the various functionalities of these technologically relevant oxides.

46. Nanoclustered Pd decorated nanocrystalline Zn doped SnO2 for ppb NO2 detection at low temperature

Authors: Somacescu, S; Ghica, C; Simion, CE; Kuncser, AC; Vlaicu, AM; Stefan, M; Ghica, D; Florea, OG; Mercioniu, IF; Stanoiu, A

Published: SEP 1 2019, SENSORS AND ACTUATORS B-CHEMICAL, 294, 156, DOI: 10.1016/j.snb.2019.05.033

Nanoclustered Pd (2 mol%) was used to decorate Zn doped SnO2 (10 mol% Zn) in order to increase its sensing performances. Zn doped SnO2 built from nanoparticles was prepared by a hydrothermal method using a nonionic surfactant -Brij52 and Tripropylamine (TPA) as co-templates. The presence of well-dispersed Zn2+ ions in the SnO2 matrix leads to a nonstoichiometric surface. Pd was deposited by subsequent wet impregnation using hydrazine as reducing agent. The as obtained powders were deposited as thick layers onto commercial substrates, in order to obtain the sensitive structures. The coexistence of a mixture of valence states (Pd-0, Pd2+ and Pd4+) was highlighted on the surface of the as prepared layers. Several aspects have been followed regarding the Zn and Pd dispersion into the SnO2 matrix: the large scale and low scale morphology (SEM and TEM/HRTEM) in relation with the synthesis route, the obtained crystallographic phases (XRD, SAED) and the way in which the Zn2+ ions are inserted into the SnO2 structure (XRD, XPS, EPR), the spatial distribution of the added chemical elements, Zn and Pd (SEM, STEM, EDS). All these morphological and structural aspects, as well as the Pd surface chemistry, have been correlated with the sensing properties of the nanostructured materials under controlled gas atmosphere. Through this study, we could harvest the specific role of the aforementioned loadings towards selective detection of low NO2 concentrations, between 350 ppb to 5 ppm, at low operating temperature of 100 degrees C, for infield conditions.

47. Bimodal mesoporous NiO/CeO2-delta-YSZ with enhanced carbon tolerance in catalytic partial oxidation of methane-Potential IT-SOFCs anode

Authors: Somacescu, S; Cioatera, N; Osiceanu, P; Calderon-Moreno, JM; Ghica, C; Neatu, F; Florea, M

Published: FEB 2019, APPLIED CATALYSIS B-ENVIRONMENTAL, 241, 406, DOI: 10.1016/j.apcatb.2018.09.065

In the present study we report on the activity, selectivity and stability of the bimodal mesoporous NiO/CeO2-delta-YSZ anodes for IT-SOFCs applications. These materials present high concentration of C3+ ions stably retained in the lattice, which proved to be efficient for the catalytic partial oxidation of CH4 to syngas in the temperature range 600-800 degrees C. The excellent carbon tolerance was proved by a comprehensive XPS analysis, which monitored the amount of carbon before and after catalytic partial oxidation of methane (CPOM) tests. The mesoporous anodes templated by hexadecyltrimethylammonium bromide (CTAB) and tripropylamine (TPA) were obtained using a hydrothermal synthesis route. The effect of Ni and Ce incorporation on the yttria stabilized zirconia (YSZ) structure, texture, morphology and surface chemistry was discussed and correlated with catalytic and electrochemical behavior. The exhaustive characterization of the bulk and surface properties of the catalysts have been accomplished by means of complementary methods: XRD, SEM / EDX / HR TEM, TGA / TPR, XPS. The electrochemical and catalytic performance were improved when the surface contains more reduced ceria and NiO was formed as secondary phase. These features lead to a large number of vacancies and consequently a better oxygen migration, which facilitate the carbon removal.

48. Tailoring the Dopant Distribution in ZnO:Mn Nanocrystals

Authors: Ghica, D; Vlaicu, ID; Stefan, M; Maraloiu, VA; Joita, AC; Ghica, C

Published: MAY 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-43388-z

The synthesis of semiconductor nanocrystals with controlled doping is highly challenging, as often a significant part of the doping ions are found segregated at nanocrystals surface, even forming secondary phases, rather than incorporated in the core. We have investigated the dopant distribution dynamics under slight changes in the preparation procedure of nanocrystalline ZnO doped with manganese in low concentration by electron paramagnetic resonance spectroscopy, paying attention to the formation of transient secondary phases and their transformation into doped ZnO. The acidification of the starting solution in the co-precipitation synthesis from nitrate precursors lead to the decrease of the Mn2+ ions concentration in the core of the ZnO nanocrystals and their accumulation in minority phases, until similar to 79% of the Mn2+ ions were localized in a thin disordered shell of zinc hydroxynitrate (ZHN). A lower synthesis temperature resulted in polycrystalline Mn-doped ZHN. Under isochronal annealing up to 250 degrees C the bulk ZHN and the minority phases from the ZnO samples decomposed into ZnO. The Mn2+ ions distribution in the annealed nanocrystals was significantly altered, varying from a uniform volume distribution to a preferential localization in the outer layers of the nanocrystals. Our results provide a synthesis strategy for tailoring the dopant distribution in ZnO nanocrystals for applications ranging from surface based to ones involving core properties.

49. Hysteretic Characteristics of Pulsed Laser Deposited 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3/ZnO Bilayers

Authors: Silva, JPB; Wang, J; Koster, G; Rijnders, G; Negrea, RF; Ghica, C; Sekhar, KC; Moreira, JA; Gomes, MJM

Published: MAY 2 2018, ACS APPLIED MATERIALS & INTERFACES, 10, 15249, DOI: 10.1021/acsami.8b01695

In the present work, we study the hysteretic behavior in the electric-field-dependent capacitance and the current characteristics of 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT)/ZnO bilayers deposited on 0.7 wt % Nb-doped (001)-SrTiO3 (Nb:STO) substrates in a metal-ferroelectric-semiconductor (MFS) configuration. The X-ray diffraction measurements show that the BCZT and ZnO layers are highly oriented along the c-axis and have a single perovskite and wurtzite phases, respectively, whereas high-resolution transmission electron microscopy revealed very sharp Nb:STO/ BCZT/ZnO interfaces. The capacitance-electric field (C-E) characteristics of the bilayers exhibit a memory window of 47 kV/cm and a capacitance decrease of 22%, at a negative bias. The later result is explained by the formation of a depletion region in the ZnO layer. Moreover, an unusual resistive switching (RS) behavior is observed in the BCZT films, where the RS ratio can be 500 times enhanced in the BCZT/ZnO bilayers. The RS enhancement can be understood by the barrier potential profile modulation at the depletion region, in the BCZT/ZnO junction, via ferroelectric polarization switching of the BCZT layer. This work builds a bridge between the hysteretic behavior observed either in the C-E and current-electric field characteristics on a MFS structure.

50. Ferroelectric photovoltaic characteristics of pulsed laser deposited 0.5Ba (Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3/ZnO heterostructures

Authors: Silva, JPB; Sekhar, KC; Cortes-Juan, F; Negrea, RF; Kuncser, AC; Connolly, JP; Ghica, C; Moreira, JA

Published: JUN 2018, SOLAR ENERGY, 167, 23, DOI: 10.1016/j.solener.2018.03.072

In this work, we investigate the photovoltaic response of Pt/0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(0.5BZT-0.5BCT)/ITO structures through the insertion of a semiconductor ZnO layer at different positions. The values of short-circuit photocurrent density (J(sc)) of the Pt/ZnO/0.5BZT-0.5BCT/ITO, Pt/0.5BZT-0.5BCT/ZnO/ITO and Pt/ZnO/0.5BZT-0.5BCT/ZnO/ITO capacitors are around 5.31, 0.0034 and 0.052 mA/cm(2), respectively. The enhanced photovoltaic (PV) effect is observed when ZnO layer is inserted between Pt and the 0.5BZT-0.5BCT layer. The built-in field developed at the ZnO/ferroelectric interface in the same direction of the depolarizing field, provides a favorable electric potential for the efficient separation and transportation of photo generated e-h pairs. Furthermore, the polarization-dependent interfacial coupling effect enhances PV effect, which is confirmed by investigating the role of polarization flipping on switchable photo response. This work provides an efficient pathway in tuning the PV response in ferroelectric-based solar cells.

51. A Study of Extended Defects in Surface Damaged Crystals

Authors: Ferrari, C; Ghica, C; Rotunno, E

Published: FEB 2018, CRYSTALS, 8, DOI: 10.3390/cryst8020067

We have analyzed by transmission electron microscopy silicon and GaAs crystals polished with sandpapers of different grain size. The surface damage induced a crystal permanent convex curvature with a radius of the order of a few meters. The curvature is due to a compressive strain generated in the damaged zone of the sample. Contrary to what was reported in the literature, the only defects detected by transmission electron microscopy were dislocations penetrating a few microns from the surface. Assuming the surface damage as a kind of continuous indentation, a simple model able to explain the observed compressive strain is given.

52. Wet chemical synthesis of ZnO-CdS composites and their photocatalytic activity

Authors: Zgura, I; Preda, N; Socol, G; Ghica, C; Ghica, D; Enculescu, M; Negut, I; Nedelcu, L; Frunza, L; Ganea, CP; Frunza, S

Published: MAR 2018, MATERIALS RESEARCH BULLETIN, 99, 181, DOI: 10.1016/j.materresbull.2017.11.013

The present study is focused on the wet chemical synthesis and the characterization of ZnO-CdS composites. The X-ray diffraction shows that the composites contain ZnO in hexagonal wurtzite structure and CdS in cubic phase. The scanning/transmission electron microscopy images reveal flower-like structures with different sizes depending on the CdS content. The optical investigations on composites reveal that the reflectance spectra disclose two thresholds of similar to 370 nm and similar to 460 nm associated with the ZnO and CdS, respectively. The photocatalytic activity measurements evidenced that the degradation efficiency of RhB in the presence of composites is higher comparatively with pristine ZnO, depending on the catalyst morphology, which varies with CdS content and the pH value of RhB solution. The electron paramagnetic resonance revealed the presence of the paramagnetic point defects in the samples. Thus, the wet chemical approaches are suitable for a large scale production of such ZnO-CdS composites having enhanced photocatalytic activity.

53. Full Tetragonal Phase Stabilization in ZrO2 Nanoparticles Using Wet Impregnation: Interplay of Host Structure, Dopant Concentration and Sensitivity of Characterization Technique

Authors: Colbea, C; Avram, D; Cojocaru, B; Negrea, R; Ghica, C; Kessler, VG; Seisenbaeva, GA; Parvulescu, V; Tiseanu, C

Published: DEC 2018, NANOMATERIALS, 8, DOI: 10.3390/nano8120988

Here, we show that wet impregnation of ZrO2 nanoparticles with 10% and 20% Eu oxide followed by thermal anneal in air above 500 degrees C produces full stabilization of the tetragonal phase of ZrO2 without evidencing any phase separation. The bare ZrO2 nanoparticles were obtained using three synthetic methods: oil in water microemulsion, rapid hydrothermal, and citrate complexation methods. The homogeneity of the solid solutions was assessed using X-ray diffraction, Raman spectroscopy, high resolution transmission electron microscopy, and advanced luminescence spectroscopy. Our findings show that wet impregnation, which is a recognized method for obtaining surface doped oxides, can be successfully used for obtaining doped oxides in the bulk with good homogeneity at the atomic scale. The limits of characterization technique in detecting minor phases and the roles of dopant concentration and host structure in formation of phase stabilized solid solutions are also analyzed and discussed.

54. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

Authors: Mihailescu, CN; Symeou, E; Svoukis, E; Negrea, RF; Ghica, C; Teodorescu, V; Tanase, LC; Negrila, C; Giapintzakis, J

Published: APR 25 2018, ACS APPLIED MATERIALS & INTERFACES, 10, 14144, DOI: 10.1021/acsami.8b01436

Controlling the semiconductor-to-metal transition temperature in epitaxial VO2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO2 epitaxial thin films grown on TiO2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V4+-V4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO2/TiO2 multilayer structures.

55. Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

Authors: Haydous, F; Scarisoreanu, ND; Birjega, R; Ion, V; Lippert, T; Dumitrescu, N; Moldovan, A; Andrei, A; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M

Published: OCT 25 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-34010-9

We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb: SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2 theta-omega scans of the symmetric (00l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L-parallel to) is preserved on larger nanoregions/ nanodomains. For higher thickness values L-parallel to is decreasing while domains tilt angles (alpha(tilt)) is increasing. The photocurrent value obtained for the thinnest sample was as high as J(ph) = 0.72 mA/cm(2), at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film's thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.

56. Impact of thickness variation on structural, dielectric and piezoelectric properties of (Ba, Ca) (Ti, Zr)O-3 epitaxial thin films

Authors: Ion, V; Craciun, F; Scarisoreanu, ND; Moldovan, A; Andrei, A; Birjega, R; Ghica, C; Di Pietrantonio, F; Cannata, D; Benetti, M; Dinescu, M

Published: FEB 1 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-20149-y

It is shown that the dielectric and piezoelectric properties of Ba(Ti0.8Zr0.2)O-3-x(Ba0.7Ca0.3)TiO3 (x = 0.45) (BCTZ 45) epitaxial thin films have a nontrivial dependence on film thickness. BCTZ 45 epitaxial films with different thicknesses (up to 400 nm) have been deposited on SrTiO3 by pulsed laser deposition and investigated by different combined techniques: conventional and off-axis X-ray diffraction, high resolution transmission electron microscopy and dielectric and piezoforce microscopy. The changes occurring in epitaxial films when their thickness increases have been attributed to a partial relaxation of misfit strain, driving the induced tetragonal symmetry in very thin films to the original rhombohedral symmetry of the bulk material in the thickest film, which influences directly and indirectly the dielectric and piezoelectric properties.

57. Ferroelectric switching dynamics in 0.5Ba(Zr0.2Ti0.8)O-3-0.5( Ba0.7Ca0.3)TiO3 thin films

Authors: Silva, JPB; Kamakshi, K; Negrea, RF; Ghica, C; Wang, J; Koster, G; Rijnders, G; Figueiras, F; Pereira, M; Gomes, MJM

Published: AUG 20 2018, APPLIED PHYSICS LETTERS, 113, DOI: 10.1063/1.5044623

In this work, the ferroelectric characteristics of 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) thin films grown on 0.7 wt. % Nb-doped (001)-SrTiO3 (Nb:STO) single-crystal have been investigated. High-resolution transmission electron microscopy and electron energy loss spectroscopy revealed a very sharp Nb:STO/BCZT interface, while selected area electron diffraction revealed the epitaxial growth of the BCZT layer on the Nb:STO substrate. The ferroelectric nature of the BCZT films have been investigated by piezoresponse force microscopy and hysteresis loops. The effect of electric field on polarization switching kinetics has been investigated and has been analyzed by the nucleation limited switching model with a Lorentzian distribution function. The local field variation was found to decrease with the increase in the electric field, and thus, the switching process becomes faster. The peak value of the polarization current and the logarithmic characteristic switching time exhibited an exponential dependence on the inverse of electric field. This model gave an excellent agreement with the experimental polarization reversal transients throughout the whole time range. Published by AIP Publishing.

58. Lipoic acid functionalized SiO2@Ag nanoparticles. Synthesis, characterization and evaluation of biological activity

Authors: Tudose, M; Culita, DC; Musuc, AM; Somacescu, S; Ghica, C; Chifiriuc, MC; Bleotu, C

Published: OCT 1 2017, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 79, 506, DOI: 10.1016/j.msec.2017.05.083

A novel nanocomposite was obtained through the covalent immobilization of lipoic acid on the surface of silver nanoparticles-decorated silica nanoparticles (SiO2@Ag). The hybrid organic inorganic material obtained was characterized by Fourier transform infrared spectroscopy, thermal analysis, scanning and transmision electron microscopy, X-ray photoelectron spectroscopy and UV-Visible spectroscopy. Its antioxidant, cytotoxic, antimicrobial activity and influence on mammalian cells cycle were evaluated. The results of this study have shown that the functionalization of SiO2@Ag with lipoic acid resulted in a composite with increased specificity of interaction with different mammalian cell lines and antioxidant activity, but with decreased cytotoxicity and antimicrobial properties. Therefore, the SiO2@Ag functionalized with lipoic acid could be successfully used in certain concentrations to modulate the cell cycle, in order to obtain the desired anti-proliferative or stimulatory therapeutic effect. (C) 2017 Elsevier B.V. All rights reserved.

59. On the threshold for ion track formation in CaF2

Authors: Karlusic, M; Ghica, C; Negrea, RF; Siketic, Z; Jaksic, M; Schleberger, M; Fazinic, S

Published: FEB 10 2017, NEW JOURNAL OF PHYSICS, 19, DOI: 10.1088/1367-2630/aa5914

There is an ongoing debate regarding the mechanism of swift heavy ion (SHI) track formation in CaF2. The objective of this study is to shed light on this important topic using a range of complementary experimental techniques. Evidence of the threshold for ion track formation being below 3 keV nm(-1) is provided by both transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy in the channelling mode, which has direct consequences for the validity of models describing the response of CaF2 to SHI irradiation. Furthermore, information about the elemental composition within the ion tracks is obtained using scanning TEM, electron energy loss spectroscopy, and with respect to the stoichiometry of the materials surface by in situ time of flight elastic recoil detection analysis. Advances in the analyses of the experimental data presented here pave the way for a better understanding of the ion track formation.

60. Lipoic Acid Gold Nanoparticles Functionalized with Organic Compounds as Bioactive Materials

Authors: Turcu, I; Zarafu, I; Popa, M; Chifiriuc, MC; Bleotu, C; Culita, D; Ghica, C; Ionita, P

Published: FEB 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7020043

Water soluble gold nanoparticles protected by lipoic acid were obtained and further functionalized by standard coupling reaction with 1-naphtylamine, 4-aminoantipyrine, and 4 0 -aminobenzo-15-crown-5 ether. Derivatives of lipoic acid with 1-naphtylamine, 4-aminoantipyrine, and 4 0 -aminobenzo-15-crown-5 ether were also obtained and characterized. All these were tested for their antimicrobial activity, as well as for their influence on mammalian cell viability and cellular cycle. In all cases a decreased antimicrobial activity of the obtained bioactive nanoparticles was observed as compared with the organic compounds, proving that a possible inactivation of the bioactive groups could occur during functionalization. However, both the gold nanoparticles as well as the functionalized bioactive nanosystems proved to be biocompatible at concentrations lower than 50 mu g/mL, as revealed by the cellular viability and cell cycle assay, demonstrating their potential for the development of novel antimicrobial agents.

61. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates

Authors: Galca, AC; Oumezzine, M; Leca, A; Chirila, CF; Kuncser, V; Kuncser, A; Ghica, C; Pasuk, I; Oumezzine, M

Published: OCT 30 2017, APPLIED PHYSICS LETTERS, 111, DOI: 10.1063/1.4998011

We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, Delta R/R(H) approximate to 150% or Delta R/R(0) approximate to 60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (T-C). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in T-C as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded. Published by AIP Publishing.

62. Exploring porous nanosilica-TEMPO as heterogeneous aerobic oxidation catalyst: the influence of supported gold clusters

Authors: Shakir, AJ; Florea, M; Culita, DC; Ionita, G; Ghica, C; Stavarache, C; Hanganu, A; Ionita, P

Published: FEB 2016, JOURNAL OF POROUS MATERIALS, 23, 254, DOI: 10.1007/s10934-015-0076-9

TEMPO stable free radical has been supported on porous silica nanoparticles in different ways and the resulted materials have been tested as heterogeneous oxidation catalyst of three benzylic alcohols using air as final oxidant and nitrosonium tetrafluoroborate as cocatalyst. Good to excellent yields were obtained. The catalytic system consists in fact in two coupled cycles, NO/NO2 and TEMPO+/TEMPO, able to convert under mild conditions (room temperature, air, metal and halogen free condition) alcohols into aldehydes or ketones. Under these conditions, supported TEMPO on silica nanoparticles containing gold clusters lowers the efficiency of the catalyst.

63. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

Authors: Scarisoreanu, ND; Craciun, F; Birjega, R; Ion, V; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M

Published: MAY 9 2016, SCIENTIFIC REPORTS, 6, DOI: 10.1038/srep25535

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (epsilon' similar to 2500) and low dielectric loss (tan delta < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.

64. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

Authors: Oumezzine, M; Galca, AC; Pasuk, I; Chirila, CF; Leca, A; Kuncser, V; Tanase, LC; Kuncser, A; Ghica, C; Oumezzine, M

Published: 2016, DALTON TRANSACTIONS, 45, 15040, DOI: 10.1039/c6dt01914e

Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature T-C (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (Delta S-M) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg(-1), somewhat lower than that of bulk Gd (410 J kg(-1)) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating Delta S-M in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (Delta S-M)(max) around T-C is proportional to (mu H-0/T-C)(2/3) in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.

65. Fast atomic diffusion in amorphous films induced by laser pulse annealing

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Kuncser, A; Lepadatu, AM; Stavarache, I; Ciurea, ML; Scarisoreanu, ND; Andrei, A; Dinescu, M

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 158, DOI:

Fast atomic diffusion was evidenced in the surface layer of amorphous thin films of oxides and semiconductors irradiated with low fluence UV pulse laser. This process takes place in a surface layer with a thickness related to the laser radiation absorption depth in the target material and was revealed by the cross section transmission electron microscopy studies. These high values of diffusivity can be explained by supposing the glass transition transformation in the amorphous structure, triggered by the action of the laser pulse field. This effect can have application for controlling structural modifications at nanoscale of the thin films surface and also for inducing structural modification of interfaces between the film and substrate.

66. Atomic scale elemental mapping of light elements in multilayered perovskite coatings

Authors: Negrea, RF; Teodorescu, VS; Ghica, C

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 255, DOI: 10.1016/j.apsusc.2015.07.106

Spherical aberration corrected transmission electron microscopes offer unprecedented capabilities in materials structural characterization down to atomic resolution. Electron energy loss spectroscopy (EELS) - spectrum imaging (SI) and annular bright field (ABF) imaging allow to simultaneously identify both the position and nature of the atomic species in a crystalline material. These techniques, along with conventional high-resolution transmission electron microscopy are particularly useful in heterostructures interfaces like epitaxial multilayers characterization, for identifying possible atomic interdiffusion at sub-nanometric scale. This paper presents the structural and compositional microanalysis down to atomic resolution of an epitaxial BaTiO3/SrRuO3/SrTiO3 ferroelectric heterostructure using complex complementary analytical electron microscopy techniques. The atomic arrangement of both heavy and light atomic species across the interfaces in the BaTiO3/SrRuO3/SrTiO3 heterostructures is revealed. (C) 2015 Elsevier B.V. All rights reserved.

67. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Vlaicu, M; Kuncser, A; Ciurea, ML; Stavarache, I; Lepadatu, AM; Scarisoreanu, ND; Andrei, A; Ion, V; Dinescu, M

Published: APR 7 2015, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 900, DOI: 10.3762/bjnano.6.92

Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 degrees C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.

68. Crystallographic holes: new insights for a beneficial structural feature for photocatalytic applications

Authors: Vajda, K; Kasa, Z; Dombi, A; Nemeth, Z; Kovacs, G; Danciu, V; Radu, T; Ghica, C; Baia, L; Hernadi, K; Pap, Z

Published: 2015, NANOSCALE, 7, 5786, DOI: 10.1039/c4nr07157c

One of the most fundamental aspects of the heterogeneous catalysis field is the manipulation of the catalysts' activity. In photocatalysis this is carried out by maximizing the right crystal plane of a semiconductor oxide. Until now, most of the papers have achieved this by a combination of different oxides, with noble metals and sometimes with carbon nanomaterials. In this work MWCNTs (multiwalled carbon nanotubes) were applied as "crystallization promoters" in a very simple, safe, one-step hydrothermal method. By this method TiO2 nano/micro crystals with exposed {001} facets were obtained in the first step. The next episode in the crystal manipulation "saga" was the modification of the (001) crystallographic plane's structure by creating ordered/own faceted "crystallographic holes". These elements are capable of further enhancing the obtained activity of titania microcrystals to a higher extent, as shown by the UV driven photocatalytic phenol degradation experiments. The appearance of the holes was "provoked" by simple calcination and their presence and influence were demonstrated by XPS and HRTEM.

69. Analysis of bimodal thermally-induced denaturation of type I collagen extracted from calfskin

Authors: Staicu, T; Circu, V; Ionita, G; Ghica, C; Popa, VT; Micutz, M

Published: 2015, RSC ADVANCES, 5, 38406, DOI: 10.1039/c5ra02708j

The most widely occurring collagen in the extracellular matrix of the mammalian tissues - type I collagen has attracted huge interest from both theoretical and practical points of view. The results presented herein are mainly confined to a study of the thermal stability of type I collagen (CI) extracted from calfskin in acidic solutions (10(-2) M HCl). A two-step process associated with the heat-induced denaturation of CI was revealed by using ultra sensitive differential scanning calorimetry. The minor endothermic transition (peak temperatures of about 30.5-30.8 degrees C) has been assigned to the defibrillation of small supramolecular CI assemblies (occurring in solution) while the major endothermic transition (about 34.8-35.0 degrees C) has been ascribed to denaturation of CI, consisting of a complete unfolding of the native triple-helical conformation of the collagen molecule. The calorimetric data were supported by information obtained from capillary viscometry performed on the same solutions. The native state of CI (molecular integrity and triple-helical conformation) for all the systems studied in this paper was confirmed by transmission electron microscopy, ultraviolet circular dichroism and capillary viscometry. At the same time, based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis and an appropriate image processing of the corresponding electropherogram, a certain degree of intramolecular crosslinking of CI was detected, mainly between alpha 1 and alpha 2 chains of the collagen triple-helix. Such a feature seems to be caused by both the nature of the extraction procedure and the storage conditions.

70. Ni-doped (CeO2-delta)-YSZ mesoarchitectured with nanocrystalline framework: the effect of thermal treatment on structure, surface chemistry and catalytic properties in the partial oxidation of methane (CPOM)

Authors: Somacescu, S; Florea, M; Osiceanu, P; Calderon-Moreno, JM; Ghica, C; Serra, JM

Published: NOV 3 2015, JOURNAL OF NANOPARTICLE RESEARCH, 17, DOI: 10.1007/s11051-015-3206-z

Ni-doped (CeO2-delta)-YSZ (5 mol% Ni oxide, 10 mol% ceria) mesoarchitectures (MA) with nanocrystalline framework have been synthesized by an original, facile and cheap approach based on Triton X100 nonionic surfactant as template and water as solvent at a strong basic pH value. Following the hydrothermal treatment under autogenous pressure (similar to 18 bars), Ni, Ce, Y, and Zr were well ordered as MA with nanocrystalline framework, assuring thermal stability. A comprehensive investigation of structure, texture, morphology, and surface chemistry was performed by means of a variety of complementary techniques (X-Ray Diffraction, XRD; Raman Spectroscopy, RS; Brunauer-Emmett-Teller, BET; Temperature-Programmed Reduction, TPR; Transmission Electron Microscopy, TEM and DF-STEM; X-ray Photoelectron Spectroscopy, XPS; Catalytic activity and selectivity). N-2 sorption measurements highlighted that the mesoporous structure is formed at 600 degrees C and remains stable at 800 degrees C. At 900 degrees C, the MA collapses, favoring the formation of macropores. The XRD and Raman Spectroscopy of all samples showed the presence of a pure, single phase with fluorite-type structure. At 900 degrees C, an increased tetragonal distortion of the cubic lattice was observed. The surface chemistry probed by XPS exhibits a mixture of oxidation states (Ce3+ + Ce4+) with high percentage of Ce3+ valence state similar to 35 % and (Ni3+ and Ni2+) oxidation states induced by the thermal treatment. These nanoparticles assembled into MA show high stability and selectivity over time in catalytic partial oxidation of methane (CPOM). These promising performances suggest an interesting prospect for introduction as anode within IT-SOFC assemblies.

71. High Permittivity (1-x)Ba(Zr0.2Ti0.8)O-3 - x(Ba0.7Ca0.3)TiO3 (x=0.45) Epitaxial Thin Films with Nanoscale Phase Fluctuations

Authors: Scarisoreanu, ND; Craciun, F; Moldovan, A; Ion, V; Birjega, R; Ghica, C; Negrea, RF; Dinescu, M

Published: NOV 4 2015, ACS APPLIED MATERIALS & INTERFACES, 7, 23992, DOI: 10.1021/acsami.5b06745

Epitaxial (1 - x)Ba(Ti0.8Zr0.2)TiO3 - x(Ba0.7Ca0.3)TiO3, x = 0.45 (BCZT 45), thin films have been deposited on (001) SrTiO3 (STO) and (001/100) SrLaAlO4 (SLAO) substrates by pulsed laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) confirmed the epitaxial growth of the films. A high structural quality has been evidenced for the BCZT/STO films. Geometric phase analysis (GPA) associated with the HRTEM enabled us to obtain microstrain analysis and the in-plane and out-of-plane lattice parameter variation on different areas. Tetragonality ratio fluctuations at nanoscale level which are relevant for the existence of nanodomains have been evidenced on the BCZT/STO films. The in-plane dielectric constant has been measured on interdigital electrodes deposited by lift-off technique on the top of the films. High values of dielectric permittivity (>3000) combined with low dielectric loss (<0.01) are obtained for BCZT 45 film deposited on STO substrate, showing nearly constant values between 1 kHz and 10 MHz. The high dielectric permittivity of BCZT thin films was attributed to their high structural quality and to the loss of rotation stability of the polarization associated with the presence of nanodomains. This results into a divergence of fluctuations of polarization direction and a peak of dielectric susceptibility. The enhanced switching of such nanodomain configuration was probed by piezoforce microscopy, by writing and reading domains during topography scanning.

72. Polarization induced self-doping in epitaxial Pb(Zr0.20Ti0.80)O-3 thin films

Authors: Pintilie, L; Ghica, C; Teodorescu, CM; Pintilie, I; Chirila, C; Pasuk, I; Trupina, L; Hrib, L; Boni, AG; Apostol, NG; Abramiuc, LE; Negrea, R; Stefan, M; Ghica, D

Published: OCT 8 2015, SCIENTIFIC REPORTS, 5, DOI: 10.1038/srep14974

The compensation of the depolarization field in ferroelectric layers requires the presence of a suitable amount of charges able to follow any variation of the ferroelectric polarization. These can be free carriers or charged defects located in the ferroelectric material or free carriers coming from the electrodes. Here we show that a self-doping phenomenon occurs in epitaxial, tetragonal ferroelectric films of Pb(Zr0.2Ti0.8)O-3, consisting in generation of point defects (vacancies) acting as donors/acceptors. These are introducing free carriers that partly compensate the depolarization field occurring in the film. It is found that the concentration of the free carriers introduced by selfdoping increases with decreasing the thickness of the ferroelectric layer, reaching values of the order of 10(26) m(-3) for 10 nm thick films. One the other hand, microscopic investigations show that, for thicknesses higher than 50 nm, the 2O/(Ti+Zr+Pb) atomic ratio increases with the thickness of the layers. These results suggest that the ratio between the oxygen and cation vacancies varies with the thickness of the layer in such a way that the net free carrier density is sufficient to efficiently compensate the depolarization field and to preserve the outward direction of the polarization.

73. Silver Azide Nanoparticles Embedded into Silica as Energetic Nano-materials

Authors: Ghica, C; Damian, R; Culita, D; Turcu, I; Ionita, P

Published: 2015, MATERIALS SCIENCE-MEDZIAGOTYRA, 21, 332, DOI: 10.5755/j01.ms.21.3.6926

Silver azide is a primary high explosive that can be initiated by different means. In this work, silver azide nanoparticles were obtained, embedded into silica, and further derivatized with biotin. TEM, DLS, and IR measurements were used to characterize the hybrid energetic nanoparticles. The hybrid nanoparticles are made from an explosive core (silver azide) and a shell (silica), to which has been attached through an organic linker a biological target vectot (biotin). These hybrid nanoparticles can be used as models to study smart energetic nano-materials

74. Applicability of the Stoner-Wohlfarth Model for Ni-Fe Graded Thin Films

Authors: Kuncser, A; Schinteie, G; Ghica, C; Antohe, S; Kuncser, V

Published: MAR 2015, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 28, 969, DOI: 10.1007/s10948-014-2684-z

Fe-Ni graded films have been prepared by co-sputtering permalloy and Fe targets at different time-power sequences. Morpho-structural and magnetic investigations have been performed by transmission electron microscopy, Xray reflectometry, conversion electron Mossbauer spectroscopy and magneto-optic Kerr effect vector magnetometry, proving the thickness dependence of the properties. A magnetization reversal involving the displacement of Bloch-type walls is characteristic for a 115 nm thick Fe-Ni graded film whereas an in-plane coherent rotation of the spins, according to a Stoner-Wohlfarth mechanism was evidence for a 23 nm thick Fe-Ni graded film.

75. Polarization-Control of the Potential Barrier at the Electrode Interfaces in Epitaxial Ferroelectric Thin Films

Authors: Pintilie, I; Teodorescu, CM; Ghica, C; Chirila, C; Boni, AG; Hrib, L; Pasuk, I; Negrea, R; Apostol, N; Pintilie, L

Published: FEB 26 2014, ACS APPLIED MATERIALS & INTERFACES, 6, 2939, DOI: 10.1021/am405508k

Electrode interface is a key element in controlling the macroscopic electrical properties of the ferroelectric capacitors based on thin films. In the case of epitaxial ferroelectrics, the electrode interface is essential in controlling the leakage current and the polarization switching, two important elements in the read/write processes of nonvolatile memories. However, the relation between the polarization bound charges and the electronic properties of the electrode interfaces is not yet well understood. Here we show that polarization charges are controlling the height of the potential barriers at the electrode interfaces in the case of Pb(Zr,Ti)O-3 and BaTiO3 epitaxial films. The results suggest that the height is set to a value allowing rapid compensation of the depolarization field during the polarization switching, being almost independent of the metals used for electrodes. This general behavior open a new perspective in engineering interface properties and designing new devices based on epitaxial ferroelectrics.

76. Strain-induced long range ferroelectric order and linear electro-optic effect in epitaxial relaxor thin films

Authors: Scarisoreanu, ND; Craciun, F; Birjega, R; Andrei, A; Ion, V; Negrea, RF; Ghica, C; Dinescu, M

Published: AUG 21 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4893364

Relaxor ferroelectrics have neither long range ferroelectric order nor structural transformation down to the lowest temperatures, and display isotropic optical properties like quadratic electro-optic effect. However, if an anisotropy is forced through an external agent, like electric field or uniaxial strain, a ferroelectric and structural long range order can be induced in these materials. Here, we show that epitaxial strain in relaxor ferroelectric thin films can be employed to induce a linear electro-optic effect, opening the path to new strain-controlled electro-optic materials. Epitaxial thin films with Pb1-3x/2LaxZr0.2Ti0.8O3 (x = 0.22) composition grown by pulsed laser deposition on (001) SrRuO3/SrTiO3 single crystal heterostructures become tetragonal below the susceptibility peak, which occurs at a temperature 140K higher as compared to bulk. These films show piezoelectric properties and almost linear electro-optic behaviour. (C) 2014 AIP Publishing LLC.

77. Nanoscale monoclinic domains in epitaxial SrRuO3 thin films deposited by pulsed laser deposition

Authors: Ghica, C; Negrea, RF; Nistor, LC; Chirila, CF; Pintilie, L

Published: JUL 14 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4889932

In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO3 layers used as bottom electrodes in multiferroic coatings onto SrTiO3 substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO3 thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO3 orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO3 bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (-4% divided by -5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO6 octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO3 structure. (C) 2014 AIP Publishing LLC.

78. Determination of the Electronic Energy Levels of Colloidal Nanocrystals using Field-Effect Transistors and Ab-Initio Calculations

Authors: Bisri, SZ; Degoli, E; Spallanzani, N; Krishnan, G; Kooi, BJ; Ghica, C; Yarema, M; Heiss, W; Pulci, O; Ossicini, S; Loi, MA

Published: AUG 27 2014, ADVANCED MATERIALS, 26, +, DOI: 10.1002/adma.201400660

Colloidal nanocrystals electronic energy levels are determined by strong size-dependent quantum confinement. Understanding the configuration of the energy levels of nanocrystal superlattices is vital in order to use them in heterostructures with other materials. A powerful method is reported to determine the energy levels of PbS nanocrystal assemblies by combining the utilization of electric-double-layer-gated transistors and advanced ab-initio theory.

79. General equivalent circuit derived from capacitance and impedance measurements performed on epitaxial ferroelectric thin films

Authors: Pintilie, L; Hrib, L; Pasuk, I; Ghica, C; Iuga, A; Pintilie, I

Published: JUL 28 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4891255

Voltage and frequency dependent capacitance measurements were performed on epitaxial BaTiO3 and Pb(Zr0.2Ti0.8)O-3 thin films deposited on single crystal SrTiO3 substrates with (001) and (111) orientations. The measured capacitors have common bottom SrRuO3 contact and different metals as top electrodes: SrRuO3, Pt, Cu, Al, and Au. The capacitance-voltage characteristics were used to extract information regarding the density of the free carriers and the linear contribution to the static dielectric constant. The frequency dependent impedance was used to develop a suitable equivalent circuit for the epitaxial ferroelectric capacitors. It was found that the frequency dependence of the imaginary part of the impedance can be well simulated, in all cases, using a circuit composed of Schottky-type capacitance related to electrode interfaces, contact resistance, and the R-C parallel connection related to the ferroelectric volume of the film. Values for the components of the equivalent circuit were obtained by fitting the experimental data with the simulated curves. These were then used to extract quantities such as dielectric constant in the ferroelectric volume, the width of the depletion layers, and the apparent built-in potential. It was found that, although the investigated capacitors are of different ferroelectric materials, grown on substrates with different orientations, and having different metals as top electrodes, the values for the capacitance associated with the Schottky contacts and the apparent built-in potential are not very different. The results suggest a strong influence of ferroelectric polarization on the electrode interface properties in the case of epitaxial ferroelectric films. (C) 2014 AIP Publishing LLC.

80. Synthesis and exceptional thermal stability of Mg-based bimetallic nanoparticles during hydrogenation

Authors: Krishnan, G; Negrea, RF; Ghica, C; ten Brink, GH; Kooi, BJ; Palasantzas, G

Published: 2014, NANOSCALE, 6, 11970, DOI: 10.1039/c4nr03885a

Here we report the extraordinary thermal stability of Mg rich bimetallic nanoparticles (NPs), which is important for hydrogen storage technology. The enhanced NP stability is accomplished because of two critical improvements: (i) no void development within NPs (nanoscale Kirkendall effect) during their formation and (ii) suppressed Mg evaporation and NP hollowing during Mg hydrogenation at elevated temperature. The mechanism leading to the improved thermal stability of Mg-based bimetallic NPs is shown to be due to MgH2 hydride formation before evaporation can take place. These findings were tested for various compositions of Mg with Ni, Cu, and Ti, which are interesting combinations of materials for hydrogen storage systems. To achieve this we first demonstrate the synthesis mechanism of Mg-Ni and Mg-Cu NPs, which is well controlled at the single particle level, in order to accomplish multi-shell, alloy and intermetallic structures of interest for hydrogen storage tests. Aberration corrected transmission electron microscopy was carried out to unravel the detailed atomic structure and composition of the bimetallic NPs after production, processing, and hydrogenation. Finally, a simple and effective methodology is proposed for tuning the composition of the Mg-based bimetallic NPs based on the temperature-dependent nucleation behavior of NPs in the gas-phase.

81. Nanomechanical characterization of bioglass films synthesized by magnetron sputtering

Authors: Popa, AC; Marques, VMF; Stan, GE; Husanu, MA; Galca, AC; Ghica, C; Tulyaganov, DU; Lemos, AF; Ferreira, JMF

Published: FEB 28 2014, THIN SOLID FILMS, 553, 172, DOI: 10.1016/j.tsf.2013.10.104

Bioactive glasses are osteoproductive-type inorganic materials possessing the highest indices of bioactivity in both bulk and thin film forms. The prerequisites for reliable implant-type coatings are both their biological and mechanical performances. Whilst the bioglass films' structural, chemical and biological properties have been studied extensively, information about their mechanical performance is scarce. Here, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and pull-out measurements were employed to assess the morphological, chemical, structural and mechanical properties of the bioglass films deposited onto Ti substrates by radio-frequency magnetron sputtering (RF-MS). The biological safety of the thin bioglass films was evaluated preliminarily in vitro by investigating the adherence, proliferation and cytotoxicity of fibroblast cells cultivated on their surface. Our study emphasize the versatility of RF-MS, showing how bioglass films' features such as composition, structure, bonding strength, hardness, elastic modulus and biological response can be conveniently adapted by tuning the RF-MS working conditions, and therefore demonstrating the unexplored potential of this deposition technique for preparing quality biomimetic glass coatings. (C) 2013 Elsevier B. V. All rights reserved.

82. Evaluation of the Segregation of Paramagnetic Impurities at Grain Boundaries in Nanostructured ZnO Films

Authors: Ghica, D; Stefan, M; Ghica, C; Stan, GE

Published: AUG 27 2014, ACS APPLIED MATERIALS & INTERFACES, 6, 14238, DOI: 10.1021/am5035329

Magnetic and electrical properties of the nanostructured ZnO films are affected by the nonrandom distribution of impurities in the film due to segregation at grain boundaries (GBs) or extended defects. However, mapping the nature and distribution of the impurities in the film is not trivial. Here we demonstrate a simple, statistically relevant, and nondestructive procedure of quantitative determination of the paramagnetic impurities segregated at the GBs in nanostructured semiconducting and insulating films. From correlated electron paramagnetic resonance and transmission electron microscopy investigations, we determined the localization of trace amounts of Mn2+ ions, present as native impurities in a ZnO film deposited by magnetron sputtering at room temperature. In the as-deposited ZnO film, the Mn2+ ions were all localized in nanosized pockets of highly disordered ZnO dispersed between nanocrystalline columns. After the samples had been annealed in air at >400 degrees C, the size of the intercrystalline region decreased and the diffusion in GBs was activated, resulting in the localization of a portion of the Mn2+ ions in the peripheral atomic layers of the ZnO columns neighboring the GBs. The proportion of Mn2+ ions still localized at the GBs after annealing at 600 degrees C was 37%. The proposed method for the assessment of the presence and nature of impurities and the quantitative evaluation of their distribution in semiconducting and insulating nanostructures is expected to find direct applications in nanotechnology, in the synthesis and quality assurance of thin films for spintronics and opto- and nanoelectronics.

83. Focusing geometry-induced size tailoring of silver nanoparticles obtained by laser ablation in water

Authors: Stasic, J; Joksic, G; Zivkovic, L; Mihailescu, IN; Ghica, C; Kuncser, A; Trtica, M

Published: OCT 2014, LASER PHYSICS, 24, DOI: 10.1088/1054-660X/24/10/106005

Silver nanoparticles were obtained by picosecond laser ablation in water at 1064 nm, using focusing geometry to design the particles' size. The position of the target surface with respect to the focal point strongly influences the NPs' size: above and in the focus it is up to 20 nm and below focus <= 150 nm. Generated particles have a spherical shape. The solutions were further employed on human cells and the tests showed a deteriorating effect on DNA.

84. Oxide Thin Films and Nano-heterostructures for Microelectronics (MOS Structures, Ferroelectric Materials and Multiferroic Heterostructures)

Authors: Pintilie, I; Pintilie, L; Filip, LD; Nistor, LC; Ghica, C

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 108, DOI: 10.1007/978-3-662-44479-5_4

Oxide materials are becoming of increasing interest due to their large variety of physical properties such as dielectric, magnetism, superconductivity, conductivity, ferroelectricity, multiferroism, etc. In addition, interfacing oxides with other materials is conferring new or better device functionalities. The main physical properties of oxides interfaces and their impact on the electrical properties of interest for microelectronic applications are presented. Further on, this subchapter is also devoted to the investigation and understanding of interface effects observed in heterostructures containing linear (SiO2) and non-linear (ferroelectrics) dielectrics in combination with wide-band gap semiconductor materials (e.g. ZnO and SiC) with special emphasis on size effects, interface quality and the opportunity to control the emergent phenomena in Metal-Oxide-Semiconductor (MOS) and Metal-Ferroelectric-Semiconductor (MFS) materials systems.

85. Charge transfer and band bending at Au/Pb(Zr0.2Ti0.8)O-3 interfaces investigated by photoelectron spectroscopy

Authors: Apostol, NG; Stoflea, LE; Lungu, GA; Chirila, C; Trupina, L; Negrea, RF; Ghica, C; Pintilie, L; Teodorescu, CM

Published: MAY 15 2013, APPLIED SURFACE SCIENCE, 273, DOI: 10.1016/j.apsusc.2013.02.056

The growth of gold layers on Pb(Zr,Ti)O-3 (PZT) deposited on SrTiO3 is investigated by X-ray photoelectron spectroscopy in the Au thickness range 2-100 angstrom. Two phases are identified, with compositions close to nominal PZT. The 'standard' phase is represented by all binding energies (Pb 4f, Ti 2p, Zr 3d, O 1s) sensibly equal to the nominal values for PZT, whereas the 'charged' phase exhibits all core levels are shifted by similar to 1 eV toward higher binding energies. By taking into account also scanning probe microscopy images together with recent photoemission results, the 'charged' phase belongs to P(+) regions of PZT, whereas the 'normal' phase corresponds to regions with no net ferroelectric polarization perpendicular to the surface. Au deposition proceeds in a band bending of Phi(PZT) - Phi(Au) similar to 0.4-0.5 eV for both phases, identified as similar shifts toward higher binding energies of all Pb, Ti, Zr, O core levels with Au deposition. The Au 4f core level exhibits also an unusually low binding energy component 1 eV below the 'nominal' Au 4f binding energy position (metal Au). This implies the existence of negatively charged gold, or electron transfer from PZT to Au, although the 'normal' PZT phase have a higher work function, as it is derived from the band bending. Most probably this charge transfer occurs toward Au nanoparticles, which have even higher ionization energies. High resolution transmission electron microscopy evidenced the formation of such isolated nanoparticles. (C) 2013 Elsevier B.V. All rights reserved.

86. Magnetic configurations of Ni-Cu alloy nanowires obtained by the template method

Authors: Matei, E; Enculescu, I; Toimil-Molares, ME; Leca, A; Ghica, C; Kuncser, V

Published: AUG 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1863-3

High aspect ratio nanowires of Ni-Cu alloys have been synthesized by potentiostatic electrochemical deposition in etched ion-track membranes. The nickel-to-copper ratio in the nanowires was controlled via the deposition potential and electrochemical bath composition. We present a detailed study of nanowire properties including morphology, composition, and magnetic behavior. We report the magnetic configurations measured as function of the nanowire composition and discuss domain formation, anisotropy aspects, and local easy axis distributions.

87. Microstructure-related magnetic properties in Co-implanted ZnO thin films

Authors: Nistor, LC; Ghica, C; Kuncser, V; Pantelica, D; Grob, JJ; Epurescu, G; Dinescu, M

Published: FEB 13 2013, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 46, DOI: 10.1088/0022-3727/46/6/065003

Highly textured ZnO thin films were implanted with Co ions at fluences of 1 x 10(16) and 1 x 10(17) ions cm(-2). Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of similar to 2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature.

88. Functionalized magnetite silica thin films fabricated by MAPLE with antibiofilm properties

Authors: Mihaiescu, DE; Cristescu, R; Dorcioman, G; Popescu, CE; Nita, C; Socol, G; Mihailescu, IN; Grumezescu, AM; Gudovan, D; Enculescu, M; Negrea, RF; Ghica, C; Chifiriuc, C; Bleotu, C; Chrisey, DB

Published: MAR 2013, BIOFABRICATION, 5, DOI: 10.1088/1758-5082/5/1/015007

We report on the fabrication of magnetite/salicylic acid/silica shell/antibiotics (Fe3O4/SA/SiO2/ATB) thin films by matrix-assisted pulsed laser evaporation (MAPLE) to inert substrates. Fe3O4-based powder have been synthesized and investigated by XRD and TEM. All thin films were studied by FTIR, SEM and in vitro biological assays using Staphylococcus aureus and Pseudomonas aeruginosa reference strains, as well as eukaryotic HEp-2 cells. The influence of the obtained nanosystems on the microbial biofilm development as well as their biocompatibility has been assessed. For optimum deposition conditions, we obtained uniform adherent films with the composition identical with the raw materials. Fe3O4/SA/SiO2/ATB thin films had an inhibitory activity on the ability of microbial strains to initiate and develop mature biofilms, in a strain-and antibiotic-dependent manner. These magnetite silica thin films are promising candidates for the development of novel materials designed for the inhibition of medical biofilms formed by different pathogenic agents on common substrates, frequently implicated in the etiology of chronic and hard to treat infections.

89. Reversible aggregation between nanoparticles induced by acid-base interactions

Authors: Ionita, G; Ghica, C; Turcu, I; Ionita, P

Published: SEP 12 2012, CHEMICAL PHYSICS LETTERS, 546, 135, DOI: 10.1016/j.cplett.2012.08.009

Acid-base interactions between amino-silica and carboxyl-gold protected nanoparticles, functionalized or not with free stable radicals or fluorescent moieties, were studied by ESR, fluorescence, and TEM. While those nanoparticles are stable in solution, mixing them induces aggregation, due to acid-base interactions; addition of a base or an acid redissolves them. By ESR, strong spin-spin interactions were noticed; by fluorescence, only small differences may be observed, while by TEM, it was noticed that gold nanoparticles are distributed evenly on the surface of the silica nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.

90. Structure and Magnetic Properties of Nanosized Magnetite Obtained by Glass Recrystallization

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, I; Ghica, C; Sandu, E

Published: JUN 2012, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12, 5050, DOI: 10.1166/jnn.2012.4943

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mossbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.

91. Eu3+-doped CaF2 nanocrystals in sol-gel derived glass-ceramics

Authors: Secu, M; Secu, CE; Ghica, C

Published: FEB 2011, OPTICAL MATERIALS, 33, 617, DOI: 10.1016/j.optmat.2010.11.016

Glass-ceramics containing Eu3+-doped CaF2 nanocrystals of about 16 nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2-SiO2 xerogels. In the glass-ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass-ceramics and as a result an additional broad thermoluminescence peak at about 380 degrees C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals. (C) 2010 Elsevier B.V. All rights reserved.

92. Characterization of martensitic transformation in some Ni-Fe-Co-Ga ferromagnetic shape memory alloys

Authors: Tolea, F; Sofronie, M; Ghica, C; Valeanu, M

Published: MAY 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 566, DOI:

The martensitic transformation characteristics in two series of cobalt substituted Ni-Fe-Ga Ferromagnetic Shape Memory alloys have been studied by differential scanning calorimetry, X-ray diffraction, electrical resistivity and thermomagnetic measurements. Co substitution for Fe or Ni promotes an increase of the Curie temperatures but the changes of the martensitic transformation temperatures are in agreement with the valence electron concentration and unit cell volume variations. A large hysteresis observed between cooling and heating curves as feature of a first order phase transition was evidenced by r(T) and thermomagnetic measurements.

93. Modification of AlN thin films morphology and structure by temporally shaping of fs laser pulses used for deposition

Authors: Ristoscu, C; Ghica, C; Papadopoulou, EL; Socol, G; Gray, D; Mironov, B; Mihailescu, IN; Fotakis, C

Published: JUL 29 2011, THIN SOLID FILMS, 519, 6387, DOI: 10.1016/j.tsf.2011.04.065

We studied the effect of temporally pulse shaping upon the properties of thin layers synthesized by pulsed laser deposition with fs laser pulses generated by a Ti-sapphire laser source. We showed that the film morphology and structure can be gradually modified when applying mono-pulses of different duration or passing to a sequence of two pulses of different intensities. (C) 2011 Elsevier B.V. All rights reserved.

94. Introduction of the Ge nanostructures in a Si matrix via nanosphere lithography deposition

Authors: Ulmeanu, M; Ghica, C

Published: MAR 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 280, DOI:

Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of Ge with polystyrene spheres as a mask. The size distribution of the patterned Ge nanostructures is narrow with the full width at half maximum being less than 10% of the dot size. The two-dimensional patterned Ge nanostructures were further introduced in a Si matrix. Cross-section transmission electron microscopy reveals periodic dark stripes representing the deposited Ge dots in an a-Si matrix.

95. Solid-state synthesis and spark plasma sintering of SrZrO3 ceramics

Authors: Popescu, B; Enache, S; Ghica, C; Valeanu, M

Published: JUN 2 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 6399, DOI: 10.1016/j.jallcom.2011.03.009

SrZrO3 powders are obtained by solid state reaction from SrCO3 and ZrO2 precursors, without involving intermediate calcination and grinding steps. The resulted powders are essentially within a single phase, with sub-micron average crystallite size. Pellets of these powders show a relatively poor sintering behavior, when fired up to 1600 degrees C. Alternatively, spark plasma sintering technique is used in order to obtain nearly 100% dense samples at the expense of excessive grain coarsening (i.e., up to 5 mu m in diameter). Crystalline structure, composition and morphology of the specimens obtained in this work are investigated by X-ray diffraction, scanning and transmission electron microscopy together with energy dispersive X-ray spectroscopy. (C) 2011 Elsevier B.V. All rights reserved.

96. Annealing of hydrogen-induced defects in RF-plasma-treated Si wafers: ex situ and in situ transmission electron microscopy studies

Authors: Ghica, C; Nistor, LC; Vizireanu, S; Dinescu, G

Published: JUL 27 2011, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 44, DOI: 10.1088/0022-3727/44/29/295401

The smart-cut (TM) process is based on inducing and processing structural defects below the free surface of semiconductor wafers. The necessary defects are currently induced by implantation of light elements such as hydrogen or helium. An alternative softer way to induce shallow subsurface defects is by RF-plasma hydrogenation. To facilitate the smart-cut process, the wafers containing the induced defects need to be subjected to an appropriate thermal treatment. In our experiments, (0 0 1) Si wafers are submitted to 200 and 50 W hydrogen RF-plasma and are subsequently annealed. The samples are studied by transmission electron microscopy (TEM), before and after annealing. The plasma-introduced defects are {1 1 1} and {1 0 0} planar-like defects and nanocavities, all of them involving hydrogen. Many nanocavities are aligned into strings almost parallel to the wafer surface. The annealing is performed either by furnace thermal treatment at 550 degrees C, or by in situ heating in the electron microscope at 450, 650 and 800 degrees C during the TEM observations. The TEM microstructural studies indicate a partial healing of the planar defects and a size increase of the nanometric cavities by a coalescence process of the small neighbouring nanocavities. By annealing, the lined up nanometric voids forming chains in the as-hydrogenated sample coalesced into well-defined cracks, mostly parallel to the wafer surface.

97. Chemically Modified (Nano)Silica as Sensitive Material for Arginine and Lysine

Authors: Tudose, M; Culita, D; Marinescu, G; Ghica, C; Ionita, P

Published: SEP 2011, JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS, 21, 497, DOI: 10.1007/s10904-011-9470-1

Silica has been derivatized with aminopropyl groups which subsequently have been chemically modified with N-methoxy-2,6-dinitroaniline derivatives to yield a solid which changes its color in the presence of arginine or lysine, from yellow to blue. Other amino-acids (such as glycine, valine, cysteine, cystine, alanine, phenylalanine, histidine) do not showed this behavior. The same procedure may be applied to silica nanoparticles. The new materials were characterized by UV-Vis, IR, and TEM.

98. Rare-earth doped sol-gel derived oxyfluoride glass-ceramics: Structural and optical characterization

Authors: Secu, CE; Secu, M; Ghica, C; Mihut, L

Published: SEP 2011, OPTICAL MATERIALS, 33, 1774, DOI: 10.1016/j.optmat.2011.06.004

Glass-ceramics containing RE3+-doped BaF2 nanocrystals (RE = Eu, Sm, Dy, Ho and Pr) with the size below 10 nm size have been made by using the controlled crystallization at higher temperatures of the RE3+-doped SiO2-BaF2 xerogels. Photoluminescence measurements have indicated the incorporation of the RE3+ ions in both silica network and in the BaF2 nanocrystals. Thermoluminescence measurements have shown a peak whose position depends on the nature of RE3+-dopant as it follows: 140 degrees C (for Ho3+, Dy3+), 340 degrees C (for Sm3+) and 370 degrees C (for Eu3+); in Eu3+-doped SiO2 glass the TL peak is shifted to 383 degrees C. The peaks in glass-ceramics were assigned to the recombination of the electrons thermal released from the RE3+-electron traps located in both glass-matrix and BaF2 nanocrystals. Within the series the trivalent lanthanide ions act as increasingly deeper electron trapping centres. (C) 2011 Elsevier B.V. All rights reserved.

99. Growth and structural characterization of Y0.6Lu0.4Ca4O(BO3)(3) new nonlinear crystal

Authors: Gheorghe, L; Achim, A; Voicu, F; Ghica, C

Published: AUG 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1683, DOI:

The nonlinear optical (NLO) crystal Y0.6Lu0.4Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been measured to be a = 0.80711(2)nm, b = 1.60132(1)nm, c = 0.35230(8)nm and beta = 101.166(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

100. Doped aluminium based spinels synthesized by a soft chemistry method

Authors: Mindru, I; Marinescu, G; Gingasu, D; Patron, L; Diamandescu, L; Ghica, C; Mironov, B

Published: JUN 15 2010, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 170, 106, DOI: 10.1016/j.mseb.2010.02.036

Structural and optical properties of (Co0.01Zn0.99)Al2O4 and Zn(Al(1.99)Ln(0.01))O-4 (where Ln(III)=Eu(III), Tb(III)) spinels obtained by a variant of the complexation method-tartarate route were studied. The tartarate precursors have been characterized by IR, UV-vis and luminescence spectroscopy. The doped aluminium based spinets have been investigated by X-ray diffraction (XRD), transsmision electron microscopy (TEM), infrared spectroscopy (IR), ultraviolet visible spectroscopy (UV-vis) and luminescence spectroscopy. Pure spinel nanometer powders were obtained. Under excitation at 380 nm the nanoparticles exhibits strong luminescence corresponding to D-5(0) -> F-7(2) transition of Eu3+ ions and respectively, to D-5(4) -> 7 F-j (j = 3, 4, 5, 6) transition of Tb3+ ions. No blue emission from the D-5(3) state were observed. (C) 2010 Elsevier B.V. All rights reserved.

101. Specificity of defects induced in silicon by RF-plasma hydrogenation

Authors: Ghica, C; Nistor, LC; Stefan, M; Ghica, D; Mironov, B; Vizireanu, S; Moldovan, A; Dinescu, M

Published: MAR 2010, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 98, 785, DOI: 10.1007/s00339-009-5527-1

Silicon wafers have been submitted to hydrogen RF-plasma treatment in various experimental conditions. Hydrogen RF-plasma treatment induced two kinds of effects on Si wafers, depending on the treatment conditions: surface corrugation and formation of structural defects below the free surface. Atomic force microscopy (AFM) investigations showed that the surface roughness significantly increased with the treatment duration, leading to the formation of pyramidal humps on the surface. The structural defects resulting after the plasma treatments were investigated by conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) techniques. The specificity of the induced extended defects due to hydrogen decoration was emphasized. Three types of extended defects were identified and characterized: planar defects in the {111} and {100} planes and nanometric voids. Point defects related to the hydrogenation process were investigated by electron paramagnetic resonance (EPR) in correlation with the electron microscopy results.

102. ADSORPTION COMPLEXES OF COLLAGENOUS POLYPEPTIDE-IONIC SURFACTANT IN AQUEOUS MEDIUM 2. THE INFLUENCE OF ADSORPTION COMPLEXES OF POLYPEPTIDE-IONIC SURFACTANT ON THERMAL STABILITY OF COLLAGEN TYPE I

Authors: Micutz, M; Staicu, T; Sulea, D; Leca, M; Ghica, C

Published: AUG 2010, REVUE ROUMAINE DE CHIMIE, 55, 510, DOI:

In the first part of this study it has shown that the interaction between collagenous polypeptides (collagen type I with native structure of triple helix and collagen hydrolyzates with no significant secondary structure) and ionic surfactants (sodium dodecyl sulfate and hexadecyl trimethylammonium bromide) involves the formation of micelle-like clusters of ionic surfactant adsorbed onto polypeptide backbone (polypeptide-surfactant complexes) at surfactant concentrations much lower than its cmc. The present investigation is focused on the influence of polypeptide-ionic surfactant complexation on thermal denaturation of the collagen type I extracted from calfskin and young horse tendons. On the basis of capillary viscometry, a good correlation between denaturation temperatures and activation energies of viscous flow for the dilute aqueous collagen-ionic surfactant solutions at pH 2.5 and 8.0 has been found. Beginning from that, it has established that the presence of ionic surfactant reduces thermal stability of the two collagens, with a more pronounced effect in the case of sodium dodecyl sulfate. Accordingly, it has been proposed a thermal denaturation mechanism of the collagen triple helix in the presence of ionic surfactants.

103. Blue CoAl2O4 spinel via complexation method

Authors: Mindru, I; Marinescu, G; Gingasu, D; Patron, L; Ghica, C; Giurginca, M

Published: AUG 1 2010, MATERIALS CHEMISTRY AND PHYSICS, 122, 497, DOI: 10.1016/j.matchemphys.2010.03.032

Cobalt-aluminate spinel, CoAl2O4, has been synthesized by two synthesis variants of the complexation method: tartarate and gluconate routes. The complex precursors have been characterized by IR, UV-vis spectroscopy and thermal analysis. The cobalt-aluminate spinet has been investigated by XRD, IR, UV-vis and luminescence spectroscopy and TEM. The results indicated that in both cases the single-phase nanocrystalline CoAl2O4 spinet was formed. The average crystallite size from TEM images was in the range 50-60 nm. The emission spectra of CoAl2O4 in the visible region confirmed the presence of tetrahedral coordinated Co2+ ion. (C) 2010 Elsevier B.V. All rights reserved.

104. HYDROGEN-PLASMA INDUCED PLATELETS AND VOIDS IN SILICON WAFERS

Authors: Ghica, C; Nistor, LC; Mironov, B; Vizireanu, S

Published: 2010, ROMANIAN REPORTS IN PHYSICS, 62, 340, DOI:

Silicon wafers have been submitted to hydrogen RF-plasma treatment in various experimental conditions The hydrogen RF-plasma treatment on Si wafers induces two kinds of effects surface corrugation and formation of structural defects below the wafer surface The structural defects resulted after the plasma treatments have been investigated by conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) techniques The specificity of the induced extended defects due to hydrogen decoration has been emphasized

105. Organic Photovoltaic Cells Based on ZnO Thin Film Electrodes

Authors: Ghica, C; Ion, L; Epurescu, G; Nistor, L; Antohe, S; Dinescu, M

Published: FEB 2010, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 10, 1326, DOI: 10.1166/jnn.2010.1836

Due to its wide band-gap (ca. 3.4 eV), ZnO is a possible candidate material to be used as transparent electrode for a new class of photovoltaic (PV) cells. Also, an increased interest for the photovoltaic properties of several organic monomers and polymers (merocyanines, phthalocyanines and porphyrins) was noticed, because of their high optical absorption in the visible region of the spectrum allowing them to be used as potential inexpensive materials for solar cells. Preparation and properties of CuPc (copper phthalocyanine) based photovoltaic cells using ZnO thin films as transparent conductor electrodes are presented in this paper. ZnO layers are grown by pulsed laser deposition, while the organic layers are obtained by thermal evaporation. Structural characterization is performed by electron microscopy. Optical and transport properties of the mutilayered structures are obtained by electrical and spectro-photometric measurements. The influence of the ZnO-polymer interface on the external quantum efficiency (EQE) of the photovoltaic cell is clearly evidenced by our measurements.

106. Skin Layer Defects in Si by Optimized Treatment in Hydrogen RF Plasma

Authors: Ghica, C; Nistor, LC; Vizireanu, S; Dinescu, G; Moldovan, A; Dinescu, M

Published: DEC 20 2010, PLASMA PROCESSES AND POLYMERS, 7, 991, DOI: 10.1002/ppap.201000066

The first step of the smartcut (TM) process consists in inducing structural defects below the free surface of a silicon wafer, usually by implantation of light elements, such as hydrogen or helium. An alternative way to induce subsurface defects is by plasma treatment. In this work, we present a morphological and structural study on silicon wafers submitted to hydrogen plasma treatment, using two plasma-processing geometries. The parameters of the plasma treatment have been varied in order to limit the surface roughness and to confine the induced defects in a narrow region (50 nm) below the wafer surface. The morphological and structural investigations have been performed by AFM and TEM.

107. ADSORPTION COMPLEXES OF COLLAGENOUS POLYPEPTIDE-IONIC SURFACTANT IN AQUEOUS MEDIUM 1. THE FORMATION OF MICELLAR STRUCTURE OF IONIC SURFACTANT ADSORBED ONTO COLLAGENOUS POLYPEPTIDE CHAIN

Authors: Micutz, M; Staicu, T; Leca, M; Ghica, C

Published: NOV-DEC 2009, REVUE ROUMAINE DE CHIMIE, 54, +, DOI:

The paper reports on the main findings issued from studying the formation of adsorbed micelle-like clusters of ionic surfactant (sodium dodecyl sulfate and hexadecyl trimethylammonium bromide) onto molecule of collagenous polypeptide (collagen hydrolyzates and calfskin collagen type 1). Capillary viscometry, UV-circular dichroism, transmission electron microscopy and surfactant titration method were used to characterize the macromolecular component of the studied systems. To highlight the critical aggregation concentration (cac) and the critical saturation concentration (T-2) in the investigated polypeptide-surfactant systems, the steady-state fluorescence of pyrene (1(1)/1(3) rule) and the surface tension measurements (the droplet volume method) were availed. The study revealed a significant decrease of the effective micelle concentration of surfactant (cue) in the presence of polypeptide irrespective of pH and a critical concentration T-2 depending on the system composition and pH.

108. Ultrafine particles of ZnGa2O4 obtained by solution combustion and complexation methods

Authors: Gingasu, D; Mindru, I; Marinescu, G; Patron, L; Ghica, C

Published: JUL 29 2009, JOURNAL OF ALLOYS AND COMPOUNDS, 481, 895, DOI: 10.1016/j.jallcom.2009.03.193

Two soft chemistry routes - complexation and solution combustion - are explored to obtain the zinc gallate spinel ZnGa2O4. Three types of complexes, namely: (NH4)(2)[ZnGa2(C4O6H4)(4)(OH)(2)]center dot 4H(2)O, [ZnGa2(NH2CH2COOH)(4.5)](NO3)(8)center dot 4H(2)O and [ZnGa2(CO(NH2)(2))(7)](NO3)(8)center dot 9H(2)O have been synthesized and characterized by IR and UV-vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm-450 nm. (C) 2009 Elsevier B.V. All rights reserved.

109. Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Authors: Secu, M; Secu, CE; Polosan, S; Aldica, G; Ghica, C

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1872, DOI: 10.1016/j.jnoncrysol.2009.04.062

Transparent oxyfluoride glass-ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. (C) 2009 Elsevier B.V. All rights reserved.

110. Fe-catalyzed carbon nanotubes growth on fluidized powders by remote radiofrequency plasma beam

Authors: Vizireanu, S; Stoica, D; Birjega, R; Ghica, C; Teodorescu, V; Nistor, L; Ganea, R; Dinescu, G

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2060, DOI:

The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.

111. Revealing nanoscale structural TEM/HRTEM. Application on ferroelectric ordering by PMN-PT relaxor ferroelectric

Authors: Ghica, C; Nistor, L; Van Tendeloo, G

Published: SEP 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2333, DOI:

Nano-scale ordering may be revealed in transmission electron microscopy (TEM) by at least three techniques that will be presented in this work: selected area electron diffraction, conventional TEM and high-resolution TEM. Digital image processing is used to extract additional information from the high-resolution micrographs. The described methods are illustrated in a microstructural and compositional study of a 90%Pb(Mg1/3Nb2/3)O-3-10%PbTiO2 ceramic sample. High-resolution images reveal the presence of ordered compositional nano-domains, observable in two specific crystallographic orientations. Antiphase boundaries lying in the (111) planes separate them, while (100) and (111) facets separate the ordered domains from the disordered matrix.

112. Influence of polyvinylpyrolidone as an additive in electrochemical preparation of ZnO nanowires and nanostructured thin films

Authors: Enculescu, I; Matei, E; Sima, M; Enculescu, M; Sima, M; Ghica, C

Published: MAR-APR 2008, SURFACE AND INTERFACE ANALYSIS, 40, 560, DOI: 10.1002/sia.2749

Preparation of ZnO in different nano-morphological forms became a hot topic during the last few years. This tendency was motivated by the wide field of potential applications ranging from optics to electronics and spintronics. In the present work, we deal with the preparation of ZnO nanowires and nanostructured thin films using electrochemical deposition. ZnO nanowires were grown using the template approach, namely by replicating the nanopores of polycarbonate ion track membranes. The method yields uniform arrays of nanowires with the morphology controlled by the shape and size of the templates pores. Adding polyvinylpyrolidone as an additive in the growth bath became a necessity due to the fact that polycarbonate ion track membranes are usually hydrophobic and thus filling of the nanopores with the growth electrolyte is rather difficult. In order to better understand the influence of the additive on the electrochemical deposition of such nanostructures, similar experiments were performed for the deposition of ZnO thin films. Scanning electron microscopy, X-ray diffraction and optical spectroscopy measurements were performed for characterization of the deposited structures. Copyright (c) 2008 John Wiley & Sons, Ltd.

113. Dual behavior of gold nanoparticles, as generators and scavengers for free radicals

Authors: Ionita, P; Spafiu, F; Ghica, C

Published: OCT 2008, JOURNAL OF MATERIALS SCIENCE, 43, 6574, DOI: 10.1007/s10853-008-2987-1

114. Electrochemical growth and characterization of nanostructured ZnO thin films

Authors: Ghica, C; Enculescu, I; Nistor, LC; Matei, E; Van Tendeloo, G

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3240, DOI:

ZnO is a wide band-gap (ca. 3.4 eV) semiconductor, piezoelectric, pyroelectric, biocompatible, transparent in the visible spectrum and UV light emitting material. The fabrication in 2001 of the first nanobelts of semiconductor oxide materials lead to a rapid expansion of researches concerning one dimensional nanostructures (nanotubes, nanowires, nanobelts), given their possible application in optics, optoelectronics, piezoelectricity, catalysis. Researches carried on up to date evidenced the possibility to obtain an extraordinary variety of ZnO nanostructures, in function of the experimental parameters and the used growth methods. In this work we present morphostructural results on nanostructured ZnO layers obtained by electrochemical deposition. The films have been grown on gold covered glass plates and Si wafers, in various experimental conditions such as: nature of the wetting agents, electrical polarization of the substrate (continuous, pulsed). The influence of the growth conditions on the crystalline structure and morphology of the films is revealed by scanning and transmission electron microscopy studies. The films show a variety of growth morphologies, from entangled-wires-like to honeycomb-like layers. These large-specific-surface layers will be tested as nanostructured substrates for photovoltaic cells with improved efficiency.

115. Functional ZnO thin films obtained by radiofrequency beam assisted pulsed laser deposition

Authors: Epurescu, G; Scarisoreanu, ND; Matei, DG; Dinescu, G; Ghica, C; Nistor, LC; Dinescu, M

Published: 2008, ROMANIAN REPORTS IN PHYSICS, 60, +, DOI:

Piezoelectric and p type semiconductor ZnO thin films were deposited by radiofrequency beam assisted pulsed laser deposition. Optical, electrical and structural properties were found to depend on both deposition parameters and radiofrequency beam characteristics.

116. Hybrid metal (gold)-inorganic (silica) nanoparticles: Synthesis, characterization, and spin-labeling

Authors: Ionita, P; Ghica, C; Caproiu, MT; Ionita, G

Published: SEP 2008, JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS, 18, 419, DOI: 10.1007/s10904-008-9210-3

Water-soluble gold nanoparticles, capped with captopril, have been synthesized and characterized. Their average size is 2.3 nm, with a spherical shape. These gold nanoparticles can be easily labeled with stable free radicals (4-amino-tempo) by a coupling reaction performed in the presence of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ). Both synthesized and spin-labeled gold nanoparticles can be incorporated into much bigger (100 nm) silica nanoparticles using the Stober method, thus forming hybrid metal (gold)-inorganic (silica) nanoparticles. These hybrid silica nanoparticles (containing or not spin-labeled gold nanoparticles) can be easily spin-labeled with another stable free radical (4-isocyanato-tempo), leading to the formation of a double spin-labeled material. In this way, some stable free radicals are attached on the gold surface while others are attached on the silica surface. Three types of EPR spectra were recorded and discussed for the hybrid gold-silica nanoparticles: (1) where the spin labels are attached to the embedded gold nanoparticles, (2) where the spin labels are attached to the silica nanoparticles, and (3) in the case of the double spin labeled material where both gold and silica nanoparticles are spin-labeled. Influence of different solvents on the EPR spectra is also discussed.

117. Probing cellulose wettability by electron paramagnetic resonance

Authors: Ionita, G; Ghica, C; Ionita, P

Published: 2007, MATERIALS SCIENCE-POLAND, 25, 1017, DOI:

Carboxymethyl-cellu lose has been labelled with a stable free radical by reaction with 4-aminotempo in the presence of a coupling agent (EEDQ). The spin-labelled cellulose is highly stable, no leaking being noticed after months at room temperature. EPR spectroscopy was used as a main tool to study the wettability of such a material. The EPR spectrum of the dry spin-labelled cellulose shows the expected anisotropy, while addition of several solvents (acetone, ethyl acetate, DCM, methanol, toluene, PEG 200) induces the splitting of the spectrum into a two component system. Thus, the EPR spectrum is composed of a mobile component superimposed onto an immobilized one. Addition of water leads to a monocomponent isotropic spectrum. These data clearly indicate the presence of two types of sites to which the spin-label is attached. Variable temperature EPR spectra showed that an increase of temperature results in an increase in the mobility of the spin-label. Deposition of plain or spin-labelled gold nanoparticles on the cellulose fibres also affects the structure of the polymeric chain, as seen by changes in the EPR spectra.

118. Preparation of metallic nanowires with magnetic properties using the template method

Authors: Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

119. TEM characterization of extended defects induced in Si wafers by H-plasma treatment

Authors: Ghica, C; Nistor, LC; Bender, H; Richard, O; Van Tendeloo, G; Ulyashin, A

Published: JAN 21 2007, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 40, 400, DOI: 10.1088/0022-3727/40/2/016

Silicon hydrogenation is nowadays studied with the aim of developing and improving a technological method known as 'smart cut' used in the fabrication of 'silicon-on-insulator' devices. The goal of our study is to characterize the defects induced in silicon wafers after exposure to hydrogen RF plasma. Si < 001 > wafers have been treated at 250 degrees C under hydrogen RF plasma at 110 MHz, for various durations. The main features observed by transmission electron microscopy (TEM) are surface roughening and the presence of three kinds of defects: {111} planar defects, {100} planar defects and H bubbles. In this work a study using conventional TEM and high resolution transmission electron microscopy (HRTEM) techniques is presented on H bubbles and {100} planar defects induced in Si wafers by H-plasma treatment. The strain field around the defects is qualitatively characterized by diffraction contrast analysis and quantitatively by the geometrical phase method, by processing the HRTEM images.

120. Nanocrystalline Er : YAG thin films prepared by pulsed laser deposition: An electron microscopy study

Authors: Stanoi, D; Popescu, A; Ghica, C; Socol, G; Axente, E; Ristoscu, C; Mihailescu, IN; Stefan, A; Georgescu, S

Published: JUL 31 2007, APPLIED SURFACE SCIENCE, 253, 8272, DOI: 10.1016/j.apsusc.2007.02.113

We report the synthesis of well crystallized stoichiometric Er:YAG thin films by pulsed laser deposition from Er:YAG targets in low pressure oxygen, followed by a post-deposition treatment at 1400 degrees C in environmental air for 19 h. The structure and morphology of the films were examined by transmission electron microscopy and selected area electron diffraction. We demonstrated that the subsequent application of pulsed laser deposition and heat treatment resulted in the formation of well crystallized single phase cubic Er:YAG nanostructured coatings. (c) 2007 Elsevier B.V. All rights reserved.

121. Varieties of nanostructured carbon grown by expanding radiofrequency plasma beam

Authors: Vizireanu, S; Mitu, B; Dinescu, G; Nistor, L; Ghica, C; Maraloiu, A; Stancu, M; Ruxandra, G

Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1652, DOI:

Results regarding the growth of carbon nanostructures by using a low-pressure expanding radiofrequency plasma jet are reported. The growth was performed in an argon plasma injected with acetylene precursor, in the presence of ammonia or hydrogen, on a substrate covered with nickel or cobalt catalysts. Various forms of nanostructured carbon material were obtained, depending on the catalyst size, ammonia or hydrogen / acetylene ratio and substrate temperature. The results exemplified in the paper describe nickel nanoparticles coated in highly ordered graphite shells, granular carbon, two dimensional carbon nanoflakes, nanowires and nanorods.

122. P-type ZnO thin films grown by RF plasma beam assisted Pulsed Laser Deposition

Authors: Epurescu, G; Dinescu, G; Moldovan, A; Birjega, R; Dipietrantonio, F; Verona, E; Verardi, P; Nistor, LC; Ghica, C; Van Tendeloo, G; Dinescu, A

Published: JUL-DEC 2007, SUPERLATTICES AND MICROSTRUCTURES, 42, 84, DOI: 10.1016/j.spmi.2007.04.072

The high exciton binding energy and band gap energy of ZnO thin films open the prospect of fabricating semiconductor lasers in the ultraviolet spectral range. A prerequisite for laser diode fabrication is highly p-doped ZnO which was not reproducibly obtained up to now. Without intentional doping ZnO exhibits n-type conduction. ZnO thin films have been obtained by radio-frequency assisted pulsed laser deposition. A metallic Zn target was used for ablation in an oxygen and nitrogen RF discharge. The electrical and morphological properties of the films grown on Si were studied by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), optical absorption and Hall Effect measurements for different ratios between the nitrogen and oxygen content. The AFM images of the as grown ZnO films reveal high quality surfaces with low values for the surface roughness and a sharp distribution of grains sizes as an effect of the RF discharge. The XRD patterns for all samples exhibit only (002) and (004) peaks indicating that the c-axis is always oriented normal to the substrate surface. The films present p-type conductivity with different carrier concentration and mobility depending on the nitrogen/oxygen ratio. (c) 2007 Elsevier Ltd. All rights reserved.

123. Paramagnetic silica-coated gold nanoparticles

Authors: Ghica, C; Ionita, P

Published: DEC 2007, JOURNAL OF MATERIALS SCIENCE, 42, 10064, DOI: 10.1007/s10853-007-1980-4

Water soluble gold nanoparticles, obtained by the reduction of the gold (III) chloride with sodium borohydride in the presence of citric acid or thioctic acid, were covered with a paramagnetic silica layer using the Stober method, yielding a hybrid metallic-inorganic nanomaterial (gold nanoparticles, with an average size of 5 nm, embedded into silica nanoparticles, with an average size of 100 nm). The paramagnetic silica layer was formed by copolymerization of a paramagnetic silica precursor (derived from 3-aminopropyltrimethoxysilane) with tetramethyorthosilicate. The paramagnetic silica precursor was obtained by coupling 3-aminopropyltrimethoxysilane with 3-carboxy-proxyl free radical. TEM pictures show that each silica nanoparticle of about 100 nm in size embedded about 10 gold nanoparticles. These hybrid nanoparticles are quite stable and exhibit the expected paramagnetic characteristics, as seen by electron paramagnetic resonance. The accessibility of methanol through the silica layer was also studied. Depending on the capping ligands of the gold nanoparticles (citric or thioctic acid), different silica networks are formed, as seen by the mobility of the spin-label inside the silica layer. The EPR spectra showed that the paramagnetic silica layer is very robust and the mobility of the spin-probe inside the silica layer is very little affected by methanol. However, if spin-labeled thioctic acid protected gold nanoparticles were used in the material synthesis, the mobility of the spins attached to the gold surface is quite high in the presence of methanol, while the spins embedded into the silica layer remains immobilized.

124. Mesoseopic ordering in the 0.9 Pb(Mg1/3Nb2/3)O-3-0.1 PbTiO3 relaxor ferroelectric: a HRTEM study

Authors: Nistor, LC; Ghica, C; Van Tendeloo, G

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673753

We report a microstructural and compositional study of a 90% Pb(Mg1/3Nb2/3)O-3 - 10% PbTiO3 ceramic sample. High resolution transmission electron microscopy (HRTEM) revealed the presence of compositional ordered nano-domains (1 - 4 mn), observable in two specific orientations, [0 (1) over bar 1] and [1 1 (2) over bar]. However, the visibility and the ordering degree of the nano-domains on the HRTEM images are not at all obvious. Fourier filtering of the images clearly revealed the ordered domains. Antiphase boundaries lying in the (111) planes separate them, while (100) and (111) facets separate the ordered domains from the disordered matrix. Their shape is plate-like, not uniformly spread in the disordered matrix. Their average size varies in different regions of the sample, most probably due to a non-uniform distribution of Ti, as observed by energy dispersive X-ray spectroscopy. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

125. EPR and TEM characterization of electrolurninescent Alq(3)

Authors: Grecu, MN; Ghica, C; Mirea, A; Grecu, VV; Schwoerer, M

Published: 2006, ADVANCED MATERIALS FORUM III, PTS 1 AND 2, 514-516, 137, DOI: 10.4028/www.scientific.net/MSF.514-516.133

EPR and TEM investigations on sublimated solid Alq(3), [tris(8-hydroxyquinoline)aluminum(Ill)] are reported. Different paramagnetic centers in microcrystalline Alq3 fractions as synthesized and annealed are observed. Their nature, thermal treatment dependence, as well as correlation with the crystal structure are analyzed. The existence of randomly oriented triplets and quartets in annealed Alq3 fractions is evidenced from the temperature dependence of X- and Q-band EPR spectra. The spin Hamiltonian parameters are given and proposals for the model structures are made.

126. Femtosecond pulse shaping for phase and morphology control in PLD: Synthesis of cubic SiC

Authors: Ristoscu, C; Socol, G; Ghica, C; Mihailescu, IN; Gray, D; Klini, A; Manousaki, A; Anglos, D; Fotakis, C

Published: APR 30 2006, APPLIED SURFACE SCIENCE, 252, 4862, DOI: 10.1016/j.apsusc.2005.07.099

Pulse shaping introduces the method that makes possible the production of tunable arbitrary shaped pulses. We extend this method to control the prevalent growth of cubic SiC films on Si (10 0) substrates by pulsed laser deposition at temperatures around 973 K from a SiC target in vacuum. We used a laser system generating 200 fs pulses duration at 800 nm with 600 mu J at 1 kHz. The obtained structures are investigated by electron microscopy, X-ray diffraction and profilometry. We observed grains embedded in an amorphous texture, characteristic in our opinion to the depositions obtained with very short pulses. We present a comparison of deposited films with and without pulse shaping. Pulse shaping promotes increased crystallization and results in the deposition of thin structures of cubic SiC with a strongly reduced density of particulates, under similar deposition conditions. (c) 2005 Elsevier B.V. All rights reserved.

127. Growth and characterization of beta-SiC films obtained by fs laser ablation

Authors: Ghica, C; Ristoscu, C; Socol, G; Brodoceanu, D; Nistor, LC; Mihailescu, IN; Klini, A; Fotakis, C

Published: APR 30 2006, APPLIED SURFACE SCIENCE, 252, 4677, DOI: 10.1016/j.apsusc.2005.07.087

We achieved the growth of cubic silicon carbide (SiC) films on (100)Si substrates by pulsed laser deposition (PLD) at moderate temperatures such as 750 degrees C, from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The morphology of deposited films is dominated by columns nucleated from a thin nanostructured beta silicon carbide (beta-SiC) interface layer. The combined effects of columnar growth, tilted facets of the emerging columns and the presence of particulates on the film surface, lead to a rather rough surface of the films. (c) 2005 Elsevier B.V. All rights reserved.

128. Characterization of {111} planar defects induced in silicon by hydrogen plasma treatments

Authors: Ghica, C; Nistor, LC; Bender, H; Richard, O; Van Tendeloo, G; Ulyashin, A

Published: NOV 11 2006, PHILOSOPHICAL MAGAZINE, 86, 5151, DOI: 10.1080/14786430600801443

Microstructural characterization by transmission electron microscopy of the {111} planar defects induced in Si by treatment in hydrogen plasma is discussed. The {111} defects are analyzed by conventional ( TEM) and high-resolution transmission electron microscopy (HRTEM). Quantitative image processing by the geometrical phase method is applied to the experimental high-resolution image of an edge-on oriented {111} defect to measure the local displacements and strain field around it. Using these data, a structural model of the defect is derived. The validity of the structural model is checked by high-resolution image simulation and comparison with experimental images.

129. Nanostructure and properties of Pb(Zr,Ti)O-3-Pb(Ni-1/3 Nb-2/3)O-3 piezoceramics

Authors: Dimitriu, E; Craciun, F; Ghica, C; Ramer, R

Published: SEP 2005, JOURNAL DE PHYSIQUE IV, 128, 143, DOI: 10.1051/jp4:2005128022

Piezoceramics with composition 0.46 Pb(Zr0.3Ti0.7)O-3 - 0.53 Pb(Ni1/3Nb2/3)O-3 have been synthesized by solid-state reaction at different temperatures. The density varied between 8.05-8.1 g/cm(3). The sintered samples have been chemically electroded with Ni and poled at 220C under an electric field of 3 kV/cm. The XRD spectra confirmed the formation of tetragonal crystalline phase with a tetragonal distortion c/a = 1.0125 which was decreased from a value of about 1.042 that corresponds to pure PZT with y = 0.3. Some minor traces of non-reacted precursor oxides such as Nb2O5 have been also found. TEM results confirmed the formation of tetragonal phase and revealed crystal grains with domains of different size, slightly disoriented from each other. Dielectric measurements performed between 20 degrees C and 300 degrees C at different frequencies between 100 Hz and 1 MHz revealed a broad dielectric anomaly at T-m = 118 degrees C (200Hz) which shifts to 127 degrees C at I MHz driving frequency. A dependence of T-m on sintering temperature has been observed. A thermal hysteresis is also found on heating and cooling. This shows that the samples present both relaxor and ferroelectric characteristics. High values of the dielectric constant are found both at room temperature (about 5000) and at T-m (about 18000). The dependence of dielectric and piezoelectric constants on sintering temperature has been found.

130. Properties of ZnO thin films prepared by radio-frequency plasma beam assisted laser ablation

Authors: Scarisoreanu, N; Matei, DG; Dinescu, G; Epurescu, G; Ghica, C; Nistor, LC; Dinescu, M

Published: JUL 15 2005, APPLIED SURFACE SCIENCE, 247, 525, DOI: 10.1016/j.apsusc.2005.01.140

Zinc oxide thin films were obtained by laser ablation of a Zn target in oxygen reactive atmosphere, the oxygen being supplied either by a standard gas inlet valve or from a radio-frequency (rf) oxygen plasma. Pt-coated silicon and MgO were used as substrates. The influence of the deposition parameters as laser wavelength (266, 355, 1064 nm), laser fluence (1.5-20 J/cm(2)) and oxygen pressure (1-60 Pa) was studied. The influence of the rf plasma beam addition on the morphological proprieties of zinc oxide films was particularly investigated, simultaneously with several configurations of the direction of the ablation plasma, the rf plasma beam and the substrate. The obtained films, with thicknesses in the range of 50 nm to 1 mu m have been characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM). (c) 2005 Elsevier B.V. All rights reserved.

131. Microstructural characterization of polycrystalline Alq(3) grown by sublimation

Authors: Ghica, C; Grecu, MN; Gmeiner, J; Grecu, VV

Published: DEC 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 3003, DOI:

A microstructural investigation on polycrystalline electroluminescent Alq(3) obtained by train sublimation method is reported in the paper. The morphology and crystalline structure of the obtained Alq3 phases have been analyzed by transmission electron microscopy performed on samples collected from 3 different regions along the sublimation tube.

132. Growth and characterization of a-axis textured ZnO thin films

Authors: Nistor, LC; Ghica, C; Matei, D; Dinescu, G; Dinescu, M; Van Tendeloo, G

Published: APR 15 2005, JOURNAL OF CRYSTAL GROWTH, 277, 31, DOI: 10.1016/j.jcrysgro.2004.12.162

Smooth a-axis oriented ZnO thin films are grown on (001) MgO substrates by pulsed laser deposition assisted by a very directional radio frequency oxygen plasma. The structure of the film is examined by X-ray diffraction, electron diffraction and high resolution electron microscopy. The film grows with vertical columns and is highly textured. Two preferential orientation relations between the ZnO film and the MgO substrate are observed: (10010)(ZnO) vertical bar vertical bar (002)(MgO); [0002](ZnO)vertical bar vertical bar[2 0 0](MgO) and (1010)(ZnO) vertical bar (002)(ZnO) vertical bar vertical bar [200](MgO) [1210](MgO). The film/substrate interface is flat and strained because of the rather large lattice mismatch between the (1010) plane of ZnO and the (002) plane of MgO. (c) 2005 Elsevier B.V. All rights reserved.

133. Strain mapping around dislocations in diamond and cBN

Authors: Willems, B; Nistor, LC; Ghica, C; Van Tendeloo, G

Published: SEP 2005, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202, 2228, DOI: 10.1002/pssa.200561923

Strain fields around dislocations in diamond and cBN have been quantitatively characterized at a sub nanometer scale. The combination of experimental high resolution electron microscopy (HREM) and image analysis using the geometric phase method provides an accurate determination of the local deformations and strain. The results of the strain analysis of the 60 degrees perfect dislocation in diamond and cBN are discussed. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

134. Paramagnetic defect centres in crystalline Alq(3)

Authors: Grecu, MN; Mirea, A; Ghica, C; Colle, M; Schwoerer, M

Published: OCT 5 2005, JOURNAL OF PHYSICS-CONDENSED MATTER, 17, 6283, DOI: 10.1088/0953-8984/17/39/012

X- and Q-band electron paramagnetic resonance (EPR) investigation of different crystalline Alq(3) (tris(8-hydroxyquinoline)aluminium (III)) fractions formed by a train sublimation method are reported. Several paramagnetic defect centres corresponding to 1/2, 1, and 3/2 spin are observed at room temperature. Their intensity is dependent on the temperature, nature of the crystalline phase, and preparation conditions. Spectra simulation and analysis based on the spin Hamiltonian appropriate to a high spin system (S >=, 1) suggest the existence of randomly oriented triplets and quartets in annealed Alq(3) fractions. The crystalline Alq(3) phases responsible for the EPR powder spectra have been identified by transmission electron microscopy measurements performed on these sample fractions.

135. Modification of polyester track membranes by plasma treatments

Authors: Lazea, A; Kravets, LI; Albu, B; Ghica, C; Dinescu, G

Published: OCT 1 2005, SURFACE & COATINGS TECHNOLOGY, 200, 533, DOI: 10.1016/j.surfcoat.2005.01.120

The modification of the polyester track membranes by treatment in radiofrequency plasma generated by capacitive coupled parallel plate discharge in air and ammonia was studied. The investigation of the surface properties (roughness, pore size distribution, contact angle) before and after the plasma treatments was performed. The treatment resulted in increase of the surface roughness and of the pores effective diameter and change of wettability. Membranes presenting lower or higher contact angles, as compared with the initial one can be obtained by selecting adequate values for the radiofrequency power and treatment time values. (c) 2005 Elsevier B.V. All rights reserved.

136. Pulsed laser deposition of biocompatible polymers: a comparative study in case of pullulan

Authors: Cristescu, R; Stamatin, I; Mihaiescu, DE; Ghica, C; Albulescu, M; Mihailescu, IN; Chrisey, DB

Published: APR 1 2004, THIN SOLID FILMS, 453, 268, DOI: 10.1016/j.tsf.2003.11.145

We report some results of a comparison between thin films of pullulan biopolymer obtained by pulsed laser deposition (PLD) and matrix-assisted pulsed laser evaporation (MAPLE). In experiments we used a KrF* laser source generating pulses of 248 nm and 20 ns pulse duration. We demonstrate by Fourier transformed infrared spectroscopy (FTIR) that MAPLE is more appropriate than conventional PLD for transfer with high structural fidelity of biopolymers from target to substrate. In case of MAPLE, besides FTIR spectra, atomic force microscopy micrographs and scanning electron microscopy images prove that the film composition and structure strongly depend on the solvent used for the targets preparation: distilled water, ethylene glycol, ethanol, tert-butanol and dimethyl sulfoxide. Our best results for pullulan deposition were obtained using dimethyl sulfoxide as a solvent. This is the first report of successful MAPLE deposition of this material as thin films. (C) 2003 Elsevier B.V. All rights reserved.

137. Piezoelectric and optical properties of Sr-doped PT-PZ-Pb(Mg1/3Nb2/3)O-3 ceramics

Authors: Dimitriu, E; Ramer, R; Ghica, C; Iuga, A; Ghiordanescu, V

Published: 2004, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 24, 1708, DOI: 10.1016/S0955-2219(03)00478-3

Ceramics in the ternary system (Pb,Sr)TiO3-PbZrO3-Pb(Mg1/3Nb2/3)O-3, in the ratio 85.976/5.817/8.207 mol%, was prepared by mixed oxide route. With about 13.98 at % Sr+2, as isovalent substitution in A-position of the lead titanate, high-density samples were obtained for the sintering temperatures of about 1220 and 1230 degreesC. Tetragonal phases were identified both by XRD method and selected area electron diffraction pattern (SAED). The lattice parameter ratio, c/a, of about 1.017 indicated a decrease of tetragonal distortion. The typical TEM micrographs showed domains of about 50 nm wide. The reflection spectra were recorded to prove the presence of the transition Ti+4 to Ti+3. The principal mechanical, electrical and electromechanical properties were discussed as a function of the sintering temperature. The variation of the relative constant with the temperature and frequency evidenced a relaxation-like behavior of this ternary system. By combining the ferroelectric and relaxor end member we tried to improve the piezoelectric properties of a ceramic with a high content of lead titanate, and to achieve a material with both piezoelectric and relaxor-like properties. (C) 2003 Elsevier Ltd. All rights reserved.

138. Deposition of hydroxyapatite thin films by Nd : YAG laser ablation: a microstructural study

Authors: Nistor, LC; Ghica, C; Teodorescu, VS; Nistor, SV; Dinescu, M; Matei, D; Frangis, N; Vouroutzis, N; Liutas, C

Published: NOV 2 2004, MATERIALS RESEARCH BULLETIN, 39, 2101, DOI: 10.1016/j.materresbull.2004.07.006

Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation lambda = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 degreesC and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at lambda = 335 nm laser wavelength and 300 degreesC substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP). (C) 2004 Elsevier Ltd. All rights reserved.

139. Densification and crystallization of SnO2 : Sb sol-gel films using excimer laser annealing

Authors: Sandu, CS; Teodorescu, VS; Ghica, C; Canut, B; Blanchin, MG; Roger, JA; Brioude, A; Bret, T; Hoffmann, P; Garapon, C

Published: MAR 15 2003, APPLIED SURFACE SCIENCE, 208, 387, DOI: 10.1016/S0169-4332(02)01412-5

We have successfully applied laser annealing to sol-gel deposited SnO2:Sb thin films in order to achieve their crystallization. The as-deposited films are quasi-amorphous and electrically non-conductive. After laser annealing they crystallize and become conductive. This paper presents a comparative study of the laser annealed films and shows the influence of the irradiation parameters on the crystallization process and the electrical behavior of the films. Our results are quite promising in view of applying this kind of treatment to films deposited on thermally sensitive substrates (e.g. polymers). (C) 2002 Elsevier Science B.V. All rights reserved.

140. Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Authors: Nelea, V; Pelletier, H; Iliescu, M; Werckmann, J; Craciun, V; Mihailescu, IN; Ristoscu, C; Ghica, C

Published: DEC 2002, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 13, 1173, DOI: 10.1023/A:1021150207350

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti-5Al-2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500-600 C. The UV-assisted PLD films were grown in (10(-2)-10(-1) Pa) oxygen directly on Ti-5Al-2.5Fe substrates heated at 500-600 degreesC. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6-7 and 150-170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca2P2O7, Ca2P2O9 and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed. (C) 2002 Kluwer Academic Publishers.

141. The stability of cadmium chalcogenide pigments in the process of laser cleaning of painted surfaces

Authors: Radvan, R; Popovici, N; Savastru, R; Ghica, C; Sava, F; Popescu, M

Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 902, DOI:

Pigments based on cadmium selenide sulphides and cadmium sulfides were analysed as regarding their structure and stability against the laser irradiation, a new technique for cleaning the painted surfaces in artwork restoration, The pulsed Nd:YAG laser radiation determines the effusion of some sulphur from the red pigment Cd(S,Se) and significant decrease of the average size of the crystallites. The color turns to dark red. For yellow pigment (CdS) no change of crystallite size was detected after laser irradiation.

142. The influence of the h-BN morphology and structure on the c-BN growth

Authors: Nistor, L; Teodorescu, V; Ghica, C; Van Landuyt, J; Dinca, G; Georgeoni, P

Published: MAR-JUL 2001, DIAMOND AND RELATED MATERIALS, 10, 1356, DOI: 10.1016/S0925-9635(00)00377-0

The morphology and structure of hexagonal graphitic BN (h-BN) powders with graphitization indices GI <5, used as precursors for the synthesis of cubic BN (c-BN) crystals, has been investigated by transmission electron microscopy in diffraction contrast and high resolution. We show that besides the GI, which is a general parameter for controlling the structural quality of h-EN ponders, some other microstructural features strongly influence the synthesis of c-BN. In our opinion, the high reactivity of some h-BN powders results from the presence of some nucleation centers for c-BN, observed at the edges of the h-BN particles. They are formed by a rearrangement of the graphitic (0002) planes by bending back, joining in pairs and forming locally nanoarches (half nanotubes). In these particular places, the nature of bonding locally turns towards sp(3), as in the case of c-BN, (C) 2001 Elsevier Science B.V. All rights reserved.

143. Influence of the deposition configuration on the composition, structure and morphology of La0.6Y0.07Ca0.33Mn3-delta thin films obtained by pulsed laser deposition

Authors: Ghica, C; Valeanu, M; Nistor, LC; Teodorescu, V; Sandu, C; Ristoscu, C; Mihailescu, IN; Werckmann, J; Deville, JP

Published: DEC 2001, INTERNATIONAL JOURNAL OF INORGANIC MATERIALS, 3, 1256, DOI: 10.1016/S1466-6049(01)00153-2

We present a structural and morphological study on La0.6Y0.07Ca0.33MnO3-delta (LYCMO) thin films deposited by laser ablation onto MgO-buffered silicon wafers using two deposition configurations named on-axis and off-axis. All thin films have been deposited at high temperatures in an oxygen atmosphere. A comparative study between the on-axis and off-axis samples is performed by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The films are polycrystalline and show a columnar morphology. The off-axis sample shows a better crystalline texture, although slight compositional variations have been found. (C) 2001 Elsevier Science Ltd. All rights reserved.

144. In situ transmission electron microscopy study of the silicidation process in Co thin films on patterned (001) Si substrates

Authors: Ghica, C; Nistor, L; Bender, H; Steegen, A; Lauwers, A; Maex, K; Van Landuyt, J

Published: MAR 2001, JOURNAL OF MATERIALS RESEARCH, 16, 708, DOI: 10.1557/JMR.2001.0121

The results of an in situ transmission electron microscopy study of the formation of Co-silicides on patterned (001) Si substrates are discussed. It is shown that the results of the in situ heating experiments agreed very well with the data based on standard rapid thermal annealing experiments. Fast heating rates resulted in better definition of the silicide lines. Also, better lines were obtained for samples that received already a low-temperature ex situ anneal. A Ti cap layer gave rise to a higher degree of epitaxy in the CoSi2 silicide.

145. Structural investigation of a La0.6Y0.07Ca0.33MnO3 thin film by high resolution transmission electron microscopy

Authors: Ghica, C; Nistor, LC; Teodorescu, VS; Valeanu, M; Ristoscu, C; Mihailescu, IN; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 72, DOI:

The morphology and structure of a La0.6Y0.07Ca0.33MnO3 thin film is studied by transmission electron microscopy. The film was grown by pulsed laser deposition (PLD) on an MgO-buffered silicon <100> wafer. The as-deposited films are polycrystalline and show a columnar morphology. We present a detailed high-resolution transmission electron microscopy structural study concerning a possible monoclinic distortion of the orthorhombic LYCMO crystal cell. (Received February 22, 2000; accepted March 10, 2000).

146. Sr-ferrite thin films grown on sapphire by pulsed laser deposition

Authors: Koleva, ME; Zotova, S; Atanasov, PA; Tomov, RI; Ristoscu, C; Nelea, V; Chiritescu, C; Gyorgy, E; Ghica, C; Mihailescu, IN

Published: DEC 15 2000, APPLIED SURFACE SCIENCE, 168, 113, DOI: 10.1016/S0169-4332(00)00612-7

High-quality epitaxial strontium-hexaferrite (SrFe12O19) thin films were grown by pulsed laser deposition (PLD) on c-cut sapphire using KrF* excimer laser at a fluency of 2 J/cm(2) and substrate temperature of 800 degreesC in 100 mTorr oxygen environment. The X-ray diffraction (XRD) and morphology analyzes showed films with excellent crystalline structure and Aat surface. The thickness was found to influence considerably the surface morphology and magnetic properties of the as-deposited films. The highest orientation and the best morphology with smooth surface and fine grain structure was obtained for the him having a thickness of 750 nm. The highest coercive force of 1453 Oe was measured for this film in perpendicular to the plane direction. (C) 2000 Elsevier Science B.V. All rights reserved.

147. Pulsed laser deposition of hydroxyapatite thin films on Ti-5A1-2.5Fe substrates with and without buffer layers

Authors: Nelea, V; Ristoscu, C; Chiritescu, C; Ghica, C; Mihailescu, IN; Pelletier, H; Mille, P; Cornet, A

Published: DEC 15 2000, APPLIED SURFACE SCIENCE, 168, 131, DOI: 10.1016/S0169-4332(00)00616-4

We present a method for processing hydroxyapatite (HA) thin films on Ti-5Al-2.5Fe substrates. The films were grown by pulsed laser deposition (PLD) in vacuum at room temperature, using a KrFdouble dagger excimer laser. The amorphous as-deposited HA films were recrystallized in ambient air by a thermal treatment at 550 degreesC. The best results have been obtained when inserting a buffer layer of ceramic materials (TiN, ZrO2 or Al2O3) The films were characterized by complementary techniques: grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), cross-section transmission electron microscopy (XTEM), SAED, energy dispersive X-ray spectroscopy (EDS) and nanoindentation. The samples with buffer interlayer preserve the stoichiometry are completely recrystallized and present better mechanical characteristics as compared with that without buffer interlayer. (C) 2000 Published by Elsevier Science B.V.

148. Structural comparison between La0.60Y0.07Ca0.33MnO3-delta bulk and pulsed laser deposited thin films

Authors: Teodorescu, VS; Nistor, LC; Valeanu, M; Ghica, C; Sandu, C; Mihailescu, IN; Ristoscu, C; Deville, JP; Werckmann, J

Published: MAR 2000, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 211, 60, DOI: 10.1016/S0304-8853(99)00713-1

This work is a comparative study of the structural and magneto-transport properties of La0.60Y0.07Ca0.33MnO3-delta (LYCMO) as bulk and thin film. The bulk samples were prepared by solid-state reaction between the corresponding metallic oxides mixed in stoichiometric ratios. The thin film was deposited by pulsed laser deposition on an MgO single crystal using an excimer laser. We show that the structure and stoichiometry of the bulk target are perfectly reproduced in the thin film. We measured the magnetoresistive effect on both the LYCMO pellet and the thin film by using the four-probe technique. The maximum of the MR effect is 680% on the polycrystalline thin film in a 2T magnetic field. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

149. Transmission electron microscopy study of thin films and surface implanted wafers of LiNbO3

Authors: Teodorescu, VS; Ghica, C; Blanchin, MG; Moretti, P

Published: JUN 1999, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 1, 48, DOI:

Thin films prepared by pulsed laser deposition and single crystal implanted LiNbO3 wafers used in optoelectronic technology were studied by transmission electron microscopy. The use of high electron beam density for high resolution imaging induced a decomposition effect in the implanted LiNbO3 lattice. It is shown that the most probable decomposition leads to the formation of NbO2 nuclei by a topotactic solid state reaction along the pseudo-cubic directions of the lithium niobate matrix. It is also shown that powdered LiNbO3 specimens or samples obtained by preparation of cross section of LiNbO3 thin films are more stable in the electron beam, compared with the samples obtained from implanted LiNbO3 wafers.

150. Growth of carbon nickel multilayer for X-ray-UV optics by RF reactive magnetron sputtering

Authors: Georgescu, G; Nelea, V; Ulmeanu, M; Ghica, C; Nastase, N

Published: JUL 1999, APPLIED SURFACE SCIENCE, 148, 146, DOI: 10.1016/S0169-4332(99)00219-6

Amorphous C/Ni superlattice films designed as normal-incidence reflector for 5 nm have been grown on float-glass substrates by magnetron sputter deposition in Ar discharge. A comprehensive set of characterization techniques has been applied: grazing X-ray reflection (0.154 nm), atomic force microscopy and transmission electron microscopy in order to determine the quality of the structure. By comparing the results, it could be concluded that RF-magnetron sputtering technique is a good choice for growing such layered synthetic microstructures. (C) 1999 Elsevier Science B.V. All rights reserved.

151. Characterization of carbon nitride thin films deposited by a combined RF and DC plasma beam

Authors: Dinescu, G; Aldea, E; Musa, G; van de Sanden, MCM; de Graaf, A; Ghica, C; Gartner, M; Andrei, A

Published: JUL 18 1998, THIN SOLID FILMS, 325, 129, DOI: 10.1016/S0040-6090(98)00509-4

Thin carbon nitride films have been deposited on silicon(100) substrates downstream of a nitrogen plasma beam generated in a combined RF (13.56 MHz, 40-50 W) and DC (voltage +/-200 V, power 1-10 W) discharge between a graphite electrode and a graphite nozzle. By combining the RF and DC sources the capability of rf field to create extended plasmas is used together with the enhanced sputtering and biasing effect of the DC source. The plasma characteristics (electron temperature, presence of molecular species) have been studied by optical emission spectroscopy. Deposition rates of 2.5-3 nm/s are obtained at the centre of the plasma beam and at a few centimetres distance from the nozzle. The films have been investigated by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, scanning and transmission electron microscopy, and microhardness measurements. The films have an overall N:C ratio of 0.28 but the distribution of different nitrogen bonds depends upon the DC bias conditions. In the spectral range 0.3-0.7 mu m the refractive index increases slightly from 1.5 to 2.2. The films are amorphous, with morphology consisting of a columnar structure. The columns have a diameter of about 20 nm. A hardness of 24 GPa has been measured. (C) 1998 Elsevier Science S.A. All rights reserved.

Dr. Corneliu GHICA

Scientific Researcher I

Education

Positions

Research interests

Expertize

Projects

1. Nanoscaled ferroelectric (pseudo)-binary oxide thin film supercapacitors for flexible and ultrafast pulsed power electronics (NanOx4Estor)

2. Interplay structure-functionality in the case of nanostructured materials for gas sensors by electron tomography and operando TEM

3. From 2D to 3D+ nanoscale characterization of advanced functional materials

4. Atomically resolved structure and interface related phenomena in nano-scale modulated smart materials

5. Laser processing of defects induced in silicon by RF plasma hydrogenation. Contribution to the development of the SOI technology.

Publications

1. Low traces of acetone detection with WO3-based chemical sensors

2. In-depth insight into the structural properties of nanoparticulate NiO for CO sensing

3. Phase transitions in ferroelectric ZrO2 thin films

4. Unlocking superior NO2 sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors

5. Surface properties, chemical reactivity, and ambient stability of cadmium diarsenide CdAs2, a topological chiral material hosting Kramers-Weyl fermions

6. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

7. High-performance and self-powered visible light photodetector using multiple coupled synergetic effects

8. Hydrogen Production Mechanism in Low-Temperature Methanol Decomposition Catalyzed by Ni3Sn4 Intermetallic Compound: A Combined Operando and Density Functional Theory Investigation

9. Cost-effective, high-performance Ni3Sn4 electrocatalysts for methanol oxidation reaction in acidic environments

10. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

11. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

12. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

13. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

14. Cost-effective, high-performance Ni3Sn4 electrocatalysts for methanol oxidation reaction in acidic environments

15. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

16. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

17. The influence of the synthesis method on Gd2O3 morpho-structural properties and sensitivity to CO2 under in-field conditions

18. Hydrogen Production Mechanism in Low-Temperature Methanol Decomposition Catalyzed by Ni3Sn4 Intermetallic Compound: A Combined Operando and Density Functional Theory Investigation

19. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

20. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

21. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

22. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

23. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

24. 3D Porous Collagen Matrices-A Reservoir for In Vitro Simultaneous Release of Tannic Acid and Chlorhexidine

25. Improving the Efficiency of Gallium Telluride for Photocatalysis, Electrocatalysis, and Chemical Sensing through Defects Engineering and Interfacing with its Native Oxide

26.NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 high-entropy layered oxide - experimental and theoretical evidence of high electrochemical performance in sodium batteries

27. Chitosan-Hyaluronan Nanoparticles for Vinblastine Sulfate Delivery: Characterization and Internalization Studies on K-562 Cells

28. Influence of relative humidity on CO2 interaction mechanism for Gd-doped SnO2 with respect to pure SnO2 and Gd2O3

29. NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 high-entropy layered oxide - experimental and theoretical evidence of high electrochemical performance in sodium batteries

30. Charge State Effects in Swift-Heavy-Ion-Irradiated Nanomaterials

31. Effects of Calcination Temperature on CO-Sensing Mechanism for NiO-Based Gas Sensors

32. Ferroelectric properties of ZrO2 films deposited on ITO-coated glass

33. All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films

34. Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors-The Influence of Humidity

35. Wake-up Free Ferroelectric Rhombohedral Phase in Epitaxially Strained ZrO2 Thin Films

36. New Phenotype and Mineralization of Biogenic Iron Oxide in Magnetotactic Bacteria

37. Nd-doped ZnO films grown on c-cut sapphire by pulsed-electron beam deposition under oblique incidence

38. Structure and water uptake in BaLnCo(2)O(6-delta) (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

39. Low temperature CO sensing under infield conditions with in doped Pd/SnO2

40. Perovskite ferroelectric thin film as an efficient interface to enhance the photovoltaic characteristics of Si/SnO(x)heterojunctions

41. Aminopropyl-silica functionalized with halogen-reactive compounds for antimicrobial applications

42. Energy storage performance of ferroelectric ZrO(2)film capacitors: effect of HfO2:Al(2)O(3)dielectric insert layer

43. HfO2-Al2O3 Dielectric Layer for a Performing Metal-Ferroelectric-Insulator-Semiconductor Structure with a Ferroelectric 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 Thin Film

44. HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

45. Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties

46. Nanoclustered Pd decorated nanocrystalline Zn doped SnO2 for ppb NO2 detection at low temperature

47. Bimodal mesoporous NiO/CeO2-delta-YSZ with enhanced carbon tolerance in catalytic partial oxidation of methane-Potential IT-SOFCs anode

48. Tailoring the Dopant Distribution in ZnO:Mn Nanocrystals

49. Hysteretic Characteristics of Pulsed Laser Deposited 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3/ZnO Bilayers

50. Ferroelectric photovoltaic characteristics of pulsed laser deposited 0.5Ba (Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3/ZnO heterostructures

51. A Study of Extended Defects in Surface Damaged Crystals

52. Wet chemical synthesis of ZnO-CdS composites and their photocatalytic activity

53. Full Tetragonal Phase Stabilization in ZrO2 Nanoparticles Using Wet Impregnation: Interplay of Host Structure, Dopant Concentration and Sensitivity of Characterization Technique

54. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

55. Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

56. Impact of thickness variation on structural, dielectric and piezoelectric properties of (Ba, Ca) (Ti, Zr)O-3 epitaxial thin films

57. Ferroelectric switching dynamics in 0.5Ba(Zr0.2Ti0.8)O-3-0.5( Ba0.7Ca0.3)TiO3 thin films

58. Lipoic acid functionalized SiO2@Ag nanoparticles. Synthesis, characterization and evaluation of biological activity

59. On the threshold for ion track formation in CaF2

60. Lipoic Acid Gold Nanoparticles Functionalized with Organic Compounds as Bioactive Materials

61. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates

62. Exploring porous nanosilica-TEMPO as heterogeneous aerobic oxidation catalyst: the influence of supported gold clusters

63. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

64. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

65. Fast atomic diffusion in amorphous films induced by laser pulse annealing

66. Atomic scale elemental mapping of light elements in multilayered perovskite coatings

67. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation

3. Phase transitions in ferroelectric ZrO₂ thin films

4. Unlocking superior NO₂ sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors

6. Fermiology of Chiral Cadmium Diarsenide CdAs₂, a Candidate for Hosting Kramers-Weyl Fermions

9. Cost-effective, high-performance Ni₃Sn₄ electrocatalysts for methanol oxidation reaction in acidic environments

10. Solution-processed In₂Se₃ nanosheets for ultrasensitive and highly selective NO₂ gas sensors

22. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO₂ Thin Films

23. Ferroelectric Orthorhombic ZrO₂ Thin Films Achieved Through Nanosecond Laser Annealing

26.
NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 high-entropy layered oxide - experimental and theoretical evidence of high electrochemical performance in sodium batteries