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Dr. Cristina Besleaga

Scientific Researcher I

Laboratory of Complex Heterostructures and Multifunctional Materials

cristina[DOT]besleaga[AT]infim[DOT]ro
Keywords: micro-electronics, opto-electronics, solar cells,

Education

Faculty of Physics, University of Bucharest, Romania

PhD thesis: "Wide band semiconductors with applications in transparent electronics" (2013)

Positions

Scientific researcher rank I

Awards

▪ In September 2014, the applicant won the best poster presentation award at the "10th International Conference on Physics of Advanced Materials" for the work entitled "Advanced characterization of amorphous oxide semiconductor thin films by X-ray reflectivity and thermally stimulated current spectroscopy".

▪ In 2016, the „Excelence” prize from ProInvent Exhibition of Inventions – XIV edition

▪ In  2018, „Ștefan Procopiu” prize from Romanian Academy (https://acad.ro/premiileAR/liste/2016.pdf);

▪ In 2019, „Young Researchers in Science and Engineering” offered by Dr. Rada Mihalcea and  Cluj-Napoca City Hall  (https://primariaclujnapoca.ro/evenimente/tinerii-cercetatori-premiul-pentru-stiinta-si-inginerie/). 

Research interests

  • Micro-electronics
  • Transport phenomena in semiconductors
  • Halide perovskite materials and its applications

Expertize

I work in the field of electronic and optoelectronic devices fabrication since 2008 and was member in the research team of more than 16 national and international scientific projects.

I have expertise in:

-       Synthesis of thin films by magnetron sputtering;

-       Characterization of thin film structures: structural (X-ray diffraction, X-ray reflectometry), morphological (atomic force microscope), optical (UV-Vis-IR spectroscopy), and electrical (resistivity/conductivity, Hall effect, dielectric spectroscopy);

-        Fabrication of electronic and optoelectronic devices in clean room conditions and their functional characterization: photovoltaic cells, metal-insulator-metal (MIM) structures, metal-insulator-semiconductor (MIS) structures, and thin film field effect transistors (TFT).

Demonstrated leadership capacities of research project coordination and budget administration; Project leader of:

▪ PN-II-RU-TE-2014-4-1122 „Field effect transistors based on new transparent heterostructures synthesized at low temperatures” project

▪ PN-III-P1-1.1-PD-2016-1546 “Lead-free halide perovskite photo-transistors as first step towards hybrid lead-free OLETs for next generation displays” project

▪ PN-III-P1-1.1-TE-2019-0688 “ High quality HZO and AlN films grown by industrially compatible techniques for next generation electronic and sensing devices”

▪ PN-III-P2-2.1-PTE-2021-0150, as National Institute of Materials Physics Responsible:  “Nanostructurated coating technology for self-cleaning and antibacterial windows”

▪ PN-IV-ERANET-M-3-ERANET-LightCell „Quasi-1D materials for advanced thin-film photovoltaics”PN-IV-ERANET-M-3-ERANET-LightCell „Quasi-1D materials for advanced thin-film photovoltaics”

Patents

▪ patent  BNP No.  RO132504-A2 /A00747/01-01-2016;  “Piroelectric detection element  for work at high temperatures”

▪ patent BND No.  A00427/15.07.2019; “ Antena planara de microunde cu geometrie noua a suprafetei radiante”

▪ patent BNA No.  A00364/2018; “ Strat mezoporos pentru celule solare pe bază de perovskiți și metoda de obținere” 

▪ patent BNP No.  A00439/2018; “ Procedeu de obținere a unui fotodetector pe bază de matrici de nanofire miez-coajă de tip oxid de cupru și oxid de zinc preparate pe electrozi metalici interdigitați”

▪ patent BNA No.  A00195/2017; “ Printer for successive deposition of ultra-thin layers of different physical-chemical properties”;

▪ patent BND No.  A00633/12.10.2020, “ Procedeu de realizare a unui implant endoosos cu activitate antimicrobiana extinsa, conditionata ca intensitate si durata prin grosimea stratului bioresorbabil de acoperire din sticla fosfatica cosubstituita”;

▪ patent BND No.  A00632/12.10.2020, “ Foto-tranzistor in strat subtire, pe baza de perovskite halogenati fara plumb, avand dioda ionica in rol de poarta si metoda de obtinere”;

▪ patent US No. US 10.902.914 B2/ 01.26.2021, “Programmable resistive memory element and a method of making the same”.

 

Resume

 

Born in 1986 in Romania, graduated the Faculty of Physics – Section “Medical Physics” at University of Bucharest - Romania (UB-FF) (2007), has a MSc degree in Solid-State Physics (UB-FF) (2010), and a PhD degree in Solid-State Physics (UB-FF) (2013), PhD thesis title:  Wide band semiconductors with application in transparent electronics.

 

Expertise:

-       Working in clean room: I graduated the “Quality Assurance in Terms of Cleanliness: Fundamentals of Cleanliness Technology and Clean Production” course delivered by Fraunhofer Institute for Manufacturing Engineering and Automation IPA, Stuttgart;

-       I have 12 years of experience in device processing in clean room condition;

-       I have extensive knowledge about physical vapor deposition of thin layers;

-       fabrication (processes carried out in clean room) of optoelectronic and micro-electronic devices: diodes, MIM, MIS, TFT, MEM;

-       command of highly-complex synthesis and characterization research/production systems: fabrication of thin films by magnetron sputtering; characterization of thin film structures: structural (X-ray diffraction, X-ray reflectometry), morphological (atomic force microscopy), optical (UV-Vis-IR spectroscopy), and electrical (resistivity/conductivity, Hall effect, dielectric spectroscopy).

 

Work experience:

·               National Institute of Materials Physics - Romania (NIMP; www.infim.ro) (2012 – to date);

·               Research & Development Centre for Materials, Electronics and Optoelectronic Devices (MDEO), Faculty of Physics, University of Bucharest – Romania (www.mdeo.eu) (2009-2012);

·               National Institute of Research & Development for Optoelectronics - Romania (INOE;  www.inoe.ro) (2008-2009).

·               I was part, as team member, in 26 research projects.

 

Managerial skills: demonstrated leadership capacities of research project coordination and budget administration; Project leader of:

 

4 national projects:

 

1.     PN-II-RU-TE-2014-4-1122 „Field effect transistors based on new transparent heterostructures synthesized at low temperatures” (2015 – 2017) – team of 7 people;

2.     PN-III-P1-1.1-PD-2016-1546 “ Lead-free halide perovskite photo-transistors as first step towards hybrid lead-free OLETs for next generation displays” (2018 – 2020) – team of 2 people;

3.     PN-III-P1-1.1-TE-2019-0688 “ High quality HZO and AlN films grown by industrially compatible techniques for next generation electronic and sensing devices” (2020 – 2022) -team of 9 people;

4.     As National Institute of Materials Physics Responsible: PN-III-P2-2.1-PTE-2021-0150 “Nanostructurated coating technology for self-cleaning and antibacterial windows” (2022-2024) – team of 7 people;

5.     As National Institute of Materials Physics Responsible: PN-IV-ERANET-M-3-ERANET-LightCell „Quasi-1D materials for advanced thin-film photovoltaics” (2024-2026) – team of 15 people.

 

1 international project:

6.     As National Institute of Materials Physics Responsible: PN-IV-ERANET-M-3-ERANET-LightCell „Quasi-1D materials for advanced thin-film photovoltaics” (2024-2026) – team of 15 people.

 

 

6 awarded patents:

-       patent US No. US 11.386.953-B2/2021: Programmable resistive memory element and a method of making the same;

-       RO134819-B1/2022: Process for making an endoosseous implant with extended antimicrobial activity, conditioned in intensity and duration by the thickness of the bioresorbable co-substituted phosphate glass coating layer;

-        RO132815-B1/2020: Mesoporous layer for halide perovskite-based solar cells and method of obtaining;

-       RO132595-B1/2019: The method of making osteointegrative implants covered with layers of bio-active glass, synthesized in magnetron plasma;

-       RO132082-B1/2019: Printer for depositing ultra-thin layers with different physico-chemical properties;

-       RO 132504 B1: Pyroelectric detection element for working at high temperatures.

 

Work stages:

-       at the University Nova de Lisboa– Portugal (Prof. Dr. Elvira Fortunato and Prof. Dr. Rodrigo Martins);

-       University of Oslo – Norway;

-       ARPES facility – Swiss;

-       CVD/ALD AnnealSys company – France.

Awards:

-       third prize „Young Researchers in Science and Engineering” offered by Dr. Rada Mihalcea and  Cluj-Napoca City Hall  (2019);

-       the „Excelence” prize and gold medal from Pro Invent Exhibition, Cluj-Napoca, XVII edition (2019);

-        „ Ștefan Procopiu” Romanian Academy award for contributions made in the field of photovoltaics (2018);

-       Gold medal from EUROINVENT, Iași (2018);

-       the „Excelence” prize and gold medal from „Ștefan cel Mare” University (2018); the „Excelence” prize from Pro Invent Exhibition, Cluj-Napoca, XIV edition (2016);

-       the best poster presentation award at the "10th International Conference on Physics of Advanced Materials" for the work entitled "Advanced characterization of amorphous oxide semiconductor thin films by X-ray reflectivity and thermally stimulated current spectroscopy (2014).

Publications: 53 articles published in Web of Science® (WoS) journals with impact factor (e.g., Appl Surf Sci, J Phys Chem Lett, Nanomaterials, Sol Energy, J Mater Chem C, Adv. Opt. Mater.); Hirsch index (WoS): 22; Citations (without self-citations): 1181.

 

 

Professional profile web-links: https://www.linkedin.com/in/besleaga-stan-cristina/; UEFISCDI ID (UEF-ID): U-1700-039E-3699; ORCID ID: 0000-0003-3311-869X; WoS ResearcherID: I-7862-2019. And G-5179-2012

Projects

1. Quasi-1D materials for advanced thin-film photovoltaics

Project Type: ERANET, Start Date: 2024-03-15 End Date: 2026-07-31

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2. High quality HZO and AlN films grown by industrially compatible techniques for next generation electronic and sensing devices

Project Type: TE, Start Date: 2020-09-14 End Date: 2022-11-30

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3. Lead-free halide perovskite photo-transistors as first step towards hybrid lead-free OLETs for next generation displays

Project Type: PD, Start Date: 2018-05-02 End Date: 2020-04-30

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4. Field effect transistors based on new transparent heterostructures synthesized at low temperatures (TRANSTEC)

Project Type: TE, Start Date: 2015-10-01 End Date: 2017-09-30

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Publications

Open Access
1. Effect of molecular adsorption on the conductivity of selectively grown, interconnected 2D-MoS2 atomically thin flake structures
Authors: Stavarache, I; Palade, C; Slav, A; Dascalescu, I; Lepadatu, AM; Matei, E; Besleaga, C; Ciurea, ML; Kardynal, BE; Stoica, T

Published: APR 8 2025, NANOSCALE ADVANCES, 7, DOI: 10.1039/d5na00138b

The gas sensitivity of field-effect structures with 2D-MoS2 channels selectively grown between Mo electrodes using the Mo-CVD method was investigated by measuring the effect of molecular adsorption from air on the device source-drain current (Isd). The channels were composed of interconnected atomically thin MoS2 grains, with their density and average thickness varied by choosing two different distances (15 and 20 mu m) between the Mo contacts. A high response to the tested stimuli, including molecule adsorption, illumination and gate voltage changes, was observed. A significant, persistent photoconduction was induced by positive charge accumulation on traps, most likely at grain boundaries and associated defects. Isd increased under high vacuum, both in the dark and under illumination. The relative dark current response to the transition from air to high vacuum reached up to 1000% at the turn-on voltage. When monitored during the gradual change in air pressure, Isd exhibited a non-monotonic function, sharply peaking at about 10-2 mbar, suggesting molecular adsorption on different defect sites and orientations of adsorbed H2O molecules, which were capable of inducing electron accumulation or depletion. Despite the screening of disorder by extra electrons, the #20 mu m sample remained more sensitive to air molecules on its surface. The high vacuum state was also investigated by annealing devices at temperatures up to 340 K in high vacuum, followed by measurements down to 100 K. This revealed thermally stimulated currents and activation energies of trapping electronic states assigned to sulfur vacancies (230 meV) and other shallow levels (85-120 meV), possibly due to natural impurities, grain boundaries or disorder defects. The results demonstrate the high sensitivity of these devices to molecular adsorption, making the technology promising for the easy fabrication of chemical sensors.
Open Access
2. Phase Transitions in Dimer/Layered Sb-Based Hybrid Halide Perovskites: An In-Depth Analysis of Structural and Spectroscopic Properties
Authors: Ciobotaru, IC; Ciobotaru, CC; Bartha, C; Enculescu, M; Secu, M; Polosan, S; Besleaga, C

Published: FEB 2025, ADVANCED OPTICAL MATERIALS, 13, DOI: 10.1002/adom.202402242

When used as the active layers-either as a light absorber in photovoltaic devices or as an electroluminescent material in light-emitting devices-lead-free perovskites significantly impact the performance of optoelectronic devices. This study focuses on antimony-based perovskites, which are promising for lighting applications. These types of perovskites enable the formation of self-trapped excitons (STEs) with higher dissociation energy than lead-based perovskites, which generate excitons with lower dissociation energy. The (CH3NH3)3Sb2I9 crystals are synthesized using two methods, resulting in distinct spatial configurations - dimer and dimer/layered mixtures, each exhibiting unique structural and spectroscopic properties, as revealed by comprehensive multi-parametric complementary analyses. Their emissive properties underscore the efficiency of the STE photoluminescence, driven by electron-phonon interactions and influenced by Sb-Sb distances in (CH3NH3)3Sb2I9 powder, whether dispersed in polymethyl-methacrylate or solution. The phase transition from monoclinic to hexagonal (dimer) and trigonal (layered) structures enabled the tuning of the optical properties in direct correlation with the structural and electrical features. The photoluminescence behavior of the STEs, analyzed in conjunction with the Raman spectroscopy, elucidates the dynamic process of the electron-phonon coupling effects in the dimer (face-capping Sb-I octahedra) and layered (corner-sharing Sb-I octahedra) crystallographic structures.
Open Access
3. Electron transporting bilayers for perovskite solar cells: Spray coating deposition of c-TiO2/m-SnO2-quantum dots
Authors: Mirea, AG; Vlaicu, ID; Derbali, S; Neatu, F; Tomulescu, AG; Besleaga, C; Enculescu, M; Kuncser, AC; Iacoban, AC; Filipoiu, N; Cuzminschi, M; Nemnes, GA; Manolescu, A; Florea, M; Pintilie, I

Published: JAN 20 2025, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 705, 135508, DOI: 10.1016/j.colsurfa.2024.135508

Herein we present a comparative study among different spray-coated nanometric mesoporous electron transporting layers (ETLs) in perovskite solar cells (PSC), namely m-TiO2, 2 , m-SnO2 2 and m-SnO2 2 quantum dots (mSnO2QDs). 2 QDs). The solutions used for deposition were prepared from commercial pastes and colloidal suspensions for m-TiO2 2 and m-SnO2. 2 . For m-SnO2QDs 2 QDs in-house QDs solutions were prepared. The formamidiniummethylamonium-potassium (FAMA@10 K) has been used as light absorber material in the fabricated PSCs. The structural, compositional and morphological studies, correlated with the photovoltaic performance of PSCs, indicate that the m-SnO2 2 QDs layer is the best candidate among the three investigated mesoporous ETLs. Compared with the suspensions used for the other two ETLs, the in-house prepared SnO2 2 QDs solution presents smaller agglomerates of nanoparticles and results in the formation of a thinner, more uniform and compact mesoporous ETL. The FAMA@10 K perovskite deposited on m-SnO2 2 QDs ETL presents a lower roughness, better uniformity and a higher amount of PbI2. 2 . Our work unveils that the SnO2 2 QDs solution can be easily produced in laboratory and when is deposited as mesoporous scaffold in a PSC with FAMA@10 K perovskite, the power conversion efficiency increases up to 14.90 %, being with up to 27 % larger than in the PSCs with m-TiO2 2 and mSnO2 2 ETLs prepared from commercial solutions. By modeling the J-V dynamic hysteresis with more than 90 % match between the calculated and experimental J-V data, for all three types of mesoporous ETLs, the relevant parameters that explain the hysteresis magnitude and account for ionic-induced recombination processes in PSCs were determined.
Open Access
4. Reticulated mesoporous TiO2 scaffold for self-cleaning surfaces
Authors: Besleaga, C; Tomulescu, AG; Zgura, I; Stepanova, A; Galca, AC; Laafar, S; Zorila, FL; Alexandru, M; Pintilie, I; Iliescu, M

Published: NOV 1 2024, CERAMICS INTERNATIONAL, 50, DOI: 10.1016/j.ceramint.2024.08.072

Interest in self-cleaning coatings is rising due to their potential to enhance comfort and quality of life in polluted urban environments, driving the search for materials with optimal physical properties. Convergent with this goal, this study investigates the wetting properties and photo-catalytic efficiency of reticulated TiO2 layers. It shows that these properties are significantly influenced by the topographical characteristics of the TiO2 surface, which can be precisely controlled through variations in pulverization pressure and low-temperature post-annealing treatments. Post-deposition annealing of the TiO2 layers achieves 100 % self-cleaning efficiency for both thick and thin films, with optical transmission ranging from approximately 60 %-80 % in the visible spectrum. Additionally, the TiO2 layers exhibited promising capabilities for eliminating pathogenic microorganisms and disinfecting surfaces. The underlying causal factors of these remarkable and technologically promising surface features are explored and discussed.
5. NANOSTRUCTURED LAYERS DEPOSITION FOR SELF-CLEANING GLASS
Authors: Iliescu, M; Besleaga, C; Nitu, C; Tomulescu, A; Pintilie, I; Melinte, O; Rosu, MM

Published: OCT 2023, ACTA TECHNICA NAPOCENSIS SERIES-APPLIED MATHEMATICS MECHANICS AND ENGINEERING, 66, DOI:

This paper evidences research results on a new technology for deposition of TiO2 nanostructured layers on glass. Air pollution, industrialization and everyday life activities are factors that point towards the need for efficient and ergonomic cleaning process of the impressive glazing surfaces that surround people in modern offices, leisure places and not the least, in houses. The design of equipment, the innovative technique based on pneumatically spraying a suspension of TiO2 nanocrystals, the process parameters and preliminary test results for the obtained layers stand as main topics for the article. Integration of the system into industry 4.0 virtual intelligent platform is also presented. Further research development in order to validate the nanostructured TiO2 coating on glazed surfaces is aimed.
Open Access
6. Bistable Boron-Related Defect Associated with the Acceptor Removal Process in Irradiated p-Type Silicon-Electronic Properties of Configurational Transformations
Authors: Nitescu, A; Besleaga, C; Nemnes, GA; Pintilie, I

Published: JUN 2023, SENSORS, 23, 5725, DOI: 10.3390/s23125725

The acceptor removal process is the most detrimental effect encountered in irradiated boron-doped silicon. This process is caused by a radiation-induced boron-containing donor (BCD) defect with bistable properties that are reflected in the electrical measurements performed in usual ambient laboratory conditions. In this work, the electronic properties of the BCD defect in its two different configurations (A and B) and the kinetics behind transformations are determined from the variations in the capacitance-voltage characteristics in the 243-308 K temperature range. The changes in the depletion voltage are consistent with the variations in the BCD defect concentration in the A configuration, as measured with the thermally stimulated current technique. The A & RARR;B transformation takes place in non-equilibrium conditions when free carriers in excess are injected into the device. B & RARR;A reverse transformation occurs when the non-equilibrium free carriers are removed. Energy barriers of 0.36 eV and 0.94 eV are determined for the A & RARR;B and B & RARR;A configurational transformations, respectively. The determined transformation rates indicate that the defect conversions are accompanied by electron capture for the A & RARR;B conversion and by electron emission for the B & RARR;A transformation. A configuration coordinate diagram of the BCD defect transformations is proposed.
Open Access
7. Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films
Authors: Stancu, V; Tomulescu, AG; Leonat, LN; Balescu, LM; Galca, AC; Toma, V; Besleaga, C; Derbali, S; Pintilie, I

Published: FEB 2023, COATINGS, 13, 378, DOI: 10.3390/coatings13020378

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K(0.1)FA(0.7)MA(0.2)PbI(2.8)Cl(0.2) (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV-vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA.
Open Access
8. Self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors
Authors: Costas, A; Florica, C; Preda, N; Besleaga, C; Kuncser, A; Enculescu, I

Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6834, DOI: 10.1038/s41598-022-10879-5

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.
Open Access
9. Capacitive and Inductive Effects in Perovskite Solar Cells: The Different Roles of Ionic Current and Ionic Charge Accumulation
Authors: Filipoiu, N; Preda, AT; Anghel, DV; Patru, R; Brophy, RE; Kateb, M; Besleaga, C; Tomulescu, AG; Pintilie, I; Manolescu, A; Nemnes, GA

Published: DEC 28 2022, PHYSICAL REVIEW APPLIED, 18, 064087, DOI: 10.1103/PhysRevApplied.18.064087

Dynamic hysteresis effects have been long known to occur in the current density-voltage characteristics of perovskite solar cells, with the ionic migration being identified as the primary factor. The hysteretic effects impacted early studies by the uncertainty in the evaluation of the power conversion efficiency, while currently, potential links to degradation mechanisms are the focus. Therefore, understanding ion migration is a central goal, typically addressed by performing a combined large and small signal analysis. The reported large capacitive and inductive effects created controversies with respect to the underlying mechanisms, yielding essentially two classes of models, one based on the large accumulation capacitances and the other based on the ionic modulation of the collected current. We introduce here an equivalent circuit model and interpret these phenomena in terms of recombination current modulation, identifying the distinct contributions from ion current and ionic charge accumulations. These contributions to the recombination current are associated with capacitive and inductive effects, respectively, and we corroborate the numerical simulations with electrochemical impedance spectroscopy measurements. These show the role of the recombination currents of photogenerated carriers in producing both capacitive and inductive effects as the illumination is varied. Moreover, we provide a bridging point between the two classes of models and suggest a framework of investigation of defect states based on the observed inductive behavior, which would further aid the mitigation of the degradation effects.
Open Access
10. Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment
Authors: Besleaga, C; Nan, B; Popa, AC; Balescu, LM; Nedelcu, L; Neto, AS; Pasuk, I; Leonat, L; Popescu-Pelin, G; Ferreira, JMF; Stan, GE

Published: SEP 2022, JOURNAL OF FUNCTIONAL BIOMATERIALS, 13, 123, DOI: 10.3390/jfb13030123

Bi-phasic calcium phosphates (BCPs) are considered prominent candidate materials for the fabrication of bone graft substitutes. Currently, supplemental cation-doping is suggested as a powerful path to boost biofunctionality, however, there is still a lack of knowledge on the structural role of such substituents in BCPs, which in turn, could influence the intensity and extent of the biological effects. In this work, pure and Mg- and Sr-doped BCP scaffolds were fabricated by robocasting from hydrothermally synthesized powders, and then preliminarily tested in vitro and thoroughly investigated physically and chemically. Collectively, the osteoblast cell culture assays indicated that all types of BCP scaffolds (pure, Sr- or Sr-Mg-doped) delivered in vitro performances similar to the biological control, with emphasis on the Sr-Mg-doped ones. An important result was that double Mg-Sr doping obtained the ceramic with the highest beta-tricalcium phosphate (beta-TCP)/hydroxyapatite mass concentration ratio of similar to 1.8. Remarkably, Mg and Sr were found to be predominantly incorporated in the beta-TCP lattice. These findings could be important for the future development of BCP-based bone graft substitutes since the higher dissolution rate of beta-TCP enables an easier release of the therapeutic ions. This may pave the road toward medical devices with more predictable in vivo performance.
11. The Behavior of Gold Metallized AlN/Si- and AlN/Glass-Based SAW Structures as Temperature Sensors
Authors: Nicoloiu, A; Stan, GE; Nastase, C; Boldeiu, G; Besleaga, C; Dinescu, A; Müller, A

Published: MAY 2021, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, 68, DOI: 10.1109/TUFFC.2020.3037789

Thin AlN piezoelectric layers have been deposited on high resistivity Si and glass substrates by reactive RF magnetron sputtering, in order to manufacture one-port gigahertz operating surface acoustic wave (SAW)-type resonators to be used as temperature sensors. The growth morphology surface topography, crystallographic structure, and crystalline quality of the AlN layers have been analyzed. Advanced nanolithographic techniques have been used to manufacture structures having interdigitated transducers with fingers and finger interdigit spacing width in the range of 250-170 nm. High resonance frequency ensures the increase of the sensitivity, but also of its normalized value, the temperature coefficient of frequency (TCF). The resonance frequency shift versus temperature has been measured in the -267 degrees C-+150 degrees C temperature range, using a cryostat setup adapted for on wafer microwave measurements up to 50 GHz. The sensitivity and the TCF were determined in the 25 degrees C-150 degrees C temperature range.
Open Access
12. Bistability of the BiOi complex and its implications on evaluating the "acceptor removal"process in p-type silicon
Authors: Besleaga, C; Kuncser, A; Nitescu, A; Kramberger, G; Moll, M; Pintilie, I

Published: NOV 21 2021, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1017, 165809, DOI: 10.1016/j.nima.2021.165809

The dependencies of the BiOi defect concentration on doping, irradiation fluence and particle type in p-type silicon diodes have been investigated. We evidenced that large data scattering occurs for fluences above 10(12) 1 MeV neutrons/cm(2), becoming significant larger for higher fluences. We show that the BiOi defect is metastable, with two configurations A and B, of which only A is detected by Deep Level Transient Spectroscopy and Thermally Stimulated Currents techniques. The defect' electrical activity is influenced by the inherent variations in ambient and procedural experimental conditions, resulting not only in a large scattering of the results coming from the same type of measurement but making correlation between different types of experiments difficult. It is evidenced that the variations in [BiOiA] are triggered by subjecting the samples to an excess of carriers, by either heating or an inherent short exposure to ambient light when manipulating the samples prior to experiments. For the samples investigated in this work both, the [BiOiA] as determined from electrical spectroscopic measurements and the full depletion voltage as measured from Current-Voltage characteristics reach a steady state in similar to 7h. Any electrical measurement performed before will give a different result. The bi-stable behavior of the BiOi defect fully accounts for these variations.
13. Enhancing stability of hybrid perovskite solar cells by imidazolium incorporation
Authors: Tomulescu, AG; Leonat, LN; Neatu, F; Stancu, V; Toma, V; Derbali, S; Neatu, S; Rostas, AM; Besleaga, C; Patru, R; Pintilie, I; Florea, M

Published: AUG 1 2021, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 227, 111096, DOI: 10.1016/j.solmat.2021.111096

Hybrid perovskites based solar cells have demonstrated high conversion efficiency but poor long-term stability. This study reports on the results obtained after doping the CH3NH3PbI2.6Cl0.4 mixed halide perovskite with imidazolium (C3N2H5+, denoted IM) on the "A site" position of a perovskite, to improve photovoltaic performances and stability of hybrid perovskite solar cells. The perovskite films were investigated exhaustively by different characterization techniques: X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy, UV-Vis, X-ray Photoelectron Electron Paramagnetic Resonance spectroscopies, Impedance Spectroscopy and Incident Photon-to-Electron Conversion Efficiency. The photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The amount of IM inserted in the perovskite play a key role on the film properties. The calculated new tolerance factors according to the "globularity factor" are experimentally proved and thus at doping concentrations greater than 20% for CH3NH3PbI2.6Cl0.4 perovskite the 3D structure is no longer obtained. However, below this value, the IM substituted perovskite film possesses an improved film quality and crystallinity as compared to the pristine film. Substituting MA+ with IM+ provides a favorable way to reduce recombination processes and shows great potential to achieve high stability, and an improved charge generation, resulting in increased PCE values. We find that the optimal percentage of imidazolium incorporation to achieve better stability of solar cells is 6%.
Open Access
14. The Beneficial Mechanical and Biological Outcomes of Thin Copper-Gallium Doped Silica-Rich Bio-Active Glass Implant-Type Coatings
Authors: Stan, GE; Tite, T; Popa, AC; Chirica, IM; Negrila, CC; Besleaga, C; Zgura, I; Sergentu, AC; Popescu-Pelin, G; Cristea, D; Ionescu, LE; Necsulescu, M; Fernandes, HR; Ferreira, JMF

Published: NOV 2020, COATINGS, 10, 1119, DOI: 10.3390/coatings10111119

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs(R)BG alkali-free SBG system (mol%: SiO2-38.49, CaO-36.07, P2O5-5.61, MgO-19.24, CaF2-0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (similar to 600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (R-RMS < 1 nm) and hydrophilic (water contact angle of similar to 65 degrees). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs(R)BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of similar to 53 MPa, Lc3 critical load value of similar to 4.9 N, hardness of similar to 6.1 GPa and an elastic modulus of similar to 127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays.
15. Influence of doping the inorganic cation with Eu or Sb on the properties of perovskite films
Authors: Stancu, V; Leonat, LN; Tomulescu, AG; Derbali, S; Pintilie, L; Besleaga, C; Galca, AC; Neatu, F; Neatu, T; Florea, M; Pintilie, I

Published: JUL 2020, PHYSICA SCRIPTA, 95, 075707, DOI: 10.1088/1402-4896/ab90be

This study reports on the results obtained after doping the [CH3NH3](0.94)[C3N2H5](0.06)PbI2.6Cl0.4 mixt halide perovskite with europium or antimony (Eu3+/Sb3+) at the 'B site'. This way two new complex compounds were obtained, [CH3NH3](0.94)[C3N2H5](0.06)Pb1-yByI2.6Cl0.4 (B = Eu or Sb and y = 0-0.05) as perovskite precursor solutions and deposited as thin films. The properties of the perovskite films were investigated by various characterization techniques: x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. We find that doping the mixt halide perovskite with very small quantities of Sb improves the quality of the perovskite films and further improves the stability of perovskite solar cells.
16. UAV identification system based on memristor physical unclonable functions
Authors: Ionescu, O; Besleaga, C; Dumitru, V; Pricop, E

Published: 2020, PROCEEDINGS OF THE 2020 12TH INTERNATIONAL CONFERENCE ON ELECTRONICS, COMPUTERS AND ARTIFICIAL INTELLIGENCE (ECAI-2020), DOI: 10.1109/ecai50035.2020.9223154

The latest decades presented a large development of various size and types of Unmanned Aerial Vehicles (UAVs). Nowadays, there are over 200 million UAVs used in various applications and there it is a large effort to adopt national and international regulation for using them. There it is a real need for the development of a reliable system for UAVs identity verification that can be implemented and used at global level. To this moment the software-based methods such as MAC address, IDs memorized on devices are prone to a large number of cyber-security vulnerabilities and attacks. This paper presents an innovative hardware-based identification solution which could be adapted to UAVs in a non-intrusive manner. The proposed solution is based on physical unclonable functions (PUF), which are implemented by using memristors. The proposed solution is very low cost and high performance. By using memristors, it is possible to generate a very large number of unclonable IDs, using only a few electrical components. This solution could be incorporated in any UAVs systems without major modifications and not affecting their flight parameters.
Open Access
17. Analog IGZO Memristor With Extended Capabilities
Authors: Dumitru, V; Besleaga, C; Ionescu, ON

Published: 2020, IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY, 8, DOI: 10.1109/JEDS.2020.3006000

In this paper an IGZO memristor with multiple states and analog tuning extended capability is reported. The device has a planar structure and is fabricated by magnetron sputtering on glass substrate. The device resistance could be gradually increased and decreased within the range of one order of magnitude. Larger resistance changes are also possible but they are mostly irreversible. The obtained memristor looks promising to be used as electronic synapse in hardware implemented artificial neural networks or for applications in analog computing and cryptography.
18. Ferroelectric Field Effect Transistors Based on PZT and IGZO
Authors: Besleaga, C; Radu, R; Balescu, LM; Stancu, V; Costas, A; Dumitru, V; Stan, G; Pintilie, L

Published: 2019, IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY, 7, 275, DOI: 10.1109/JEDS.2019.2895367

Ferroelectric field effect transistors (FeFETs) based on lead zirconate titanate (PZT) ferroelectric material and amorphous-indium-gallium-zinc oxide (a-IGZO) were developed and characterized. The PZT material was processed by a sol-gel method and then used as ferroelectric gate. The a-IGZO thin films, having the role of channel semiconductor, were deposited by radio-frequency magnetron sputtering, at a temperature of similar to 50 degrees C. Characteristics of a typical field effect transistor with SiO2 gate insulator, grown on highly doped silicon, and of the PZT-based FeFET were compared. It was proven that the FeFETs had promising performances in terms of I-on/I-off ratio (i.e., 10(6)) and IDS retention behavior.
19. The hysteresis-free behavior of perovskite solar cells from the perspective of the measurement conditions
Authors: Nemnes, GA; Besleaga, C; Tomulescu, AG; Leonat, LN; Stancu, V; Florea, M; Manolescu, A; Pintilie, I

Published: MAY 14 2019, JOURNAL OF MATERIALS CHEMISTRY C, 7, 5274, DOI: 10.1039/c8tc05999c

We investigate how far the hysteresis-free behavior of perovskite solar cells can be reproduced using particular pre-conditioning and measurement conditions. As there are currently more and more reports of perovskite solar cells without J-V hysteresis it is crucial to distinguish between genuine performance improvements and measurement artifacts. We focus on two of the parameters that influence the dynamic J-V scans, namely the bias scan rate and the bias poling voltage, and point out measurement conditions for achieving a hysteresis-free behavior. In this context we discuss the suitability of defining a hysteresis index (HI) for the characterization of dynamic J-V scans. Using HI, aging effects are also investigated, establishing a potential connection between the sample degradation and the variation of the maximal hysteresis on one hand, and the relaxation time scale of the slow process on the other hand. Pre-poling induced recombination effects are identified. In addition, our analysis based on sample pre-biasing reveals potential indications regarding two types of slow processes, with two different relaxation time scales, which provides further insight regarding ionic migration.
20. New bio-active, antimicrobial and adherent coatings of nanostructured carbon double-reinforced with silver and silicon by Matrix-Assisted Pulsed Laser Evaporation for medical applications
Authors: Duta, L; Ristoscu, C; Stan, GE; Husanu, MA; Besleaga, C; Chifiriuc, MC; Lazar, V; Bleotu, C; Miculescu, F; Mihailescu, N; Axente, E; Badiceanu, M; Bociaga, D; Mihailescu, IN

Published: MAY 31 2018, APPLIED SURFACE SCIENCE, 441, 883, DOI: 10.1016/j.apsusc.2018.02.047

We report on Matrix-Assisted Pulsed Laser Evaporation (MAPLE) deposition of Carbon thin films, simple or reinforced with intended concentrations of Ag and Si. A KrF* (lambda = 248 nm, tau(FWHM) < 25 ns, v = 10 Hz) excimer laser was used for irradiation. The effect of a post-deposition thermal treatment in vacuum was studied. Besides detailed morphological, compositional, structural and pull-out adherence characterizations, the potential of the carbonaceous films for medical applications was investigated in vitro by anti-biofilm and cytocompatibility assays. The microscopic images evidenced no delaminations. Micro-Raman spectroscopy revealed a graphitization tendency depending on preparation conditions, thermal treatment and reinforcing agents' presence. Adherence values improved considerably after thermal treatment. In vitro biological evaluation showed that the films containing similar to 1.85 at.% Ag were non-cytotoxic for MG63 cells, while eliciting a limited antimicrobial activity. The increase of Ag content to 3.6 at.% results in a significant enhancement of antimicrobial activity, whilst maintaining the cytotoxic action and adherence characteristics at acceptable levels. We propose a new class of metamaterials based on C reinforced with Ag and Si obtained by MAPLE for medical applications, i.e. the prevention and treatment of various infections associated with biofilms developed on implants and other medical equipments. (C) 2018 Elsevier B.V. All rights reserved.
21. The Influence of the Relaxation Time on the Dynamic Hysteresis in Perovskite Solar Cells
Authors: Palici, A; Nemnes, GA; Besleaga, C; Pintilie, L; Anghel, DV; Pintilie, I; Manolescu, A

Published: 2018, MATHEMATICAL MODELING AND COMPUTATIONAL PHYSICS 2017 (MMCP 2017), 173, DOI: 10.1051/epjconf/201817303017

We investigate the dynamic behavior of perovskite solar cells by focusing on the relaxation time tau, which corresponds to the slow de-polarization process from an initial bias pre-poled state. The dynamic electrical model (DEM) is employed for simulating the J-V characteristics for different bias scan rates and pre-poling conditions. Depending on the sign of the initial polarization normal or inverted hysteresis may be induced. For fixed pre-poling conditions, the relaxation time, in relation to the bias scan rate, governs the magnitude of the dynamic hysteresis. In the limit of large tau the hysteretic effects are vanishing for the typical range of bias scan rates considered, while for very small tau the hysteresis is significant only when it is comparable with the measurement time interval.
22. How measurement protocols influence the dynamic J-V characteristics of perovskite solar cells: Theory and experiment
Authors: Nemnes, GA; Besleaga, C; Tomulescu, AG; Palici, A; Pintilie, L; Manolescu, A; Pintilie, I

Published: OCT 2018, SOLAR ENERGY, 173, 983, DOI: 10.1016/j.solener.2018.08.033

The dynamic effects observed in the J-V measurements represent one important hallmark in the behavior of the perovskite solar cells. Proper measurement protocols (MPs) should be employed for the experimental data reproducibility, in particular for a reliable evaluation of the power conversion efficiency (PCE), as well as for a meaningful characterization of the type and magnitude of the hysteresis. We discuss here several MPs by comparing the experimental J-V characteristics with simulated ones using the dynamic electrical model (DEM). Pre-poling conditions and bias scan rate can have a dramatic influence not only on the apparent solar cell performance, but also on the hysteretic phenomena. Under certain measurement conditions, a hysteresis-free behavior with relatively high PCEs may be observed, although the J-V characteristics may be far away from the stationary case. Furthermore, forward-reverse and reverse-forward bias scans show qualitatively different behaviors regarding the type of the hysteresis, normal and inverted, depending on the bias pre-poling. We emphasize here that correlated double-scans, forward-reverse or reverse-forward, where the second scan is conducted in the opposite sweep direction and begins immediately after the first scan is complete, are essential for a correct assessment of the dynamic hysteresis. In this context, we define a hysteresis index which consistently assigns the hysteresis type and magnitude. Our DEM simulations, supported by experimental data, provide further guidance for an efficient and accurate determination of the stationary J-V characteristics, showing that the type and magnitude of the dynamic hysteresis may be affected by unintentional pre-conditioning in typical experiments.
23. Enhanced near-infrared response of a silicon solar cell by using an up-conversion phosphor film of Yb/Er - co-doped CeO2
Authors: Grigoroscuta, M; Secu, M; Trupina, L; Enculescu, M; Besleaga, C; Pintilie, I; Badica, P

Published: SEP 1 2018, SOLAR ENERGY, 171, 46, DOI: 10.1016/j.solener.2018.06.057

Co-doped CeO2 thin films were grown from a bulk target with starting composition Ce0.95Yb0.04Er0.01O2 by pulsed laser deposition (PLD) on a p(+)-n-n(+) single crystal silicon diode. The PLD laser fluence was varied between 1.7 J/cm(2) and 3.7 J/cm(2). The device with the film grown for a laser fluence of 2.3 J/cm(2) delivers the highest performance taking advantage of the up conversion (UC) effect provided by this film. Namely, the increase in the relative power conversion efficiency of the device is 12.1% and 39.2% for illumination under 1 and 2.1 sun, respectively, and its relative external quantum efficiency is 8.2% when illuminated with 980 nm light. The film grown for the optimum 2.3 J/cm(2) fluence shows good target-film composition transfer and a granular morphology with a low roughness. The UC mechanism consists of efficient energy transfer between spatially separated Yb3+ and Er3+ ions, i.e. the absorption of infrared light photons by the Yb3+ ions (F-2(7/2) -> F-2(5/2) transition) is followed by a two-step energy transfer process to neighboring Er3+ ions and by their characteristic luminescent emissions ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and (F-4(9/2) -> I-4(15/2)).
24. Normal and Inverted Hysteresis in Perovskite Solar Cells
Authors: Nemnes, GA; Besleaga, C; Stancu, V; Dogaru, DE; Leonat, LN; Pintilie, L; Torfason, K; Ilkov, M; Manolescu, A; Pintilie, I

Published: JUN 1 2017, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 11214, DOI: 10.1021/acs.jpcc.7b04248

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.
25. Dynamic electrical behavior of halide perovskite based solar cells
Authors: Nemnes, GA; Besleaga, C; Tomulescu, AG; Pintilie, I; Pintilie, L; Torfason, K; Manolescu, A

Published: JAN 2017, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 159, 203, DOI: 10.1016/j.solmat.2016.09.012

A dynamic electrical model is introduced to investigate the hysteretic effects in the J-V characteristics of perovskite based solar cells. By making a simple ansatz for the polarization relaxation, our model is able to reproduce qualitatively and quantitatively detailed features of measured J-V characteristics. Pre-poling effects are discussed, pointing out the differences between initially over- and under-polarized samples. In particular, the presence of the current overshoot observed in the reverse characteristics is correlated with the solar cell pre-conditioning. Furthermore, the dynamic hysteresis is analyzed with respect to changing the bias scan rate, the obtained results being consistent with experimentally reported data: the hysteresis amplitude is maximum at intermediate scan rates, while at very slow and very fast ones it becomes negligible. The effects induced by different relaxation time scales are assessed. The proposed dynamic electrical model offers a comprehensive view of the solar cell operation, being a practical tool for future calibration of tentative microscopic descriptions. (C) 2016 Elsevier B.V. All rights reserved.
26. Characterization of PLD grown WO3 thin films for gas sensing
Authors: Boyadjiev, SI; Georgieva, V; Stefan, N; Stan, GE; Mihailescu, N; Visan, A; Mihailescu, IN; Besleaga, C; Szilagyi, IM

Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 223, DOI: 10.1016/j.apsusc.2017.03.212

Tungsten trioxide (WO3) thin films were grown by pulsed laser deposition (PLD) with the aim to be applied in gas sensors. The films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and profilometry. To study the gas sensing behavior of these WO3 films, they were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was applied to analyze their gas sensitivity. Synthesis of tetragonal-WO3 films starting from a target with predominantly monoclinic WO3 phase was observed. The films deposited at 300 degrees C presented a surface topology favorable for the sorption properties, consisting of a film matrix with protruding craters/cavities. QCM prototype sensors with such films were tested for NO2 sensing. The PLD grown WO3 thin films show good sensitivity and fast reaction at room temperature, even in as-deposited state. With the presented technology, the manufacturing of QCM gas sensors is simple, fast and cost-effective, and it is also suitable for energy-effective portable equipment for on-line monitoring of environmental changes. (C) 2017 Elsevier B.V. All rights reserved.
27. Characterization of MAPLE deposited WO3 thin films for electrochromic applications
Authors: Boyadjiev, SI; Stefan, N; Szilagyi, IM; Mihailescu, N; Visan, A; Mihailescu, IN; Stan, GE; Besleaga, C; Iliev, MT; Gesheva, KA

Published: 2017, INERA WORKSHOP 2016: MEMBRANE AND LIQUID CRYSTAL NANOSTRUCTURES (MELINA 2016), 780, DOI: 10.1088/1742-6596/780/1/012013

Tungsten trioxide (WO3) is a widely studied material for electrochromic applications. The structure, morphology and optical properties of WO3 thin films, grown by matrix assisted pulsed laser evaporation (MAPLE) from monoclinic WO3 nano-sized particles, were investigated for their possible application as electrochromic layers. A KrF* excimer (lambda = 248 nm, .zeta(FWHM)=25 ns) laser source was used in all experiments. The MAPLE deposited WO3 thin films were studied by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry measurements were also performed, and the coloring and bleaching were observed. The morpho-structural investigations disclosed the synthesis of single-phase monoclinic WO3 films consisting of crystalline nano-grains embedded in an amorphous matrix. All thin films showed good electrochromic properties, thus validating application of the MAPLE deposition technique for the further development of electrochromic devices.
28. Comparative physical, chemical and biological assessment of simple and titanium-doped ovine dentine-derived hydroxyapatite coatings fabricated by pulsed laser deposition
Authors: Duta, L; Mihailescu, N; Popescu, AC; Luculescu, CR; Mihailescu, IN; Cetin, G; Gunduz, O; Oktar, FN; Popa, AC; Kuncser, A; Besleaga, C; Stan, GE

Published: AUG 15 2017, APPLIED SURFACE SCIENCE, 413, 139, DOI: 10.1016/j.apsusc.2017.04.025

We report on the synthesis by Pulsed Laser Deposition of simple and Ti doped hydroxyapatite thin films of biological (ovine dentine) origin. Detailed physical, chemical, mechanical and biological investigations were performed. Morphological examination of films showed a surface composed of spheroidal particulates, of micronic size. Compositional analyses pointed to the presence of typical natural doping elements of bone, along with a slight non-stoichiometry of the deposited films. Structural investigations proved the monophasic hydroxyapatite nature of both simple and Ti doped films. Ti doping of biological hydroxyapatite induced an overall downgrade of the films crystallinity together with an increase of the films roughness. It is to be emphasized that bonding strength values measured at film. Ti substrate interface were superior to the minimum value imposed by International Standards regulating the load-bearing implant coatings. In vitro tests on Ti doped structures, compared to simple ones, revealed excellent biocompatibility in human mesenchymal stem cell cultures, a higher proliferation rate and a good cytocompatibility. The obtained results aim to elucidate the overall positive role of Ti doping on the hydroxyapatite films performance, and demonstrate the possibility to use this novel type of coatings as feasible materials for future implantology applications. (C) 2017 Elsevier B.V. All rights reserved.
29. Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure
Authors: Besleaga, C; Dumitru, V; Trinca, LM; Popa, AC; Negrila, CC; Kolodziejczyk, L; Luculescu, CR; Ionescu, GC; Ripeanu, RG; Vladescu, A; Stan, GE

Published: NOV 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7110394

Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c-axis texturing, deposited at a low temperature (similar to 50 degrees C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials.
30. TEMPERATURE INFLUENCE ON THE CAPACITANCE-VOLTAGE HYSTERESIS OF TRANSPARENT a-IGZO/PZT/FTO MFS-HETEROSTRUCTURE
Authors: Trinca, LM; Besleaga, C; Stancu, V; Radu, R; Iuga, A; Boni, AG; Galca, AC; Pintilie, L

Published: 2017, ROMANIAN REPORTS IN PHYSICS, 69, DOI:

Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.
31. Submicrometer Hollow Bioglass Cones Deposited by Radio Frequency Magnetron Sputtering: Formation Mechanism, Properties, and Prospective Biomedical Applications
Authors: Popa, AC; Stan, GE; Besleaga, C; Ion, L; Maraloiu, VA; Tulyaganov, DU; Ferreira, JMF

Published: FEB 24 2016, ACS APPLIED MATERIALS & INTERFACES, 8, 4367, DOI: 10.1021/acsami.6b00606

This work reports on the unprecedented magnetron sputtering deposition of submicrometric hollow cones of bioactive glass at low temperature in the absence of any template or catalyst. The influence of sputtering conditions on the formation and development of bioglass cones was studied. It was shown that larger populations of well-developed cones could be achieved by increasing the argon sputtering pressure. A mechanism describing the growth of bioglass hollow cones is presented, offering the links for process control and reproducibility of the cone features. The composition, structure, and morphology of the as-synthesized hollow cones were investigated by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), grazing incidence geometry X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)-selected area electron diffraction (SAED). The in vitro biological performance, assessed by degradation tests (ISO 10993-14) and cytocompatibility assays (ISO 10993-5) in endothelial cell cultures, was excellent. This allied with resorbability and the unique morphological features make the submicrometer hollow cones interesting candidate material devices for focal transitory permeabilization of the blood brain barrier in the treatment of carcinoma and neurodegenerative disorders.
32. Fabrication of periodical surface structures by picosecond laser irradiation of carbon thin films: transformation of amorphous carbon in nanographite
Authors: Popescu, C; Dorcioman, G; Bita, B; Besleaga, C; Zgura, I; Himcinschi, C; Popescu, AC

Published: DEC 30 2016, APPLIED SURFACE SCIENCE, 390, 243, DOI: 10.1016/j.apsusc.2016.08.029

Thin films of carbon were synthesized by ns pulsed laser deposition in vacuum on silicon substrates, starting from graphite targets. Further on, the films were irradiated with a picosecond laser source emitting in visible at 532 nm. After tuning of laser parameters, we obtained a film surface covered by laser induced periodical surface structures (LIPSS). They were investigated by optical, scanning electron and atomic force microscopy. It was observed that changing the irradiation angle influences the LIPSS covered area. At high magnification it was revealed that the LIPSS pattern was quite complex, being composed of other small LIPSS islands, interconnected by bridges of nanoparticles. Raman spectra for the non-irradiated carbon films were typical for a-C type of diamond-like carbon, while the LIPSS spectra were characteristic to nano-graphite. The pristine carbon film was hydrophilic, while the LIPSS covered film surface was hydrophobic. (C) 2016 Elsevier B.V. All rights reserved.
33. Fabrication of antimicrobial silver-doped carbon structures by combinatorial pulsed laser deposition
Authors: Mihailescu, IN; Bociaga, D; Socol, G; Stan, GE; Chifiriuc, MC; Bleotu, C; Husanu, MA; Popescu-Pelin, G; Duta, L; Luculescu, CR; Negut, I; Hapenciuc, C; Besleaga, C; Zgura, I; Miculescu, F

Published: DEC 30 2016, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 515, 606, DOI: 10.1016/j.ijpharm.2016.10.041

We report on the selection by combinatorial pulsed laser deposition of Silver-doped Carbon structures with reliable physical-chemical characteristics and high efficiency against microbial biofilms. The investigation of the films was performed by scanning electron microscopy, high resolution atomic force microscopy, energy dispersive X-Ray Spectroscopy, X-ray diffraction, Raman spectroscopy, bonding strength "pull-out" tests, and surface energy measurements. In vitro biological assays were carried out using a large spectrum of bacterial and fungal strains, i.e., Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Enterococcus faecalis and Candida albicans. The biocompatibility of the films obtained was evaluated on MG63 mammalian cell cultures. The optimal combination with reasonable physical-chemical properties, efficient protection against microbial colonization and beneficial effects on human cells was found for Silver-doped Carbon films containing 2 to 7 at.% silver. These mixtures can be used to fabricate safe and efficient coatings of metallic implants, with the goal to decrease the risk of implant associated biofilm infections which are difficult to treat and often responsible for implant failure. (C) 2016 Elsevier B.V. All rights reserved.
34. Combinatorial MAPLE deposition of antimicrobial orthopedic maps fabricated from chitosan and biomimetic apatite powders
Authors: Visan, A; Stan, GE; Ristoscu, C; Popescu-Pelin, G; Sopronyi, M; Besleaga, C; Luculescu, C; Chifiriuc, MC; Hussien, MD; Marsan, O; Kergourlay, E; Grossin, D; Brouillet, F; Mihailescu, IN

Published: SEP 10 2016, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 511, 515, DOI: 10.1016/j.ijpharm.2016.07.015

Chitosan/biomimetic apatite thin films were grown in mild conditions of temperature and pressure by Combinatorial Matrix-Assisted Pulsed Laser Evaporation on Ti, Si or glass substrates. Compositional gradients were obtained by simultaneous laser vaporization of the two distinct material targets. A KrF* excimer (lambda = 248 nm, tau(FWHM) = 25 ns) laser source was used in all experiments. The nature and surface composition of deposited materials and the spatial distribution of constituents were studied by SEM, EDS, AFM, GIXRD, FTIR, micro-Raman, and XPS. The antimicrobial efficiency of the chitosan/biomimetic apatite layers against Staphylococcus aureus and Escherichia coli strains was interrogated by viable cell count assay. The obtained thin films were XRD amorphous and exhibited a morphology characteristic to the laser deposited structures composed of nanometric round shaped grains. The surface roughness has progressively increased with chitosan concentration. FTIR, EDS and XPS analyses indicated that the composition of the BmAp-CHT C-MAPLE composite films gradually modified from pure apatite to chitosan. The bioevaluation tests indicated that S. aureus biofilm is more susceptible to the action of chitosanrich areas of the films, whilst the E. coli biofilm proved more sensible to areas containing less chitosan. The best compromise should therefore go, in our opinion, to zones with intermediate-to-high chitosan concentration which can assure a large spectrum of antimicrobial protection concomitantly with a significant enhancement of osseointegration, favored by the presence of biomimetic hydroxyapatite. (C) 2016 Elsevier B.V. All rights reserved.
35. Iodine Migration and Degradation of Perovskite Solar Cells Enhanced by Metallic Electrodes
Authors: Besleaga, C; Abramiuc, LE; Stancu, V; Tomulescu, AG; Sima, M; Trinca, L; Plugaru, N; Pintilie, L; Nemnes, GA; Iliescu, M; Svavarsson, HG; Manolescu, A; Pintilie, I

Published: DEC 15 2016, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 7, 5175, DOI: 10.1021/acs.jpclett.6b02375

We monitored the evolution in time of pinhole-free structures based on FTO/TiO2/CH3NH3PbI2.6Cl0.4 layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 degrees C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 degrees C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I- from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I- negative space charge accumulated at the perovskite-OMeTAD interface.
36. Transparent field-effect transistors based on AlN-gate dielectric and IGZO-channel semiconductor
Authors: Besleaga, C; Stan, GE; Pintilie, I; Barquinha, P; Fortunato, E; Martins, R

Published: AUG 30 2016, APPLIED SURFACE SCIENCE, 379, 276, DOI: 10.1016/j.apsusc.2016.04.083

The degradation of thin-film transistors (TFTs) caused by the self-heating effect constitutes a problem to be solved for the next generation of displays. Aluminum nitride (AlN) is a viable alternative for gate dielectric of TFTs due to its good thermal conductivity, matching coefficient of thermal expansion to indium-gallium-zinc-oxide, and excellent stability at high temperatures. Here, AlN thin films of different thicknesses were fabricated by a low temperature reactive radio-frequency magnetron sputtering process, using a low cost, metallic Al target. Their electrical properties have been thoroughly assessed. Furthermore, the 200 nm and 500 nm thick AlN layers have been integrated as gate-dielectric in transparent TFTs with indium-gallium-zinc-oxide as channel semiconductor. Our study emphasizes the potential of AlN thin films for transparent electronics, whilst the functionality of the fabricated field-effect transistors is explored and discussed. (C) 2016 Elsevier B.V. All rights reserved.
37. AZO THIN FILMS SYNTHESIZED BY RF-MAGNETRON SPUTTERING: THE ROLE OF DEPOSITION POWER
Authors: Besleaga, C; Ion, L; Antohe, S

Published: 2014, ROMANIAN REPORTS IN PHYSICS, 66, 1001, DOI:

Transparent c-axis textured aluminum doped zinc oxide (AZO) films were deposited at room temperature onto glass substrates by radio-frequency magnetron sputtering. The effect of sputtering power on the properties of the AZO sputtered thin films was investigated. Our results indicated that the sputtering power has a great influence on the crystalline quality and electrical parameters of AZO films, thus being a useful tool for tuning their functional properties.
38. Physical properties of AlxIn1-xN thin film alloys sputtered at low temperature
Authors: Besleaga, C; Galca, AC; Miclea, CF; Mercioniu, I; Enculescu, M; Stan, GE; Mateescu, AO; Dumitru, V; Costea, S

Published: OCT 21 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4898565

In this paper, we report on the structural, optical, and electrical properties of a wide compositional range of AlxIn1-xN thin layers deposited on glass and polyethylene terephthalate substrates. AlxIn1-xN layers of controlled composition were obtained by a simple reactive magnetron co-sputtering protocol, using a single aluminium target with indium insets, by varying the Al/In target surface area ratio, and the composition of the deposition atmosphere. The relevant physical properties were investigated and discussed. It is shown that the texture of the thin films is dependent on the cation ratio, while the bowing parameters of lattice constants and band gap values are larger than those of epitaxial layers. (C) 2014 AIP Publishing LLC.
39. InN Based Water Condensation Sensors on Glass and Flexible Plastic Substrates
Authors: Dumitru, V; Costea, S; Brezeanu, M; Stan, GE; Besleaga, C; Galca, AC; Ionescu, G; Ionescu, O

Published: DEC 2013, SENSORS, 13, 16949, DOI: 10.3390/s131216940

40. Double layer structure of ZnO thin films deposited by RF-magnetron sputtering on glass substrate
Authors: Besleaga, C; Stan, GE; Galca, AC; Ion, L; Antohe, S

Published: SEP 1 2012, APPLIED SURFACE SCIENCE, 258, 8824, DOI: 10.1016/j.apsusc.2012.05.097

Transparent ZnO films are synthesized by RF-magnetron sputtering (1.78 MHz) onto glass substrates, using a mild-pressed ZnO powder target. The depositions were carried at three inert argon pressures (0.25 Pa, 0.30 Pa, and 0.45 Pa) at two substrate temperatures (100 degrees C and 400 degrees C). The role of the sputtering conditions on ZnO thin films nanostructuring, optical properties and morphology is investigated by Xray diffraction (XRD), X-ray reflectometry (XRR) and Spectroscopic ellipsometry (SE). XRD investigations revealed that ZnO films show a (0 0 l) texture with nanosized crystallites. Right-angle asymmetry of the (0 0 2) diffraction peak is observed. The peak profile analysis using pseudo-Voigt functions unveils a double overlapped peak structure with different coherent zone size values. A double layer structure is evidenced by analyzing the XRR data. Samples prepared at 0.3 Pa at a temperature of 400 degrees C have a similar to 4 nm bottom layer consisting of highly depleted in oxygen ZnO1-x structure, continued by a 53 nm top layer of textured ZnO. Electrical measurements show that the temperature dependence of the conductivity is well described by the Mott variable range hopping (VRH) law. The samples obtained at 400 degrees C have a significantly lower resistivity. (C) 2012 Elsevier B. V. All rights reserved.
41. Transparent indium zinc oxide thin films used in photovoltaic cells based on polymer blends
Authors: Besleaga, C; Ion, L; Ghenescu, V; Socol, G; Radu, A; Arghir, I; Florica, C; Antohe, S

Published: SEP 1 2012, THIN SOLID FILMS, 520, 6806, DOI: 10.1016/j.tsf.2012.07.030

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.
42. High quality amorphous indium zinc oxide thin films synthesized by pulsed laser deposition
Authors: Socol, G; Craciun, D; Mihailescu, IN; Stefan, N; Besleaga, C; Ion, L; Antohe, S; Kim, KW; Norton, D; Pearton, SJ; Galca, AC; Craciun, V

Published: DEC 1 2011, THIN SOLID FILMS, 520, 1277, DOI: 10.1016/j.tsf.2011.04.196

Indium zinc oxide films were grown from targets with two different In atomic concentration [In/(In+Zn)] of 40% and 80% by the pulsed laser deposition technique on glass substrates from room temperature up to 100 degrees C. X-ray diffraction and reflectometry investigations showed that films were amorphous and dense. Thin films (thickness<100 nm) exhibited higher optical transmittance and resistivities than thick films (thickness>1000 nm), probably caused by a significant decrease of oxygen vacancies due to atmosphere exposure. Films deposited from the In rich target under an oxygen pressure of 1 Pa exhibited optical transmittance higher than 85%, resistivities around 5-7x10(-4) Omega cm and mobilities in the 47-54 cm(2)/V s range. (C) 2011 Elsevier B. V. All rights reserved.
43. The Influence of Magnetron Sputtering Conditions on the Physical Properties of (001) Oriented Nanostructured ZnO Thin Films
Authors: Simon, S; Besleaga, C; Stan, GE; Ion, L; Arghir, I; Antohe, S

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647074

Smooth, transparent and highly oriented nanostructured ZnO films were synthesized by RF-magnetron sputtering onto Si(100) substrates. A mild-pressed zinc oxide powder target was used for all depositions. The sputtering parameters were varied in order to obtain structures with good adherence and crystallinity. The depositions were carried out in inert argon atmosphere at four sputtering pressures (0.2 Pa, 0.25 Pa, 0.3 Pa and 0.45 Pa). ZnO films were deposited at 150 degrees C. The films were characterized from structural (XRD) and morphological (AFM) point of view. The influence of each sputtering parameter on the morphological and structural properties is discussed.
44. EFFECTS OF PROTON IRRADIATION ON THE SPECTRAL PERFORMANCE OF PHOTOVOLTAIC CELLS BASED ON CdS/CdTe THIN FILMS
Authors: Ion, L; Enculescu, I; Iftimie, S; Ghenescu, V; Tazlaoanu, C; Besleaga, C; Mitran, TL; Antohe, VA; Gugiu, MM; Antohe, S

Published: AUG 2010, CHALCOGENIDE LETTERS, 7, 530, DOI:

Due to their physical and chemical properties (such as suitable band gaps, large absorption coefficients and good chemical stability) CdTe thin films are interesting for electronic and optoelectronic devices, including particularly photovoltaic cells for space technology. For that specific application, it is of prime importance to study in this type of materials the influence of ionizing radiations on their physical (structural, electrical and optical) properties. In this paper, the photovoltaic cells based on CdS/CdTe thin films, produced by thermal vacuum sublimation, were irradiated with 3 MeV protons at room temperature. The effects of irradiation were studied by investigating the changes in the electrical and optical properties of the cells. It was found that proton irradiation in the above mentioned conditions results mainly in the introduction of defects at the CdS/CdTe interface. A discussion about the possible origin of those defects is given.
45. Pyramidal morphology of InN thin films deposited by reactive RF-magnetron sputtering
Authors: Zoita, NC; Besleaga, C; Braic, L; Mitran, T; Vlaicu, M

Published: DEC 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 797, DOI:

Indium nitride is an attractive semiconductor material for optoelectronic applications, high-speed electronics and solar cells. We report deposition of polycrystalline InN thin films with pyramidal morphology on different substrates by reactive RF magnetron sputtering method. The morphological characterization if the films are presented in corroboration with the deposition parameters and the observed crystallographic structure.
46. InN thin films deposited on flexible substrates by reactive RF-magnetron sputtering
Authors: Zoita, NC; Besleaga, C; Braic, L; Mitran, T; Grigorescu, C; Nedelcu, L

Published: NOV 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 720, DOI:

Indium nitride is an attractive semiconductor material for optoelectronic applications, high-speed electronics and solar cells. We report successful deposition of polycrystalline InN thin films onto kapton polyimide flexible substrates by reactive RF magnetron sputtering method. The optical, structural and morphological characterization data are presented.
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