Up-graded list of personnel (November 2015)

Scientific report year 2012 (in Romanian)-Download

Scientific report for year 2013 (in Romanian)-download

Scientific report for year 2014 (in Romanian)-download

Scientific report for year 2015 (in Romanian)-download

Sintetic report 2016 (in Romanian)-download

Important results:

The study of electrode-ferroelectric interface was performed by using different characterization tehniques, such as: X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM, piezoelectric force microscopy (PFM), macroscopic electrical measurements (I-V, C-V, hysteresis, etc.).

Metals such as Au, Cu and Pt were tested as electrodes on PZT (lead zirconate-titanate) and BTO (barium titanate) epitaxial filmsgrown by pulsed laser deposition (PLD). The bottom electrode was in all cases SRO (strontium ruthenate). The three metals were deposited by molecular beam epitaxy (MBE) on the surface of the ferroelectric film. The deposition, for each metal, was sequential starting with 2 atomic layers and ending to a thickness of 10 nm. After each deposited metal layer XPS measurements were performed in order to investigate the band bending at the interface. The results with Au were already published, while the results on Cu and Pt are under evaluation.

Example of the binding energy shifting for Au (published in Applied Surface Science).

HR-TEM images of the deposited layer (published in Applied Surface Science). The gold layer seems to be not continous and not very adherent. That can explain the larger potential barrier determined from I-V measurements at different temperatures, compared to Cu or Pt.

Several papers were published in journals with high impact factor, supporting the hypothesis that the properties of the electrode interfaces in ferroelectric capacitors are strongly influenced by the polarization charges. Especially in the case of the epitaxial films, in which case the polarization is actually controlling the interface properties (see for example the article "Polarization-Control of the Potential Barrier at the Electrode Interfaces in Epitaxial Ferroelectric Thin Films";By: Pintilie, Ioana; Teodorescu, Cristian Mihail; Ghica, Corneliu; et al.ACS APPLIED MATERIALS & INTERFACES  Volume: 6   Issue: 4   Pages: 2936-2946   Published: FEB 26 2014"). This fact is very well reflected by the following table:

The voltage dependence of capacitance and the frequency dependence of the complex impedance were measured for PZT and BTO films, grown on single crystal STO substrates with different orientations, and having different metals as top electrodes. The C-V measurements suggest the presence of Schottky type contacts at the electrode interfaces. These were used to extract information about the dielectric constant in the depleted region and about the concentration of the free carriers. The frequency dependence of the imaginary part of the complex impedance suggests a dominant capacitive reactance. Its frequency dependence was simulated with an equivalent circuit consisting of four elements: a contact resistance; a capacitance associated to the Schottky contacts; a parallel R-C connection describing the ferroelectric volume of the film. However, the values extracted for the elements of the equivalent circuit by fitting the equation (2”) with the experimental data of the imaginary part of the complex impedance do not fit very well the real part of the complex impedance especially at low frequencies. This may be due to the active traps in the low frequency range. Equations (2’) and (2”) show that for high frequencies the equivalent circuit can be reduced to a simple serial R-C circuit, as already reported for other devices.

The frequency dependence of the imaginary part of the complex impedance of a ferroelectric film deposited on STO substrates with different orientation: (a) BTO grown on STO(001); (b) PZT grown on STO(001); (c) BTO grown on STO(111); (d) PZT grown on STO(111).The inset shows the frequency dependence of the real part of the complex impedance for BTO on STO(001) (Published in Journal of Applied Physics 116, 044108 (2014))

Remarkably is that the behavior is about the same for different ferroelectric materials, grown on substrates with different orientations and having different top electrodes. The exception is Al, in which case the results strongly support the formation of the thin layer of aluminum oxide affecting the properties of the interface and the equivalent dielectric constant of the ferroelectric capacitor. There are also evidences that a thin Cu oxide layer may form in the case of top Cu electrode. However, except Al, the values extracted for the capacitance CS of the Schottky contact and for the apparent built-in potential Vbi’ does not differ significantly considering that the work function difference between Pt and Cu is about 1 eV. These results support the assumption that the equivalent circuit can be used for any epitaxial ferroelectric film and that the polarization control of electrode interfaces is a general phenomenon in the case of capacitor based on epitaxial ferroelectrics. The effect of spontaneous polarization on the properties of Schottky contacts was observed also in the case of polar semiconductor.

The behaviour of SRO layer deposited on STO substrate was investigated. The work has been intended to elucidate a particular microstructural aspect observed in the case of epitaxial perovskite multilayers used as artificial multiferroics. The focus was on explaining the origin of supplementary diffraction spots appearing in forbidden positions in the electron diffraction patterns from selected areas on cross-section multilayered PZT/CFO/PZT/SRO coatings deposited on STO(001) single crystal substrates. By SAED experiments and Fourier filtering of the HRTEM images, the faint diffraction spots noticed in the SAED patterns have been attributed to the SrRuO3 layer used as bottom electrode. By Geometrical Phase Analysis of the HRTEM micrographs we have shown the straightforward relation between the strain distribution inside the SRO layer and the formation of the structurally distorted nanometric domains in SRO. The distortion mechanism consists in a cooperative tilting of the RuO6 octahedra under the compressive strain revealed by GPA. We have shown that the forbidden diffraction spots observed in the SAED patterns originate from nanometric areas inside the SrRuO3 layer, where high values of a local compressive strain have been measured (-4 ÷-5 %). The high local strain leads to a local monoclinic distortion of the orthorhombic lattice of SRO, suppressing the screw axis along [010]SRO and enabling the appearance of diffraction spots in forbidden positions. The further confirmation on the origin of the forbidden spots comes from the simulated diffraction patterns obtained from a monoclinic distorted SRO lattice, where the 0k0SRO spots, k=2n+1, are observed, unlike the orthorhombic undistorted lattice. Although our work does not include an exact crystallographic model of a monoclinic distorted cell of SrRuO3, it provides a mechanism to explain the origin of the observed forbidden spots in the diffraction patterns of the SRO thin films, proving a direct correlation between the compressive strain and the monoclinic distortion in nanosized domains.

HRTEM image including the SRO layer and neighboring areas from the STO substrate and PZT overgrown layer. (b) Corresponding power spectrum. (c) and (d) Bragg-filtered images obtained with the selected reciprocal spots 1 and 2, respectively. Details in Journal of Applied Physics 116, 023516 (2014).

Important results were obtained also regarding the core-shell structures, either in spherical or in cylindrical geometry. Recently were synthetised complex heterostructures formed by Fe nanowires embedded in a matrix of PZT. This will aloow investigation of electrical/magnetic properties in 1D-like geometry, different from the classical case of multilayers.

By Raman measurements combined with Moessbauer spectroscopy it was found that Fe₂O₃ forms at the Fe-PZT interface during the PZT deposition by PLD (details in a paper published in Physica Status Solidi)

On CoFe₂O₄ (CFO)-PZT systems grown as multilayers was shown the presence of multiferroic properties (see the figure below)

Some measurements were also performed on core-shell structures based on BTO and a-Fe₂O₃. It was found that the structures show magnetic properties and good magnetoresistence. BaTiO3–ferrite multiphase composites were prepared starting from di-phase mixtures of -Fe2O3 and BaTiO3 powders. During the sintering step, the formation of small amounts of secondary phases with multifunctional character as BaFe12O19 or Ba12Ti28Fe15O84 was promoted. The resulting multiphase ceramic compounds show interesting dielectric, magnetic and small magnetocapacitance effect at low temperature. The coexistence of different magnetic phases with contrasting coercivities (hard/soft) was detected by the presence of ‘waspwaisted’M(H) hysteresis loops and first-order reversal curve analysis. The present approach demonstrates that active materials can be realised by controlling in situ
reactions at the interfaces in ferroelectric–magnetic oxide composites.

Photoelectron spectroscopy studies of (001) oriented PbTi0.8Zr0.2O3 (PZT) single crystal layers with
submicron resolution revealed areas with different Pb 5d binding energies, attributed to the different charge and polarization states of the film surface. Two novel effects are evidenced by using intense synchrotron radiation beam experiments: (i) the progressive increase of a low binding energy component for the Pb core levels (evidenced for both 5d and 4f, on two different measurement setups), which can be attributed to a partial decomposition of the PZT film at its surface and promoting the growth of metallic Pb during the photoemission process, with the eventuality of the progressive formation of areas with downwards ferroelectric polarization; (ii) for films annealed in oxygen under clean conditions (in an ultrahigh vacuum installation) a huge shift of the Pb 5d core levels (by 8–9 eV) towards higher binding energies is attributed to the formation of areas with depleted mobile charge carriers, whose surface density is insufficient to screen the depolarization field. This shift is attenuated progressively with time, as the sample is irradiated with high flux soft X-rays. The formation of these areas with strong internal electric field promotes these films as good candidates for photocatalysis and solar cells, since in the operation of these devices the ability to perform charge separation and to avoid electron–hole recombination is crucial.

It was found that the pyroelectric signal generated by an epitaxial Pb(Zr0.2Ti0.8)O3 film can be enhanced by continuous illumination with ultraviolet (UV) light. The measured signal increases more than 2
times at low modulation frequencies of the incident infrared (IR) radiation (10 Hz) and at
wavelengths where the short-circuit photocurrent presents the maximum value (280–300 nm).
The tentative explanation is that the changes in polarization induced by the temperature variation
under modulated IR illumination are generating a variable internal electric field, able to collect the
photogenerated carriers produced under continuous UV illumination leading to an additional signal
in phase with the pyroelectric one. This finding could be exploited for designing pyroelectric
detectors with enhanced characteristics by combining both UV and IR responses.

An important result obtained in 2015 was the discovery of a self-doping mechanism taking place in epitaxial PZT films during the growth phase. The self-doping is promoted by the necessity to compensate the depolarization field occuring in the film due to the fact that the polarization is oriented towards the growing surface. The results were published in Scientific Reports (a Nature Publishing Group journal).

XRD diffraction patterns and TEM images of the samples used for the study related to the self-doping phenomena. It is demonstrated the high epitaxial quality of the PZT films.

Results of the electrical measurements showing that the amplitude of the self-doping effect is reverse proportional with the thickness of the PZT films, leading to a concentration of free carrier that increases as the film thickness decreases.

Another important result was to obtain core-shell structures with conical geometry formed by ZnO nano-cones covered with barium titanate (see the figure above).

In the case of the ZnO/Zn1−xMnxO/BaTiO3nanostructure, Ramanscattering and XRD measurements showed the formation of aBaTiO3layer with structure that corresponds to ferroelectric tetragonal phase.

The presence of the principal peaks both of the ZnO/Zn1−xMnxOcore and BaTiO3shell, without significant shifts, in the Raman spectrum of the ZnO/Zn1−xMnxO/BaTiO3 nanostructure suggests lack of unwanted phases, resulted by interfusion or chemical reactions, at the interfaces.

ZnO nanowires were prepared by electrochemical methods.

SEM images of ZnO nanowires.

The ZnO nanoweires were then spread on the surface of a PZT film deposited on a Si substrate using the technique that it is schematically presented in the figures below.

SEM images of the ZnO nanowires spread on the surface of the PZT film and contacted with Ti/Au electrodes after using electron beam lithography.

6 PhD positions were occupied: 5 at the coordinating institution (NIMP) and 1 at the partner university (UAIC).

PhD students emploied at NIMP, the provisional title of the thesis and the PhD supervisor:

PhD student emploied at UAIC:

Leonetin Padurariu-will develop complex models for simulating the behavior of ferroelectric structures

Stoflea (married Abramiuc) Laura-started PhD in 2014 on ferroelectric surfaces/interfaces for catalysis and photo-catalysis

The post-doc position at NIMP was occupied in 2013 by:

Hrib Luminita-will prepare and characterize new oxide materials with ferromagnetic properties, such as double perovskites

2 young scientists started PhD studies in the last year: Tache Cristian and Burdusel Mihai.

The project was advertised by an article in Market Watch (see the link below)

http://www.marketwatch.ro/articol/11530/Studiul_interfetelor___in_structuri_oxidice_-_prioritate_de_cercetare_in_INC_DFM_pentru_urmatorii_3_ani/

Between 12 and 14 of June 2013 the NIMP team of the project will be visited by Dr. Manuel Bibes, recent winner of the E-40 award at the E-MRS conference in Strasbourg, France.

Manuel Bibes-short CV-Download

Manuel Bibes will give a seminar on 13 of June-Download

Recently the director of the project has won a long term project at the Elettra synchrotron in Trieste. The project is for 2 years period and will allow direct investigation of the ferroic interfaces by using synchtrotron radiation. the final aim of the project is to investigate the intreface between graphene and epitaxial ferroelectric layers.The project title is "In-situ investigation of ferroelectric-graphene interface formation and properties by using combined microscopy (STM) and high resolution XPS techniques with aim towards optimized, high-speed field effect devices."

The results of the project were also diseminated by comunications at international conferences. It worth to be mentioned the invited lectures that were or will be presented by the project director:

"Electric properties of epitaxial ferroelectric thin films with perovskite structure and different metals as top electrodes"

Invited at symposium O of E-MRS spring meeting, held in Strasbourg between 27 and 31 of May 2013

"Effect of interfaces on the properties of thin films and multilayers with ferroelectric properties"

Invited at symposium "Complex oxides" of the conference IC4N, to be held in Corfu, Greece, between 16 and 20 of June 2013

The project has generated new project proposals, with a marked orientation towards applications:

-"Novel generation of pyroelectric detectors based on polar semiconductors"-accepted for funding at the 2013 M-ERA net call (see https://www.m-era.net/joint-call-2013)-will start at 1 of January 2015

-"Pyroelectricity in PZT thin films and multilayers"-accepted at the 2014 IFA-CEA call (see http://www.ifa-mg.ro/cea/)-started at 1 of July 2014 (24 months)

-"Integrated – Smart Optical Sensors for Mobile AiR Testing"-submitted for Horizon 2020, call H2020-ICT-2014-1, topic ICT-26-2014, proposal number: SEP-210140423

-"Synchrotron-based spectroscopic and microscopic tools to probe graphene-like two-dimensional materials "-submitted to Graphene-Based Revolutions in ICT And Beyond (GRAPHENE Flagship, see also http://graphene-flagship.eu/?page_id=8)

-"Optimized pyroelectric materials through the polarization gradient concept and experimental model for a pyroelectric detector with potential for applications in monitoring high power/energy lasers."-Accepted at the 2013 Partnership call "PN-II-PT-PCCA-2013-4"-started at 1 of July 2014 (24 months)

The project Director was Chair of the Electroceramics XIV conference, which was held in Bucharest, at Intercontinental Hotel, between 15 and 20 of June 2014. More than 360 abstracts were submitted, and more than 300 participants from all over the world have attended the conference (see also www.electroceramics14.com for more details).

Prof. Scott during his plenary presentation at Electroceramics XIV.

The project director closing the Electroceramics XIV conference.

Between 29 of June and 4 of July the Project Director has participated to the Schechtman International Symposium held in Cancun, Mexic. The title of the invited talk:

"Interfaces in Epitaxial Structures based on Oxide Ferroelectrics"

See also http://www.flogen.org/ShechtmanSymposium/

An important moment was the visit of Prof. Albert FERT, at the invitation of the Project Director. Prof. FERT is the Nobel prize laureate for Physics in 2007. He visited the institute between 1 and 3 of October 2014.

The Project Director during the discussions at the end of the seminar presented by Prof. FERT on 2 of October 2014 in the Institute.

Project Director was co-organizer of two conferences in 201

7 th International Conference on Amorphous and Nanostructured Chalcogenides, Cluj-Napoca, 5- 10 iulie 2015 http://www.infim.ro/events/amorphous-and-nanostructured-chalcogenides-anc-7-conference

8 th International Conference on Advanced Materials (ROCAM), București, 7-10 iulie 2015 http://rocam.unibuc.ro/rocam2015/ 

In 206 he organized the first edition of the International Workshop on Advanced Materials

Presentation of professor Rodrigo Martins, former president of EMRS, present president of the Senate of EMRS

Presentation of Profesor Elvira Fortunato, vice-president of High Level Expert Group appointed as advisory body for the President of EC.