NIMP| Lucian TRUPINA, Author at NIMP

Resume

Dr. Lucian Trupina, Scientific researcher rank III (since 2014), born in 1973, graduated the Faculty of Physics at University of Bucharest (1996), has a MSc degree in Electronics Physics (1997), and a PhD degree in Physics (2013). Work experience: National Institute of Materials Physics (NIMP) (1996 – to date); work stages at the École Polytechnique Fédérale de Lausanne, Switzerland. Main areas of interest/expertise: synthesis by physical vapour deposition (sputtering, PLD) and characterization (structural, morphological, electrical and dielectric) of ferroelectric thin films down to nanometric scale by X-Ray diffraction, atomic force microscopy (AFM), impedance spectroscopy and piezoelectric force microscopy (PFM). Publications (last updated November 2022): 81 articles published in Web of Science® (WoS) journals with impact factor (e.g., Appl. Surf. Sci.; Physical Review B; Physical Review Applied, Journal of the Applied Physics); Hirsch index (WoS): 16; Citations (without self-citations): 661. Patents: 1 OSIM awarded patent (RO131881-B1/2019); Coordinated projects: NIMP Project Responsible for one international project https://infim.ro/en/project/MASTERS. Professional profile web-links: Brainmap: https://www.brainmap.ro/lucian-trupina; ORCID ID: 0000-0002-1573-5291; WoS ResearcherID: B-6802-2012.

Projects

1. Integration of new and improved materials for smart millimeter-wave sensors

Project Type: M-ERA.NET, Start Date: 2016-06-01 End Date: 2019-05-31

Publications

1. Atomically Thin MoS₂ Layers Selectively Grown on Mo Patterned Substrates for Field-Effect-Controlled Photosensors

Authors: Stavarache, I; Palade, C; Slav, A; Dascalescu, I; Lepadatu, AM; Trupina, L; Matei, E; Ciurea, ML; Stoica, T

Published: FEB 28 2024, ACS APPLIED NANO MATERIALS, 7, DOI: 10.1021/acsanm.3c05809

Selective growth of 2D MoS2 layers on patterned substrates is highly desired for easy fabrication of devices. Selectively grown 2D MoS2 on Mo patterned substrates for the formation of intimate metallic contact was obtained by a Mo-CVD method in which MoO2 from an oxidized Mo pattern and S powder are the growth precursors. Mo films were deposited by magnetron sputtering on SiO2(300 nm)/c-Si substrates and patterned by photolithography techniques for obtaining Mo strips and finger contact structures, with the gap between the strips and finger varied from 5 to 20 mu m. The filling of the gap by selectively grown atomically thin MoS2 plates of 1-2 monolayers (MLs) was demonstrated by scanning electron microscopy and atomic force microscopy imaging. Field effect devices for the characterization of the photosensitivity of selectively grown MoS2 have been fabricated from finger contact structures. The dark current is drastically reduced from 10(-9) to 10(-13)-10(-14) A by varying the gate voltage from +7 to -7 V, showing the n-type semiconductor behavior of the selectively grown 2D MoS2. High photosensitivity of 10(5) (%) was obtained for 4.5 x 10(-4) mW/cm(2) at 650 nm wavelength illumination. The spectral responsivity reaches values of 15-25 A/W at 600 nm wavelength and shows an energy onset of 1.72-1.77 eV corresponding to about 2 ML MoS2. The carrier-trapping effect responsible for the slow part of the device response can be caused by structural defects and also by adsorbed molecules like in gas sensors.

2. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films

Authors: Boni, AG; Chirila, C; Trupina, L; Radu, C; Filip, LD; Moldoveanu, V; Pintilie, I; Pintilie, L

Published: 2023 JAN 25 2023, ACS APPLIED ELECTRONIC MATERIALS, DOI: 10.1021/acsaelm.2c01497

The p-n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p-n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O-3 films doped with & AP;1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p-n homojunctions and to study their properties in relation to ferroelectric polarization. p-n and n-p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O-3 layers with different thicknesses. We find that these p-n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I-V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I-V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14-0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.

3. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.

4. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: JAN 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202205476

5. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr_0.2Ti_0.8)O₃ Thin Films

Authors: Boni, AG; Chirila, C; Trupina, L; Radu, C; Filip, LD; Moldoveanu, V; Pintilie, I; Pintilie, L

Published: 2023 JAN 25 2023, ACS APPLIED ELECTRONIC MATERIALS, DOI: 10.1021/acsaelm.2c01497

6. Experimental Band Structure of Pb(Zr,Ti)O₃: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

7. Surface charge dynamics on air-exposed ferroelectric Pb(Zr,Ti)O₃(001) thin films

Authors: Abramiuc, LE; Tanase, LC; Prieto, MJ; Caldas, LD; Tiwari, A; Apostol, NG; Husanu, MA; Chirila, CF; Trupina, L; Schmidt, T; Pintilie, L; Teodorescu, CM

Published: AUG 10 2023, NANOSCALE, 15, DOI: 10.1039/d3nr02690f

Probing of the free surface ferroelectric properties of thin polar films can be achieved either by estimating the band bending variance under the top-most layer or by studying the extent of the extrinsic charge accumulated outside the surface. Photoemitted or incoming low-energy electrons can be used to characterize locally both properties in a spectromicroscopic approach. Thin ferroelectric lead zirco-titanate (PZT) is investigated by combining low energy/mirror electron microscopy (LEEM/MEM) with photoemission electron microscopy (PEEM) and high-resolution photoelectron spectroscopy (XPS). Significant extrinsic negative compensation charge is proven to accumulate on the surface of the outward polarized thin film, indicated by high MEM-LEEM transition values, up to 15.3 eV, and is correlated with the surface electrostatic potential, which can be partially screened either by electrons interacting with the sample or by soft X-rays through the ejection of secondary electrons and generation of positive charge under the surface. A radiation-induced surface charge compensation effect is observed. The study indicates that air-exposed high quality ferroelectric thin films show large negative surface potentials, determined locally on the surface, which are nevertheless sensitive to beam damage and molecular desorption. These values represent a confirmation of previously estimated surface potential energy values determined from the LEED data on clean surfaces.

8. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films

Authors: Boni, AG; Chirila, C; Trupina, L; Radu, C; Filip, LD; Moldoveanu, V; Pintilie, I; Pintilie, L

Published: JAN 2023, ACS APPLIED ELECTRONIC MATERIALS, DOI: 10.1021/acsaelm.2c01497

9. Pulsed laser deposited V2O3 thin-films on graphene/aluminum foil for micro-battery applications

Authors: Tite, T; Ungureanu, C; Buga, M; Stavarache, I; Matei, E; Negrila, CC; Trupina, L; Spinu-Zaulet, A; Galca, AC

Published: MAR 15 2023, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 933, 117290, DOI: 10.1016/j.jelechem.2023.117290

The development of new thin-film cathodes triggered a recent research interest in energy storage applications. Over the past years, vanadium oxides have been extensively explored as promising electrodes for batteries owing to their rich valence states and remarkable electrochemical properties. Herein, we report on the synthe-sis of undoped and Sn doped V2O3 thin-films on graphene (G)/Al foil by pulsed laser deposition followed by rapid thermal annealing in N2 at low temperature (similar to 430 degrees C). The obtaining V2O3 phase on graphene/Al foil (G/Al) has been confirmed by X-ray diffraction and Raman and X-ray photoelectron spectroscopy analyses. The synthesized vanadium oxide films were tested as cathodes in coin cells. The electrochemical properties have been systematically investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) measurements. A superior electrochemical performance was observed for the V2O3 on G/Al structures, with an initial capacity of around 300 mAh g-1, with respect to the bare G/Al electrode. The use of the Sn-doped (5 mol%) V2O3 thin-films improved slightly the initial capac-ity up to a value of ca. 311 mAh g-1. Both V2O3/G/Al and Sn-doped V2O3/G/Al exhibited excellent cycling performances after 40 cycles with a capacity maintenance at a C-rate C/20 of 317 mAh g-1. Long-term cycling test (up to 200 cycles) showed that the Sn doping could be an excellent strategy to improve the stability of the electrodes, which yielded a capacity loss of only 0.128% per cycle. Possible mechanisms are presented and dis-cussed. This work could serve as point of reference for future developments in the field of batteries employing vanadium oxide-based thin-films deposited by physical vapor deposition techniques.

10. Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O-3 films through Nb (n-type) and Fe (p-type) doping

Authors: Chirila, CF; Stancu, V; Boni, GA; Pasuk, I; Trupina, L; Filip, LD; Radu, C; Pintilie, I; Pintilie, L

Published: JAN 14 2022, SCIENTIFIC REPORTS, 12, 755, DOI: 10.1038/s41598-022-04802-1

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

11. Magnetic Properties of Nanosized Fe and FeCo Systems on Trenched Mo Templates

Authors: Stanciu, AE; Schinteie, G; Kuncser, AC; Locovei, C; Trupina, L; Iacob, N; Leca, A; Borca, B; Kuncser, V

Published: SEP 2022, COATINGS, 12, 1366, DOI: 10.3390/coatings12091366

The manipulation of magnetic anisotropy represents the fundamental prerequisite for the application of magnetic materials. Here we present the vectorial magnetic properties of nanostructured systems and thin films of Fe and FeCo prepared on linearly trenched Mo templates with thermally controlled periodicity. The magnetic properties of the nanosystems are engineered by tuning the shape, size, thickness, and composition parameters of the thin films. Thus, we control coercivity, magnetization, orientation of the easy axis of magnetization, and the long-range magnetic order of the system in the function of the temperature. We distinguish magnetic components that emerge from the complex morpho-structural features of the undulating Fe or FeCo nanostructured films on trenched Mo templates: (i) assembly of magnetic nanowires and (ii) assembly of magnetic islands/clusters. Uniaxial anisotropy at room temperature was proven, characterized, and explained in the case of all systems. Our work contributes to the understanding of magnetic properties necessary for possible further applications of linear systems and undulated thin films.

12. Accidental Impurities in Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films Grown by Pulsed Laser Deposition and Their Impact on the Macroscopic Electric Properties

Authors: Boni, GA; Chirila, CF; Stancu, V; Amarande, L; Pasuk, I; Trupina, L; Istrate, CM; Radu, C; Tomulescu, A; Neatu, S; Pintilie, I; Pintilie, L

Published: MAY 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11051177

Structural and electrical properties of epitaxial Pb(Zr0.2Ti0.8)O-3 films grown by pulsed laser deposition from targets with different purities are investigated in this study. One target was produced in-house by using high purity precursor oxides (at least 99.99%), and the other target was a commercial product (99.9% purity). It was found that the out-of-plane lattice constant is about 0.15% larger and the a domains amount is lower for the film grown from the commercial target. The polarization value is slightly lower, the dielectric constant is larger, and the height of the potential barrier at the electrode interfaces is larger for the film deposited from the pure target. The differences are attributed to the accidental impurities, with a larger amount in the commercial target as revealed by composition analysis using inductive coupling plasma-mass spectrometry. The heterovalent impurities can act as donors or acceptors, modifying the electronic characteristics. Thus, mastering impurities is a prerequisite for obtaining reliable and reproducible properties and advancing towards all ferroelectric devices.

13. Effect of strain and stoichiometry on the ferroelectric and pyroelectric properties of the epitaxial Pb(Zr0.2Ti0.8)O-3 films deposited on Si wafers

Authors: Chirila, C; Boni, GA; Filip, LD; Husanu, M; Neatu, S; Istrate, CM; Le Rhun, G; Vilquin, B; Trupina, L; Pasuk, I; Botea, M; Pintilie, I; Pintilie, L

Published: APR 2021, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 266, DOI: 10.1016/j.mseb.2021.115042

Properties of epitaxial PbZr0.2Ti0.8O3 (PZT) films deposited on Si substrates were investigated for integration in the present CMOS technology. Polarization is downward oriented, in association with the presence of an internal electric field, and has a lower value compared to the PZT films deposited on single crystal perovskite SrTiO3 (STO) substrates (40 mu C/cm(2) versus 80 mu C/cm(2)), while the dielectric constant is larger (180 versus 120). Large value for the pyroelectric coefficient was also found, 1.22 x 10(-3)C/m(2)K, as for PZT grown on single crystal STO. The macroscopic ferroelectric and pyroelectric properties appear to be affected by the structural quality and stoichiometry of the PZT film. The changes in the electric properties are an effect of the strain gradients induced by the large difference between the thermal expansion coefficients of PZT and Si substrate, leading in turn to Pb oxidation and antisite defect formation compared to PZT films deposited on STO substrates.

14. Homogeneous versus Inhomogeneous Polarization Switching in PZT Thin Films: Impact of the Structural Quality and Correlation to the Negative Capacitance Effect

Authors: Pintilie, L; Boni, GA; Chirila, CF; Stancu, V; Trupina, L; Istrate, CM; Radu, C; Pintilie, I

Published: AUG 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11082124

Polarization switching in ferroelectric films is exploited in many applications, such as non-volatile memories and negative capacitance field affect transistors. This can be inhomogeneous or homogeneous, depending on if ferroelectric domains are forming or not during the switching process. The relation between the polarization switching, the structural quality of the films and the negative capacitance was not studied in depth. Here, Pb(Zr0.2Ti0.8)O-3 (PZT) layers were deposited by pulse laser deposition (PLD) and sol-gel (SG) on single crystal SrTiO3 (STO) and Si substrates, respectively. The structural quality was analyzed by X-ray diffraction and transmission electron microscopy, while the electric properties were investigated by performing hysteresis, dynamic dielectric measurements, and piezo-electric force microscopy analysis. It was found that the PZT layers grown by PLD on SRO/STO substrates are epitaxial while the layers deposited by SG on Pt/Si are polycrystalline. The polarization value decreases as the structure changes from epitaxial to polycrystalline, as well as the magnitude of the leakage current and of the differential negative capacitance, while the switching changes from homogeneous to inhomogeneous. The results are explained by the compensation rate of the depolarization field during the switching process, which is much faster in epitaxial films than in polycrystalline ones.

15. Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

Authors: Patru, RE; Khassaf, H; Pasuk, I; Botea, M; Trupina, L; Ganea, CP; Pintilie, L; Pintilie, I

Published: AUG 2021, MATERIALS, 14, DOI: 10.3390/ma14154215

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes' interfaces.

16. Electro-active properties of nanostructured films of cytosine and guanine nucleobases

Authors: Socol, M; Trupina, L; Galca, AC; Chirila, C; Stan, GE; Vlaicu, AM; Stanciu, AE; Boni, AG; Botea, M; Stanculescu, A; Pintilie, L; Borca, B

Published: OCT 8 2021, NANOTECHNOLOGY, 32, DOI: 10.1088/1361-6528/ac10e4

The discovery of multifunctional properties related to electro-activity of organic systems of biomolecules is important for a variety of applications, especially for devices in the realm of biocompatible sensors and/or bioactuators. A further step towards such applications is to prepare thin films with the required properties. Here, the investigation is focused on the characterization of films of guanine and cytosine nucleobases, prepared by thermal evaporation-an industrial accessible deposition technique. The cytosine films have an orthorhombic non-centrosymmetric structure and grow in two interconnected nanostructured fractal patterns, of nearly equal proportion. Piezoresponse force microscopy images acquired at room temperature on the cytosine films display large zones with antiparallel alignment of the vertical components of the polarization vector. Guanine films have a dense nano-grained morphology. Our studies reveal electrical polarization switching effects which can be related to ferroelectricity in the films of guanine molecules. Characteristic ferroelectric polarization-electric-field hysteresis loops showing large electrical polarization are observed at low temperatures up to 200 K. Above this temperature, the guanine films have a preponderant paraelectric phase containing residual or locally induced nano-scopic ferroelectric domains, as observed by piezoresponse force microscopy at room temperature.

17. CO adsorption, reduction and oxidation on Pb(Zr,Ti)O-3(001) surfaces associated with negatively charged gold nanoparticles

Authors: Apostol, NG; Husanu, MA; Lizzit, D; Hristea, IA; Chirila, CF; Trupina, L; Teodorescu, CM

Published: APR 15 2021, CATALYSIS TODAY, 366, 154, DOI: 10.1016/j.cattod.2020.02.042

Gold is deposited on atomically clean, inwards polarized, ferroelectric lead zirco-titanate deposited by pulsed laser deposition on strontium titanate (001) single crystal, then carbon monoxide adsorption and desorption experiments are investigated by in situ fast photoelectron spectroscopy using synchrotron radiation. Atomic force microscopy and high resolution photoelectron spectroscopy are consistent with the formation of 50?100 nm nanoparticles, and their Au 4f core levels point to a negative charge state of gold. As compared with a similar experiment performed on ferroelectric lead zirco-titanate with similar polarization state and without gold, the saturation coverage after exposure to carbon monoxide increases by about 68 %, and also most of the additional carbon is found in oxidized state. Desorption experiments with in situ follow-up by photoelectron spectroscopy are performed as function of temperature, and the neutral carbon intensity decreases when the ferroelectric polarization decreases, while the components corresponding to oxidized carbon remain unchanged. It looks that neutral carbon adsorption is strictly related to the polarization of the ferroelectric film, while carbon still found in molecular form is related to its carbonyl bonding on metal nanoparticles, independent of the polarization state of the substrate. Desorbed carbon at higher temperature uptakes oxygen from the substrate.

18. Investigation of Ba0.6Sr0.4TiO3 thick films by means of a novel THz-TDS approach

Authors: Nedelcu, L; Annino, G; Chirila, C; Trupina, L; Galca, AC; Banciu, MG

Published: MAR 15 2020, APPLIED SURFACE SCIENCE, 506, DOI: 10.1016/j.apsusc.2019.144807

Ba0.6Sr0.4TiO3 (BST) ferroelectric thick films were grown on MgO(001) and Al2O3 (0 0 0 1) single-crystal substrates by using a pulsed laser deposition method. Structural, morphological, optical, and terahertz characterization of the BST films were performed by X-ray Diffraction, Atomic Force Microscopy, Spectroscopic Ellipsometry (SE), and Terahertz Time-Domain Spectroscopy (THz-TDS). Single-phase samples with strong preferred (1 1 1) orientation and surface roughness lower than 1.5% of their thicknesses have been obtained for both types of substrates. SE was employed to extract the thickness and optical properties by using a 3-layer optical model (substrate/thin film/roughness). The inferred refractive index @630 nm is around 2.05, while the optical interference is visible until 3.3 eV. The THz-TDS measurements in transmission set-up were carried out one after the other on substrates before and after the BST film deposition. The standard THz-TDS analysis of double-layer samples proved difficult to complete in the cases in which a thin or thick film is deposited on a much thicker substrate of known dielectric properties. However, we have been able to extract the complex dielectric permittivity in the THz domain for BST samples with thicknesses of few microns, by developing a specific procedure of data analysis.

19. Unexpected magneto-functionalities of amorphous Fe-Gd thin films crossing the magnetization compensation point

Authors: Stanciu, AE; Schinteie, G; Kuncser, A; Iacob, N; Trupina, L; Ionita, I; Crisan, O; Kuncser, V

Published: MAR 15 2020, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 498, DOI: 10.1016/j.jmmm.2019.166173

A complex investigation of the morpho-structural, magnetic, magneto-optical and magneto-transport properties of amorphous Fe-Gd thin films crossing the magnetization compensation point is reported and the unexpected observed magneto-functionalities are discussed. A tendency of magnetic domain formation with increasing the Fe content over the compensation concentration is observed. The switch from a reversed Magneto-optical Kerr Effect loop to a direct loop when increasing the Fe content over the compensation point is explained via the specific contribution to the rotation of the polarization vector from each magnetic sublattice, belonging to Fe and Gd, respectively. Local atomic configurations and magnetic interactions ascertained the amorphous character and revealed an out-ofplane orientation of the magnetic moment of Fe above the compensation point. The thermomagnetic curves prove a concentration dependent behavior, explained by weakly coupled magnetization relaxation processes of the two magnetic sub-lattices. On the other hand, the magnetic hysteresis loops gave evidence of two exchange coupled magnetic phases with different coercive fields. According to structural and Fe-57 Mossbauer Spectroscopy results, the two phases correspond to definite nanosized volumes of two different average concentrations (one of them closer to the compensation point) which are randomly distributed in the film. The unexpected single step-like behavior of the magneto-resistivity curves was explained by dissimilar switching of the spins in these two magnetic phases distributed in nano-sized volumes.

20. Polarization Switching and Negative Capacitance in Epitaxial PbZr0.2Ti0.8O3 Thin Films

Authors: Pintilie, L; Boni, GA; Chirila, C; Hrib, L; Trupina, L; Filip, LD; Pintilie, I

Published: JUL 27 2020, PHYSICAL REVIEW APPLIED, 14, DOI: 10.1103/PhysRevApplied.14.014080

The negative-capacitance effect in devices based on combined ferroelectric-dielectric gate oxides is thought to be a potential solution to break free from the so-called Boltzmann tyranny. To lower the power consumption in field-effect transistors, the subthreshold swing factor S should be reduced below the ther-modynamic limit of 60 mV per decade. Yet, despite numerous studies dedicated to this effect in the past decade, its origin in ferroelectric capacitors or ferroelectric-based superlattices remains unclear, being considered either a transitory product of polarization switching or an intrinsic phenomenon related to the presence of ferroelectric polarization. In this study it is shown, starting from simple electrostatic con-siderations, that negative capacitance is present during polarization switching and is accompanied by a significant increase of the current flowing through the ferroelectric capacitor. Coupled with piezo-force microscopy results, it is shown that the polarization orientation suddenly changes at the coercive voltage, accompanied by a complete reconfiguration of the potential barriers at the Schottky-like contacts present at the electrode-ferroelectric interfaces. A method to estimate the polarization-switching time, as the time associated with the presence of the negative-capacitance effect, is proposed. Values in the range from 100 to 1000 ns are obtained for epitaxial PbZr0.2Ti0.8O3 films. These findings suggest that negative capacitance may be an intrinsic effect in ferroelectrics but that it is a transitory effect, present only when ferroelectric polarization passes through zero (switching).

21. Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

Authors: Trupina, L; Nedelcu, L; Banciu, MG; Crunteanu, A; Huitema, L; Constantinescu, C; Boulle, A

Published: FEB 2020, JOURNAL OF MATERIALS SCIENCE, 55, 1764, DOI: 10.1007/s10853-019-04004-7

Iridium thin films are grown by direct-current plasma magnetron sputtering, on MgO single-crystal substrates with various surface orientations, i.e. (100), (111), and (110). The surface morphology, the crystalline properties of the films, and the substrate-thin-film interface are investigated by atomic force microscopy, X-ray diffraction (XRD), focused ion beam scanning electron microscopy, and high-resolution transmission electron microscopy, respectively. The results reveal that hetero-epitaxial thin films with different crystallographic orientation and notable atomic scale smooth surface are obtained. From the XRD analysis, the following epitaxial relations are obtained: (1) (100)(Ir)||(100)(MgO) out-of-plane and [001](Ir)||[001](MgO) in-plane for Ir grown on MgO(100), (2) (110)(Ir)||(110)(MgO) out-of-plane and [1-10](Ir)||[1-10](MgO) in-plane for Ir grown on MgO(110), and (3) (111)(Ir)||(111)(MgO) out-of-plane and two variants for in-plane orientation [1-10](Ir)||[1-10](MgO) and [1-10](Ir)||[10-1](MgO), respectively, for Ir grown on MgO(111). Because of the large misfit strain (9.7%), the thin films are found to grow in a strain-relaxed state with the formation of geometrical misfit dislocations with a similar to 2.8-nm spacing, whereas thermal strain is stored upon cooling down from the growth temperature (600 degrees C). The best structural characteristics are obtained for the (111)-oriented films with a mosaicity of 0.3 degrees and vanishingly small lattice distortions. The (100)- and (110)-oriented films exhibit mosaicities of similar to 1.2 degrees and lattice distortions of similar to 1% which can be explained by the larger surface energy of these planes as compared to (111).

22. Polarization-dependent magnetism of the Ni/BaTiO3 interface

Authors: Bocirnea, AE; Popescu, DG; Chirila, C; Costescu, RM; Kuncser, V; Stancu, V; Trupina, L; Pasuk, I; Vlaicu, AM; Husanu, MA

Published: MAR 4 2020, PHYSICAL REVIEW MATERIALS, 4, DOI: 10.1103/PhysRevMaterials.4.034402

We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO3(001) heterostructures and demonstrate the modulation of the magnetism and incidence of exchange bias in the ultrathin metallic Ni overlayer, depending on the ferroelectric state of the bottom layer. We establish that 5-nm-thick monocrystalline Ni film deposited on BaTiO3 with ferroelectric polarization pointing towards the surface (P+) favors the organization of Ni into uniform ferromagnetic domains. Ni grown on BaTiO3 with opposite ferroelectric polarization is featured by emerging exchange-bias coupling between the ferromagnetic Ni top layers and the antiferromagnetic reacted interface, as theoretically explained by first-principles calculations. We explicitly obtain the morphology of the magnetic domains of the crystalline Ni layer in atomic and magnetic force microscopy measurements (AFM/MFM). The resemblance of AFM and MFM images indicate that, although with radically different morphologies, in both cases all spins orient in the Ni plane. Consequently, the distinct signature of the ferroelectric-ferromagnetic coupling extracted from the magneto-optical Kerr effect measurements encodes all the information of sample magnetism. The peculiar magnetic coupling depending on the ferroelectric state indicates new ways of engineering the functionality of metal/ferroelectric interfaces.

23. Room temperature ferromagnetism and its correlation to ferroelectricity of manganese embedded in lead zirco-titanate

Authors: Bucur, IC; Apostol, NG; Abramiuc, LE; Tanase, LC; Tache, CA; Lungu, GA; Costescu, RM; Chirila, CF; Trupina, L; Pintilie, L; Teodorescu, CM

Published: JAN 1 2019, THIN SOLID FILMS, 669, DOI: 10.1016/j.tsf.2018.11.018

Manganese is deposited at high temperature on (001) oriented ferroelectric lead zirco-titanate prepared in two different ways: sputter-annealed or just simply annealed in ultrahigh vacuum. Room temperature ferromagnetism (FM) is obtained for Mn deposited on sputter-annealed substrates, while for the other sample preparation a paramagnetic behaviour is obtained. Also, for the first case a clear inwards component of the polarization P( - ) is observed by X-ray photoelectron spectroscopy and piezoresponse force microscopy. Composition analysis evidenced formation of Pb vacancies in the case of FM - P(( - ) )sample, consistent with hole formation near the surface, needed both to stabilize the inwards polarization state and to intermediate ferromagnetism between Mn2+ ions. The indirect exchange ferromagnetism mediated by holes is stronger, most probably because the interaction energy is proportional with the carrier effective mass. Also, whereas in the case of unsputtered substrate a stable surface Mn oxide is formed, defect formation by sputtering seems to favor Mn migration inside the sample. This also induces the formation of a thin film where ferromagnetism and the orientation of ferroelectric polarization might have the same origin, i. e. holes accumulated near the outer surface.

24. Frequency selective surfaces with hexagonal elements for millimeter waves applications

Authors: Banciu, MG; Geambasu, DC; Nedelcu, L; Trupina, L

Published: 2019, 2019 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2019), 42ND EDITION, 64, DOI:

Numerical investigations on a frequency selective surface using metalized strips deposited on high resistive silicon in a millimeter waves are presented in this paper. High resistivity Si substrate was chosen due to the very good transparence in millimeter waves. For simulations, normal incidence of millimeter waves alongside Floquet modes and ports are considered. Dependence of the frequency response with the geometrical parameters of the unit cell is discussed.

25. EXPERIMENTAL STUDY OF TERAHERTZ RESPONSE FROM SOME FERROELECTRIC AND DIELECTRIC MATERIALS

Authors: Banciu, MG; Nedelcu, L; Furuya, T; Hrib, L; Geambasu, DC; Trupina, L; Pantelica, D; Mihai, MD; Tani, M

Published: OCT-DEC 2019, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 20, 360, DOI:

Barium strontium titanate (BST) ferroelectric layers were deposited on high resistivity Si substrates by Pulsed Laser Deposition and Radio Frequency sputtering. The stoichiometry was measured by using the Rutherford Backscattering technique at 3.041 MeV. For sub-THz measurements of Si samples, a new resonant method placing the sample between two flanged waveguides is proposed. In the THz range, the Time Domain Spectroscopy proved to be a reliable method. Both methods show effects due to the dielectric losses of BST in that frequency range.

26. Memcomputing and Nondestructive Reading in Functional Ferroelectric Heterostructures

Authors: Boni, GA; Filip, LD; Chirila, C; Iuga, A; Pasuk, I; Hrib, L; Trupina, L; Pintilie, I; Pintilie, L

Published: AUG 26 2019, PHYSICAL REVIEW APPLIED, 12, DOI: 10.1103/PhysRevApplied.12.024053

Multiple nonvolatile and well-separated capacitive states can be obtained in a two-terminal ferroelectric capacitor setup by fine tuning the polarization switching process. This approach allows for the implementation of memcomputing (same platform for storage and computing) capable ferroelectric structures. Digital and analog storage modes are exemplified in this work together with an algorithm for simple binary computation functions such as OR/NOR and AND/NAND for data processing on the same device. Results are obtained by controlling the polarization switching process in ferroelectric multi-layers such as Pb (Zr0.2Ti0.8)O-3/SrTiO3/Pb (Zr0.2Ti0.8)O-3 and Pb (Zr0.2Ti0.8)O-3/BaTiO3/Pb (Zr0.2Ti0.8)O-3. Besides memcomputing, these results can be used for nondestructive capacitive reading of information in simple ferroelectric capacitors or can open the way toward applications such as neuromorphic and chaotic circuits.

27. Structural, electric and pyroelectric properties of up and down graded PZT multilayers

Authors: Botea, M; Hrib, L; Pasuk, I; Iuga, A; Trupina, L; Negrea, R; Becherescu, N; Pintilie, L

Published: JUL 2019, CURRENT APPLIED PHYSICS, 19, 810, DOI: 10.1016/j.cap.2019.04.010

Multi-layered structures, composed of thin films from materials with different compositions or physical properties, represents a way to obtain enhanced properties or even new functionalities. In this work, lead zirconate titanate PbZrxTi1-xO3 (PZT; x = 0.20, 0.52, 0.80) multilayers were grown by pulsed laser deposition (PLD) on a single crystal strontium titanate (SrTiO3, STO) substrate, using a strontium ruthenate (SrRuO3, SRO) film as buffer layer for epitaxial growth, and also as back electrode. Up and down multi-layers were grown and their physical and structural properties were compared, up being the structure in which Zr concentration was varied from 20% near the STO substrate to 80% at the surface, while down is for the structure in which the Zr concentration starts with 80% near the substrate and ends with 20% at the surface. It was found that the electric and pyroelectric properties of the two graded structures are significantly different. The up structure presents electric properties that are comparable with those of single composition PZT films while the properties of the down structure are deteriorated, especially in terms of the leakage current magnitude. Pyroelectric signal could be measured only for the up structure. These differences were attributed to larger density of structural defects in the down structure compared to the up one. This is due to the different growth sequence: Lop structure starts with tetragonal PZT on cubic substrate (lower lattice mismatch, 1.1%) while down structure starts with rhombohedral PZT on cubic substrate (larger lattice mismatch, almost 5%).

28. Triggering surface ferroelectric order in Pb(Zr, Ti)O-3(001) by deposition of platinum

Authors: Bucur, IC; Tanase, LC; Abramiuc, LE; Lungu, GA; Chirila, C; Trupina, L; Apostol, NG; Costescu, RM; Negrea, RF; Pintilie, L; Teodorescu, CM

Published: FEB 28 2018, APPLIED SURFACE SCIENCE, 432, DOI: 10.1016/j.apsusc.2017.04.238

By platinum deposition on a 150 nm thick film of lead zirco-titanate oriented PZT(001), grown on strontium titanate (001) single crystals with a strontium ruthenate buffer layer, which did not show initial preferential out-of-plane orientation of its ferroelectric polarization, a band bending near the interface towards lower energies is observed using photoelectron spectroscopy, by following all core levels from the substrate (Pb 4f, Zr 3d, Ti 2p, O 1s). This is unexpected given the fact that platinum has a larger work function than PZT and a rectifying contact for electrons is expected to be built at the interface. This observation may have two explanations: (i) platinum forms an alloy with elements from PZT yielding a metal with considerable lower work function; (ii) platinum provides electrons to the substrate which are able to compensate the depolarization field generated by the outwards polarization state. Several arguments are brought in favor of the second hypothesis, especially the attenuation of core levels from the substrate which is well described by exponential functions with reasonable values of the photoelectron inelastic mean free path, suggesting the formation of a sharp interface. High resolution transmission electron microscopy confirmed the sharpness of the interface. (C) 2017 Elsevier B.V. All rights reserved.

29. Polarization Orientation in Lead Zirconate Titanate (001) Thin Films Driven by the Interface with the Substrate

Authors: Tanase, LC; Abramiuc, LE; Popescu, DG; Trandafir, AM; Apostol, NG; Bucur, IC; Hrib, L; Pintilie, L; Pasuk, I; Trupina, L; Teodorescu, CM

Published: SEP 11 2018, PHYSICAL REVIEW APPLIED, 10, DOI: 10.1103/PhysRevApplied.10.034020

We investigate the effect of the nature of the substrate and the bottom interface on the out-of-plane polarization orientation of ultrathin (10-nm) lead zirconate titanate (PZT) thin films of (001) orientation by photoelectron spectroscopy of samples without surface contamination. The substrate nature is varied between insulator (strontium titanate, STO) and semiconductor (Nb-doped STO, STON) and finally to a metal with a work function lower than that of PZT (strontium ruthenate, SRO). Outward polarization is obtained for PZT/STON(001) and inward polarization is obtained for PZT/STO(001) and PZT/SRO(001). Explanations are given for all these typical cases, the main elements being charge accumulation for compensation of the depolarization field, self-doping of PZT films, and the interface electric field driving the orientation of the polarization of the ferroelectric films. We find p-type self-doping is correlated with the inward polarization, and the driving field is formed between a negatively charged region with negatively ionized acceptors near the interface with the substrate and the p-type degenerate region with holes accumulated inside, toward the surface. This mechanism may be reversed under the assumption of n-type self-doping, positively ionized donors near the interface, and accumulated electrons toward the surface in the case of an interface with a substrate with a higher work function, being in line with recent data (PZT/Pt or BaTiO3/SRO).

30. Millimeter wave and Terahertz investigations on some dielectric materials

Authors: Banciu, MG; Furuya, T; Geambasu, DC; Nedelcu, L; Pantelica, D; Dracea, MD; Ionescu, P; Iuga, A; Chirila, C; Hrib, L; Trupina, L; Tani, M

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 290, DOI:

Investigations of barium strontium titanate (BST) layers deposited on MgO and Si substrates are presented. Since the Sr content determines the dielectric and optical properties of the BST layers at room temperature, accurate compositional analysis was performed by using Rutherford Backscattering technique at 3.041 Mev.

31. 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)).

32. Microwave antenna array using new dielectric resonator antenna elements

Authors: Banciu, MG; Militaru, N; Martian, A; Nicolaescu, I; Tuta, L; Geambasu, DC; Nedelcu, L; Trupina, L; Ramer, R

Published: 2017, 2017 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 40TH EDITION, 132, DOI:

Investigations on antenna array for 5.8 GHz frequency band applications are presented in this paper. In order to enhance the characteristics of the dielectric resonator antenna elements, a pair of resonators with different sizes and dielectric constants is used. The antenna elements are connected to four daughter-boards of Universal Software Radio Peripherals, which perform the signal processing required by the sources detection and beamforming.

33. Low-energy electron diffraction from ferroelectric surfaces: Dead layers and surface dipoles in clean Pb(Zr, Ti)O-3(001)

Authors: Teodorescu, CM; Pintilie, L; Apostol, NG; Costescu, RM; Lungu, GA; Hrib, L; Trupina, L; Tanase, LC; Bucur, IC; Bocirnea, AE

Published: SEP 19 2017, PHYSICAL REVIEW B, 96, 115438, DOI: 10.1103/PhysRevB.96.115438

The positions of the low energy electron diffraction (LEED) spots from ferroelectric single crystal films depend on its polarization state, due to electric fields generated outside of the sample. Onemay derive the surface potential energy, yielding the depth where the mobile charge carriers compensating the depolarization field are located (delta). On ferroelectric Pb(Zr, Ti)O-3(001) samples, surface potential energies are between 6.7 and 10.6 eV, and d values are unusually low, in the range of 1.8 +/- 0.4 angstrom. When delta is introduced in the values of the band bending inside the ferroelectric, a considerably lower value of the dielectric constant and/or of the polarization near the surface than their bulk values is obtained, evidencing either that the intrinsic 'dielectric constant' of the material has this lower value or the existence of a 'dead layer' at the free surface of clean ferroelectric films. The inwards polarization of these films is explained in the framework of the present considerations by the formation of an electron sheet on the surface. Possible explanations are suggested for discrepancies between the values found for surface potential energies from LEED experiments and those derived from the transition between mirror electron microscopy and low energy electron microscopy.

34. Polarization landscape effects in soft X-ray-induced surface chemical decomposition of lead zirco-titanate, evidenced by photoelectron spectromicroscopy

Authors: Abramiuc, LE; Tanase, LC; Barinov, A; Apostol, NG; Chirila, C; Trupina, L; Pintilie, L; Teodorescu, CM

Published: AUG 21 2017, NANOSCALE, 9, 11067, DOI: 10.1039/c7nr03003g

The stability of thin films of lead zirco-titanate (PZT) under intense soft X-ray beams is investigated by time-resolved photoelectron spectromicroscopy with a lateral resolution below 1 micrometer. Surface dissociation is observed when samples are irradiated with intense (5 x 10(23) photons per s per m(2)) soft X-rays, with promotion of reduced lead on the surface. On areas exhibiting outwards polarization (P(+)), the reduced lead is formed at the expense of P(+)-PZT. On areas presenting co-existing P(+) states with areas without out-of-plane polarization (P-(0)), the reduced lead is formed at the expense of the P-(0)-PZT component, while the P(+)-PZT remains constant. The main dissociation mechanism was found to be triggered by 'hot' electrons in the conduction band, with energies exceeding the surface dissociation energies. Dissociation occurs basically when the electron affinity is larger than the dissociation energy of PbO (for P(+) areas) or PbO- (for P-(0) areas). Such mechanisms may be adapted for dissociation of other molecules on surfaces of ferroelectric thin films or for quantifying the stability of ferroelectric surfaces interacting with other radiation, with applications in the fields of photocatalysis or photovoltaic devices.

35. Relation between domain structure and pyroelectric response in as-grown epitaxial Pb(Zr0.2Ti0.8)O-3 thin films on substrates with different resistivity

Authors: Pintilie, I; Trinca, L; Trupina, L; Pasuk, I; Pintilie, L

Published: SEP 2017, MATERIALS RESEARCH BULLETIN, 93, 207, DOI: 10.1016/j.materresbull.2017.04.054

Epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films were grown by pulsed laser deposition on two slightly different types of single crystal substrates, namely SrTiO3 (STO) buffered with a thin layer of conductive SrRuO3 (SRO), and SrTiO3 doped with 0.5% Nb (STON). Although self-poling effect was expected in both cases, due to the compressive strain imposed by the substrate, it was found that the pyroelectric response of as grown samples is with about two orders of magnitude larger for the PZT film deposited on SRO/STO compared to the one deposited on STON substrate. In order to explain the finding, the electrical properties were investigated and it was found that the quantities involved in the equation giving the magnitude of the pyroelectric signal, namely dielectric constant and electrical resistivity, have about the same values Therefore, the different pyroelectric response in the as-grown samples was explained by different structure of ferroelectric domains induced by the different carrier concentration in the two substrates: 90 degrees domains for PZT on SRO/STO and 180 degrees domains for PZT on STON. It appears that the resistivity of the substrate and its ability to compensate the depolarization field affect the domain structure, with impact on the pyroelectric response, although the strain conditions are similar in both cases. The trying to increase the pyroelectric response for the PZT film deposited on STON substrate by applying a poling process was not successful, as the 180 degrees domain structure restores shortly after removing the poling field. (C) 2017 Elsevier Ltd. All rights reserved.

36. Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces

Authors: Tanase, LC; Apostol, NG; Abramiuc, LE; Tache, CA; Hrib, L; Trupina, L; Pintilie, L; Teodorescu, CM

Published: OCT 14 2016, SCIENTIFIC REPORTS, 6, DOI: 10.1038/srep35301

Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(-), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(-) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(-) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(-) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface.

37. Ultra-High Tunability of Ba(2/3)Sr(1/3) TiO3-Based Capacitors Under Low Electric Fields

Authors: Ghalem, A; Rammal, M; Huitema, L; Crunteanu, A; Madrangeas, V; Dutheil, P; Dumas-Bouchiat, F; Marchet, P; Champeaux, C; Trupina, L; Nedelcu, L; Banciu, MG

Published: JUL 2016, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 26, 506, DOI: 10.1109/LMWC.2016.2576455

We report the high-frequency electrical characterization of Ba2/3Sr1/3 TiO3 (BST) thin films exhibiting a very high dielectric tunability with low losses at 2.45 GHz under very low applied electrical fields. BST layers were integrated in out-of-plane Metal-Insulator-Metal (MIM) devices with optimized Ir/MgO(100) bottom electrodes. The high frequency properties of BST films with thicknesses of 200 nm, 450 nm and 1450 nm were thoroughly investigated in the 100 MHz-10 GHz domain and exhibit extremely high capacitance tuning abilities of 82%, 81% and 70% respectively, under applied voltages as low as 10 V. MIM devices responses show the onset of acoustic resonances associated with the BST electrostrictive behavior under an electric field. By combining high tunability with low resistive losses under low applied voltages, these devices are opening promising avenues for their integration in high-performance tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used ISM (industrial, scientific and medical) frequency band.

38. XPS Analysis of AuGeNi/Cleaved GaAs(110) Interface

Authors: Negrila, CC; Lazarescu, MF; Logofatu, C; Cotirlan, C; Ghita, RV; Frumosu, F; Trupina, L

Published: 2016, JOURNAL OF NANOMATERIALS, 2016, DOI: 10.1155/2016/7574526

The depth composition of the thin layer alloy, AuGeNi, devoted to acting as an ohmic contact on n-GaAs(110) has been investigated by in situ XPS combined with Argon ion sputtering techniques. The fresh cleaved surfaces, supposed to be free of oxygen, were usually deposited with a 200nm metallic layer in high vacuum conditions (better than 10(-7) torr), by thermal evaporation, and annealed at a 430-450 degrees Celsius temperature for 5 minutes. About 18 sessions of ion Ar surfaces etching and intermediate XPS measurements were performed in order to reveal the border of the metal/semiconductor interface. The atomic concentrations of the chemical elements have been approximated. Au4f, Ga3d, Ga2p, As3d, As2p, Ni2p(3/2), Ge3d, O1s, and C1s spectral lines were recorded. The Au, Ge, and Ni have a homogenous distribution while Ga and As tend to diffuse to the surface. Oxygen is present in the first layers of the surface while carbon completely disappears after the second etching step. The existence of an Au-Ga alloy was detected and XPS spectra show only metal Ni and Ge within the layer and at the interface. We tried to perform a study about the depth chemical composition profile analysis of AuGeNi layer on cleaved n-GaAs(110) by X-Ray Photoelectron Spectroscopy (XPS) technique.

39. Microwave dielectric properties of BNT-BT0.08 thin films prepared by sol-gel technique

Authors: Huitema, L; Cernea, M; Crunteanu, A; Trupina, L; Nedelcu, L; Banciu, MG; Ghalem, A; Rammal, M; Madrangeas, V; Passerieux, D; Dutheil, P; Dumas-Bouchiat, F; Marchet, P; Champeaux, C

Published: APR 14 2016, JOURNAL OF APPLIED PHYSICS, 119, DOI: 10.1063/1.4945822

We report for the first time the microwave characterization of 0.92(Bi0.5Na0.5)TiO(3-)0.08BaTiO(3) (BNT-BT0.08) ferroelectric thin films fabricated by the sol-gel method and integrated in both planar and out-of-plane tunable capacitors for agile high-frequency applications and particularly on the WiFi frequency band from 2.4 GHz to 2.49 GHz. The permittivity and loss tangent of the realized BNT-BT0.08 layers have been first measured by a resonant cavity method working at 12.5 GHz. Then, we integrated the ferroelectric material in planar inter-digitated capacitors (IDC) and in out-of-plane metal-insulator-metal (MIM) devices and investigated their specific properties (dielectric tunability and losses) on the whole 100 MHz-15 GHz frequency domain. The 3D finite-elements electromagnetic simulations of the IDC capacitances are fitting very well with their measured responses and confirm the dielectric properties determined with the cavity method. While IDCs are not exhibiting an optimal tunability, the MIM capacitor devices with optimized Ir/MgO(100) bottom electrodes demonstrate a high dielectric tunability, of 30% at 2.45 GHz under applied voltages as low as 10 V, and it is reaching 50% under 20V voltage bias at the same frequency. These high-frequency properties of the MIM devices integrating the BNT-BT0.08 films, combining a high tunability under low applied voltages indicate a wide integration potential for tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used industrial, scientific, and medical frequency band. (C) 2016 AIP Publishing LLC.

40. Characteristics of Ce3+-doped barium titanate nanoshell tubes prepared by template-mediated colloidal chemistry

Authors: Ianculescu, AC; Vasilescu, CA; Trupina, L; Vasile, BS; Trusca, R; Cernea, M; Pintilie, L; Nicoara, A

Published: JUN 2016, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 36, 1642, DOI: 10.1016/j.jeurceramsoc.2016.01.045

5 mol% Ce3+-doped barium titanate nanoshell tubes were prepared via sol gel method using as template a polycarbonate membrane with channels of 200 nm diameter. FE-SEM analyses showed that continuous and uniform green tubes with length up to 15 mu m, an average outer diameter of 188.6 nm and wall thickness of 15.1 nm, were obtained. After calcination at 700 degrees C for 1 h, these amorphous 1D nanostructures were converted into polycrystalline tubes with an average outer diameter of 157.4 nm and a grain size of 43.4 nm, as high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) indicated. Thermo-Raman investigations pointed out diffuse phase transitions, inducing the preservation of a stable polar state at higher temperatures (up to 200 degrees C). Piezoresponse force microscopy (PFM) investigations on 5 mol% Ce3+-doped BaTiO3 nanoshell tubes revealed ferroelectric and piezoelectric behaviour which recommends these tubes for microelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved.

41. BST thin film capacitors integrated within a frequency tunable antenna

Authors: Rammal, M; Huitema, L; Crunteanu, A; Passerieux, D; Cros, D; Monediere, T; Madrangeas, V; Dutheil, P; Champeaux, C; Dumas-Bouchiat, F; Marchet, P; Nedelcu, L; Trupina, L; Banciu, G; Cernea, M

Published: 2016, 2016 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT), 47, DOI:

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

42. Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere

Authors: Trupina, L; Nedelcu, L; Negrila, C; Banciu, MG; Huitema, L; Crunteanu, A; Rammal, M; Ghalem, A

Published: SEP 2016, JOURNAL OF MATERIALS SCIENCE, 51, 8717, DOI: 10.1007/s10853-016-0131-1

The growth and thermal stability of textured iridium thin films used as bottom electrode in electronic devices based on ferroelectric materials were investigated. The thin films were grown using the dc magnetron sputtering technique. The Ir layers directly deposited on SiO2/Si substrates present a mixed (111) and (200) orientations, while the films grown on Ti seed layers exhibit a strong preferred (111) orientation favoured by good matching with the titanium lattice. The substrate temperature during the growth of iridium/titanium stack has a significant effect on the surface morphology of the iridium layer and its thermal stability. The as-grown surface of 20-nm-thick Ir films is smooth, having a root-mean-square (rms) roughness of 0.7 nm. After thermal annealing the Ir film shows an increased surface roughness due to the formation of agglomerations. The change in the surface morphology of the Ir layer is due to titanium diffusion and its oxidation. Thicker and better crystallised iridium thin films annealed in oxygen atmosphere at 700 A degrees C show a good thermal stability with only a slight modification of the surface morphology. Within the limits of experimental error, there is no change in the electrical resistivity before and after thermal annealing. The rms roughness has not varied significantly and the XPS investigation shows no traces of titanium oxide on iridium surface. Ir/Ti stack deposited under the optimum conditions could be successfully used as electrode in devices based on oxide thin films.

43. Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba2/3Sr1/3TiO3 thin films

Authors: Ghalem, A; Huitema, L; Crunteanu, A; Rammal, M; Trupina, L; Nedelcu, L; Banciu, MG; Dutheil, P; Constantinescu, C; Marchet, P; Dumas-Bouchiat, F; Champeaux, C

Published: NOV 14 2016, JOURNAL OF APPLIED PHYSICS, 120, DOI: 10.1063/1.4966942

We present the conduction mechanisms of Ba2/3Sr1/3TiO3 thin films integrated in metal-insulatormetal (MIM) capacitors and the modelling of the frequency-dependent electrostrictive resonances (in the 100 MHz-10 GHz domain) induced in the devices upon applying different voltage biases. Au/BST/Ir MIM structures on MgO substrates have been fabricated and, depending on their specific polarization, we highlighted different conduction mechanisms in the devices. Depending on the dc bias polarity, the conduction current across the material shows a space-charge-limited-current behavior under negative polarization, whereas under positive bias, the conduction obeys an electrode-limited Schottky-type law at the Au/BST interface. The application of an electric field on the device induces the onset of acoustic resonances related to electrostrictive phenomena in the ferroelectric material. We modeled these acoustic resonances over a wide frequency range, by using a modified Lakin model, which takes into account the dispersions of acoustic properties near the lower electrode/thin film interface. Published by AIP Publishing.

44. Comparison between the ferroelectric/electric properties of the PbZr0.52Ti0.48O3 films grown on Si (100) and on STO (100) substrates

Authors: Chirila, C; Boni, AG; Pasuk, I; Negrea, R; Trupina, L; Le Rhun, G; Yin, S; Vilquin, B; Pintilie, I; Pintilie, L

Published: JUN 2015, JOURNAL OF MATERIALS SCIENCE, 50, 3894, DOI: 10.1007/s10853-015-8907-2

Ferroelectric/electric properties of PbZr0.52Ti0.48O3 (PZT) thin films grown by pulsed laser deposition (PLD) on two different substrates, Si (001) and SrTiO3 (STO) (001), were comparatively analyzed. The structural characterization has revealed the epitaxial relationship between the grown layers and the two types of substrates, with larger density of structural defects for the films deposited on Si (001) with buffer STO layer. The ferroelectric/electric properties are also different, with lower remnant polarization (about half of the value obtained on STO substrate), higher dielectric constant (about two times larger), and lower leakage current (about two orders of magnitude lower) for the PZT films deposited on Si (001) compared to those deposited on (001) STO substrates. Nevertheless, the results show that the use of a STO buffer layer on Si can be a solution to obtain good quality PZT capacitor structures without using expensive single-crystal oxide substrates. In this way, applications based on PZT capacitors (e.g. non-volatile memories, pyroelectric detectors, light switches, etc.) would be more easily integrated directly on Si wafers.

45. Spectro-microscopic photoemission evidence of charge uncompensated areas in Pb(Zr,Ti)O-3(001) layers

Authors: Popescu, DG; Husanu, MA; Trupina, L; Hrib, L; Pintilie, L; Barinov, A; Lizzit, S; Lacovig, P; Teodorescu, CM

Published: 2015, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 520, DOI: 10.1039/c4cp04546g

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.

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

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

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

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

47. Electrode interface controlled electrical properties in epitaxial Pb(Zr0.52Ti0.48)O-3 films grown on Si substrates with SrTiO3 buffer layer

Authors: Boni, AG; Chirila, C; Pasuk, I; Negrea, R; Trupina, L; Le Rhun, G; Vilquin, B; Pintilie, I; Pintilie, L

Published: OCT 30 2015, THIN SOLID FILMS, 593, 130, DOI: 10.1016/j.tsf.2015.09.028

Electrical properties of ferroelectric capacitors based on PbZr0.52Ti0.48O3 thin films grown by pulsed laser deposition on silicon substrate with SrTiO3 buffer layer grown by molecular beam epitaxy were studied. A SrRuO3 layer was deposited as bottom electrode also by pulse laser deposition and Pt, Ir, Ru, SrRuO3 were used as top contacts. Electrical characterization comprised hysteresis and capacitance-voltage measurements in the temperature range from 150 K to 400 K. It was found that the macroscopic electrical properties are affected by the electrode interface, by the choice of the top electrode. However, even for metals with very different work functions (e.g. Pt and SrRuO3) the properties of the top and bottom electrode interfaces remain fairly symmetric suggesting a strong influence from the bound polarization charges located near the interface. (C) 2015 Elsevier B.V. All rights reserved.

48. Characteristics of 5 mol% Ce3+-doped barium titanate nanowires prepared by a combined route involving sol-gel chemistry and polycarbonate membrane-templated process

Authors: Vasilescu, CA; Trupina, L; Vasile, BS; Trusca, R; Cernea, M; Ianculescu, AC

Published: NOV 5 2015, JOURNAL OF NANOPARTICLE RESEARCH, 17, DOI: 10.1007/s11051-015-3241-9

Ba0.95Ce0.05Ti0.9875O3 nanowires were fabricated by sol-gel method using as template a polycarbonate membrane with channels of 100 nm diameter. FE-SEM analyses showed that continuous gel wires of length up to 17 mu m and an average diameter of 81 nm, were obtained. After calcination at 700 degrees C for 1 h, these green 1D nanostructures were converted into well-crystallised wires with an average diameter of 59.7 nm, as high-resolution transmission electron microscopy and selected area electron diffraction indicated. The piezoelectric activity of the Ba0.95Ce0.05Ti0.9875O3 nanowires was investigated using piezoresponse force microscopy (PFM) correlated with atomic force microscopy. The results of PFM measurements indicated that the wires exhibit a significant fraction of ferroelectric domains larger than the grains size and a good piezoelectric response.

49. Selective adsorption of contaminants on Pb(Zr,Ti)O-3 surfaces shown by X-ray photoelectron spectroscopy

Authors: Stoflea, LE; Apostol, NG; Trupina, L; Teodorescu, CM

Published: 2014, JOURNAL OF MATERIALS CHEMISTRY A, 2, 14392, DOI: 10.1039/c4ta02660h

X-ray photoelectron spectroscopy (XPS) analyses of lead zirco-titanate Pb(Zr,Ti)O-3(001) single crystal thin layers as a function of the time spent between sample preparation by pulsed laser deposition and introduction in to a ultrahigh vacuum revealed the fact that freshly prepared samples showed a shift of the C 1s towards a higher binding energy, together with shifts of core levels originating from the substrate (particularly Ti 2p and O 1s) towards a lower binding energy. This behaviour is explained by considering that the molecules of contaminants (fatty acids, alcohols, esters) are adsorbed preferentially on areas exhibiting outwards polarization P(+). Thus, photoelectrons originating from contaminants will have larger binding energies because of the charge state of the P(+) areas, whereas the substrate XPS signals from these P(+) areas are attenuated by the contaminants, with the consequence of a prevalence of XPS substrate signals originating from the P(-) areas, shifted towards lower binding energies. Piezoresponse force microscopy confirmed the assumptions derived from XPS results and suggests the existence of an interplay between the adsorption of contaminants and the surface polarization state.

50. Schottky barrier versus surface ferroelectric depolarization at Cu/Pb(Zr, Ti)O-3 interfaces

Authors: Stoflea, LE; Apostol, NG; Chirila, C; Trupina, L; Negrea, R; Pintilie, L; Teodorescu, CM

Published: MAY 2014, JOURNAL OF MATERIALS SCIENCE, 49, 3351, DOI: 10.1007/s10853-014-8041-6

The band bending at Cu/PZT(001) interfaces is investigated by X-ray photoelectron spectroscopy (XPS) for a PZT(001) layer which exhibits initial outwards ferroelectric polarization. Two competitive processes are identified: (a) formation of the Schottky barrier between the ferroelectric and unconnected Cu islands, and (b) coalescence of the Cu islands, realisation of an electrical contact to the ground of the system, inducing the apparent loss of the component of the ferroelectric polarization perpendicular to the sample surface, at least as it manifests in band bending. Three mechanisms are proposed to explain this loss of band bending when a full metal layer connected to ground is formed on the surface: (i) over-compensation of depolarization field in the sub-surface region, (ii) formation of domains with in-plane orientation of the polarization vector and (iii) loss of polarization in the near-surface layers of the ferroelectric due to electrons provided by the metal. These result in a non-monotonous variation of binding energies with the amount of Cu deposited. High resolution transmission electron microscopy and piezoresponse force microscopy confirmed these hypotheses. The XPS data allowed also to derive the surface PZT composition, its evolution with the deposition of copper and the formation of surface compounds.

51. BiFeO3 doped-BNT-BT0.08 piezoelectric and magnetic nanowires, derived from sol-gel precursor

Authors: Cernea, M; Trupina, L; Vasile, B; Bartha, C; Radu, R; Chirila, C; Teodorescu, A

Published: JAN 10 2014, JOURNAL OF NANOPARTICLE RESEARCH, 16, DOI: 10.1007/s11051-013-2231-z

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, doped with 5 mol %BiFeO3 (BNT-BT-BFO) nanowires was prepared from its corresponding precursor sol. A polycarbonate membrane with the thickness of 30 mu m and the pore diameter of 100 nm was used as template. Nanowires with average diameter of similar to 80 nm and different lengths of a few microns were prepared from BNT-BT-BFO precursor sol with similar to 0.03 M concentration. Ferroelectric and piezoelectric characterizations of BNT-BT-BFO nanowires were performed using AFM-PFM equipment. The HR-TEM micrograph of nanocrystals, SAED patterns, and XRD pattern indicated that BNT-BT-BFO nanowires crystallized on the lattice of rhombohedral (Na0.5Bi0.5TiO3) phase. The BNT-BT-BFO nanowires showed a significant piezoelectric response, suggesting a good piezoelectric behavior. The saturation magnetization of the nanowires, measured at room temperature and at 5 kOe magnetic field, was Ms = 0.061 emu/g. A saturated ferromagnetic hysteresis loop has been also obtained.

52. Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

Authors: Sandu, SG; Palade, P; Schinteie, G; Birsan, A; Trupina, L; Kuncser, V

Published: FEB 2014, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 181, 32, DOI: 10.1016/j.mseb.2013.11.004

In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(001) substrates by RF sputtering have been investigated using Fe-57 conversion electron Mossbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing. (C) 2013 Elsevier B.V. All rights reserved.

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

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

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

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

54. Nanotubes of piezoelectric BNT-BT0.08 obtained from sol-gel precursor

Authors: Cernea, M; Trupina, L; Vasile, BS; Trusca, R; Chirila, C

Published: JUL 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1787-y

Barium titanate-substituted bismuth titanate ((Bi0.5Na0.5)(0.92)Ba0.08TiO3, BNT-BT0.08) nanotubes were fabricated using sol-gel chemistry, spin casting, and a porous polycarbonate membrane template. The structure and morphology of the tubes have been investigated by scanning electron microscopy and transmission electron microscopy. The diameter and length of these tubes were about 650 nm and 20 mu m, respectively, and their wall thickness was about 50 nm. The tubes were polycrystalline with average grain size of similar to 40 nm. The BNT-BT0.08 nanotubes exhibited ferroelectric behavior as evidenced by saturated piezoresponse hysteresis loops and phase switching. BNT-BT0.08 piezoelectric nanotubes promise novel device architectures and enhanced electric properties.

55. BNT-BT0.08 wires derived from sol-gel precursor and their piezoelectric behavior

Authors: Cernea, M; Pintilie, L; Trupina, L; Vasile, BS; Chirila, C; Pasuk, I

Published: MAY 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1668-4

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, (abbreviated as BNT-BT0.08) wires were prepared using its corresponding precursor sol and, a polycarbonate template membrane. The polycarbonate membrane used has a thickness of 30 mu m and pore diameter of 300 nm. Uniform surface morphology of the wires with average diameter of 145 nm and a length of about 20 mu m was obtained when the concentration of the sol was 0.3 M. The ferroelectric and piezoelectric properties of an individual BNT-BT0.08 wire were investigated using the PFM technique. The hysteresis loops between the PFM phase and DC bias and, the characteristic butterfly loops of the PFM amplitude versus DC bias, indicated a ferroelectric and piezoelectric behavior of as-obtained BNT-BT0.08 wires.

56. Increased Diffusion Coefficient of Polymeric Nanocomposite Layer for Gas Sensing Applications

Authors: Nicolae, I; Viespe, C; Serban, N; Negrila, CC; Teodorescu, VS; Trupina, L

Published: DEC 2013, SENSOR LETTERS, 11, 2332, DOI: 10.1166/sl.2013.3083

A high-performance polymeric nanostructured sensing layer for a surface acoustic wave sensor, deposited using a modified matrix assisted pulsed laser evaporation direct write technique, exhibited improved performance in terms of response time and frequency deviation. In the present work, we assessed the factors and mechanisms that account for the layer's increased sensing capabilities. The increase in the sensing performance was attributed to an increased diffusion constant, due to greater molecular mobility of polymeric chains caused by the nanoparticles embedded in the polymer matrix.

57. A HIGH PERFORMANCE PIEZOCERAMIC MATERIAL FOR A VIBRATION TRANSDUCER FOR BALANCING OF ROTATING PARTS

Authors: Miclea, CT; Cioangher, M; Miclea, CF; Trupina, L; Miclea, C; Amarande, L; Spanulescu, S; Faibis, R

Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 294, DOI:

A high performance piezoceramic material of PZT type, doped with 6 atomic % W, was prepared in order to be used as sensing element for a vibration transducer used to equilibrate the motor-fan group of auto vehicles. The piezoelectric parameters of material showed high values which recommended it for the vibration transducer. The transducer consists of a ring shaped active element sandwiched between two steel blocks. The transducer works in quasistatic regime, at frequencies much lower than the resonance frequency, being tightly screwed in the measurement system by a metallic cover attached at the back end.

58. Pizeoelectric epitaxial sol-gel Pb(Zr0.52Ti0.48)O-3 film on Si(001)

Authors: Yin, S; Le Rhun, G; Defay, E; Vilquin, B; Niu, G; Robach, Y; Dragoi, C; Trupina, L; Pintilie, L

Published: 2012, 2012 INTERNATIONAL SYMPOSIUM ON APPLICATIONS OF FERROELECTRICS HELD JOINTLY WITH 11TH IEEE ECAPD AND IEEE PFM (ISAF/ECAPD/PFM), DOI:

Epitaxial Pb(Zr0.52Ti0.48)O-3 (PZT) thin film has been successfully integrated on Si(001) substrate by sol-gel method. SrTiO3 (STO) layer deposited on Si by Molecular Beam Epitaxy (MBE) acts as a template layer in this study to avoid the formation of amorphous SiO2, and allows the chemical compatibility for further epitaxial growth. For bottom electrode, SrRuO3 (SRO) layer grown by Pulsed Laser Deposition (PLD) on STO/Si was used. Epitaxial single crystalline growth of PZT film after Rapid Thermal Annealing (RTA) at 650 C was evidenced by X-Ray Diffraction (XRD). The following relationship in the heterostructure was deduced: [110] PZT (001) // [110] SRO (001) // [110] STO (001) // [100] Si (001). A clear piezoelectric response of the film was observed by Piezoresponse Force Microscope (PFM). Moreover, the structural STO quality was proved to have a major impact on the electrical properties of PZT films.

59. X-ray photoelectron spectroscopy of pulsed laser deposited Pb(Zr,Ti)O3-delta

Authors: Dragoi, C; Gheorghe, NG; Lungu, GA; Trupina, L; Ibanescu, AG; Teodorescu, CM

Published: JUN 2012, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 209, DOI: 10.1002/pssa.201127740

High quality pulsed laser deposited lead zirconate titanate (PZT) films are obtained by pulsed laser deposition on SrRuO3(111) single crystal layers and characterized by X-ray photoelectron spectroscopy (XPS), to determine the surface composition. It is found that a minor amount of Pb forms PbO2 at the surface and also some Pb is included into the contamination layer, in form of a Pb(CO3)2 layer of about 1?nm thickness, occupying about one quarter of the PZT surface. The stoichiometry of the outermost 45?nm layers yielded as PbZr0.25Ti0.80O2.5, which suggest the formation of an oxygen depleted, Brownmillerite-like layer at the surface, of at least 5?nm thickness.

60. Interface characterization and atomic intermixing processes in Be/W bilayers deposited on Si(001) substrates with Fe buffer layers

Authors: Kuncser, V; Palade, P; Schinteie, G; Sandu, SG; Trupina, L; Lungu, GA; Gheorghe, NG; Teodorescu, CM; Porosnicu, C; Jepu, I; Lungu, CP; Filoti, G

Published: JAN 25 2012, JOURNAL OF ALLOYS AND COMPOUNDS, 512, DOI: 10.1016/j.jallcom.2011.09.063

Structural aspects and atomic intermixing processes in Be/W bilayers deposited on Si(0 0 1) substrates with Fe buffer layers enriched in the (57)Fe Mossbauer isotope have been studied via atomic force microscopy, grazing incidence X-ray diffractometry, X-ray reflectometry, X-ray photoelectron spectroscopy and conversion electron Mossbauer spectroscopy. The mentioned investigations allowed a full sequential characterization of the involved interfaces. Various ionic configurations appeared for Fe or W, while an amorphous state was observed in the case of Be. It has been proven that the Be layer has a negative influence on the roughness of the whole structure, which however presents an oxidation gradient from more oxidized elements at the surface towards more reduced elements in deeper layers. A strong diffusion of the W atoms inside the Be layer, induced by the deposition method, as well as of the Fe atoms inside the Be layer, induced by thermal annealing, has been evidenced. (C) 2011 Elsevier B.V. All rights reserved.

61. Structural, optical, and electric properties of BNT-BT0.08 thin films processed by sol-gel technique

Authors: Cernea, M; Trupina, L; Dragoi, C; Galca, AC; Trinca, L

Published: OCT 2012, JOURNAL OF MATERIALS SCIENCE, 47, 6971, DOI: 10.1007/s10853-012-6646-1

Thin films with the composition [(Bi0.5Na0.5)TiO3](0.92)-[BaTiO3](0.08) (hereafter BNT-BT0.08) were deposited on Pt-Si by spin-coating from a stable sol precursor. The BNT-BT0.08 film, crystallized on the Bi0.5Na0.5TiO3 rhombohedral lattice, was obtained after annealing the film-gel at 700 A degrees C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT-BT0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (epsilon (r)) was 243 and the loss tangent (tan delta) was 0.38. The remnant polarization (P (r)) was 0.87 mu C/cm(2) and the coercive field (E (c)) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 x 10(-5) A/cm(2) at low electric fields (100 kV/cm). BNT-BT0.08 thin films shown piezoelectric properties (d (33eff) = 100 pm/V) comparable to those of PZT thin films.

62. Structural and piezoelectric characteristics of BNT-BT0.05 thin films processed by sol-gel technique

Authors: Cernea, M; Trupina, L; Dragoi, C; Vasile, BS; Trusca, R

Published: FEB 25 2012, JOURNAL OF ALLOYS AND COMPOUNDS, 515, 170, DOI: 10.1016/j.jallcom.2011.11.129

Polycrystalline ferroelectric lead-free (Bi0.5Na0.5)(0.95)Ba0.05TiO3 (BNT-NT0.05) thin films have been deposited on Pt/TiO2/SiO2/Si substrates by an optimized sol-gel/spin-coating process. The film thermal treated at 700 degrees C is dense and well crystallized in the rhombohedral perovskite phase. The film is composed of polyhedral shaped primary particles with an average size of approximately 35 nm, and has a smooth surface of 4.52 nm root mean square roughness (RMS). The nanoscale electrical properties of the film were investigated by piezoforce microscopy (PFM). The PFM data showed that most of the grains seem to be constituted of ferroelectric multiple domains. The maximum dielectric constant measured at zero bias voltage is about 210 and the leakage current density has a value of about 3 x 10(-5) A/cm(2) at an applied voltage about 8 V. These results indicate that, the BNT-NT0.05 thin film is a promising functional lead-free ferroelectric material. (C) 2011 Elsevier B. V. All rights reserved.

63. Catalyst size limitation in vapor-liquid-solid ZnO nanowire growth using pulsed laser deposition

Authors: Marcu, A; Trupina, L; Zamani, R; Arbiol, J; Grigoriu, C; Morante, JR

Published: MAY 1 2012, THIN SOLID FILMS, 520, 4631, DOI: 10.1016/j.tsf.2011.10.126

Using a pulsed laser deposition system in a plane reflector configuration, we have grown single crystal ZnO nanowires using different gold catalyst quantities and different local particle fluxes. The number of ZnO nanowire over the square micrometer substrate surface proved to depend on both gold quantity and particle flux, in specific conditions. If for a "low particle flux" the nanowire density seems to strongly depend on the gold quantity, for a "high particle flux", the dependence is no longer observable. The results were interpreted in terms of the catalyst absorbed particle concentration dependence on the catalyst droplet size and incident particle flux. (C) 2011 Elsevier B.V. All rights reserved.

64. EFFECT OF TEMPERATURE ON THE MAGNETIC PROPERTIES OF CERAMIC MAGNETIC MATERIALS USED FOR TEMPERATURE TRANSDUCERS

Authors: Miclea, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; Plavitu, C; Spanulescu, I; Mihailescu, M

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 272, DOI:

Three ceramic magnetic compositions within the CuZnTi ferrite system, having the Curie temperatures centered around 60 degrees C, 80 degrees C and 100 degrees C, respectively were investigated in order to determine the time-temperature stability of their main magnetic properties. Rates of changes of 33, 66 and 100 ppm/h of the maximum slopes of permeability were found for the samples aged at 60 degrees C, 80 degrees C and 100 degrees C, respectively. The samples aged at temperatures higher than 200 degrees C show a rather sudden decrease of the maximum slope of permeability, but no shift of the Curie temperature and the working point, corresponding to the temperature where the slope has the maximum value. The results are discussed in terms of the migration processes of the cations, especially Cu2+, from metastable positions on which they were frozen during the rapid cooling of the samples from the sintering temperature, to the more stable ones, namely the octahedral sites into the spinel lattice.

65. The study of the electric and magnetic properties of PbZr0.2Ti0.8O3-BiFeO3 multilayers

Authors: Stancu, V; Dragoi, C; Kuncser, V; Schinteie, G; Trupina, L; Vasile, E; Pintilie, L

Published: JUL 29 2011, THIN SOLID FILMS, 519, 6277, DOI: 10.1016/j.tsf.2011.03.136

The results of the electric and magnetic measurements performed on PbZr0.2Ti0.8O3-BiFeO3 symmetric structures, deposited on Pt/Si wafers, were compared for different number of layers in order to analyse the effect of interfaces over the macroscopic properties. It was found that the shape and magnitude of the capacitance-voltage characteristic, as well as the shape and parameters of the ferroelectric and magnetic hysteresis, depend on the number of interfaces in the intended multilayer structure. A temperature induced gradual transition from a magnetically disordered spin glass like phase of low temperature to an uncompensated antiferromagnetic phase at room temperature takes place in the BiFeO3 films, under low applied magnetic fields. A partial ferromagnetic like order can be obtained at low temperatures by increasing the field. The observed changes in the electric and magnetic behaviour of the systems were related to an increased degree of disorder for electric dipoles and magnetic moments, due to the increased number of layers and crystallization treatments. (C) 2011 Elsevier B.V. All rights reserved.

66. Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O-3 films obtained by pulsed laser deposition

Authors: Galca, AC; Stancu, V; Husanu, MA; Dragoi, C; Gheorghe, NG; Trupina, L; Enculescu, M; Vasile, E

Published: MAR 1 2011, APPLIED SURFACE SCIENCE, 257, 5943, DOI: 10.1016/j.apsusc.2011.01.056

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance. (C) 2011 Elsevier B.V. All rights reserved.

67. Lead-free ferroelectric BaTiO3 doped-(Na0.5Bi0.5)TiO3 thin films processed by pulsed laser deposition technique

Authors: Dragoi, C; Cernea, M; Trupina, L

Published: SEP 1 2011, APPLIED SURFACE SCIENCE, 257, 9605, DOI: 10.1016/j.apsusc.2011.06.075

The difficulties in synthesizing phase pure BaTiO3 doped-(Na0.5Bi0.5)TiO3 are known. In this work, we reporting the optimized pulsed laser deposition (PLD) conditions for obtaining pure phase 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO(3), (BNT-BT0.08), thin films. Dielectric, ferroelectric and piezoelectric properties of BNT-BT0.08, thin films deposited by PLD on Pt/TiO2/SiO2/Si substrates are investigated in this paper. Perovskite structure of BNT-BT0.08 thin films with random orientation of nanocrystallites has been obtained by deposition at 600 degrees C. The relative dielectric constant and loss tangent at 100 kHz, of BNT-BT0.08 thin film with 530 nm thickness, were 820 and 0.13, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 22 mu C/cm(2) and a coercive field of 120 kV/cm. The piezoresponse force microscopy (PFM) data showed that most of the grains seem to be constituted of single ferroelectric domain. The as-deposited BNT-BT0.08 thin film is ferroelectric at the nanoscale level and piezoelectric. (C) 2011 Elsevier B.V. All rights reserved.

68. Growth of highly oriented iridium oxide bottom electrode for Pb(Zr,Ti)O-3 thin films using titanium oxide seed layer

Authors: Trupina, L; Miclea, C; Amarande, L; Cioangher, M

Published: NOV 2011, JOURNAL OF MATERIALS SCIENCE, 46, 6834, DOI: 10.1007/s10853-011-5642-1

Due to its low resistivity and excellent thermal stability, IrO2 has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. Oriented growth of IrO2 electrode film was investigated with the goal to control the texture of the PZT thin film. IrO2 films were prepared by DC reactive sputtering. PZT film was prepared by RF magnetron sputtering single target deposition method. The whole layer stack was grown onto amorphous thermal oxide of a silicon wafer. The results indicate that IrO2 thin film was preferentially (200) oriented when a TiO2 seeding layer was used. The orientation relationships along the whole PZT(111)/IrO2(200)/TiO2(200)/Ti structure was discussed.

69. BEHAVIOR OF THE MAIN PROPETIES OF HARD AND SOFT TYPE PIEZOCERAMICS WITH TEMPERATURE FROM 2 TO 600 K

Authors: Miclea, C; Tanasoiu, T; Miclea, CF; Amarande, L; Cioangher, M; Trupina, L; Iuga, A; Spanulescu, I; Miclea, CT; David, C; Susu, M

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 304, DOI:

The application area of piezoceramic materials and devices based on such materials is continuously extended. The working conditions for such devices and structures may be sometimes very hard such as low and high temperatures, nuclear radiation, high pressure and so on. Such conditions may affect to some extent the transducer performances due to the changes of the basic properties of piezoceramic materials used as sensors. In this regard we have investigated the changes of the main piezoelectric properties of two typically hard and soft piezoceramics within a large temperature range from 2 to 600 K. All parameters measured showed a rather steady increase or decrease with increasing temperature. The results were discussed in terms of intrinsic and domain wall contribution to the dielectric and piezoelectric response of materials.

70. Magnetoelectric properties of multiferroic cobalt ferrite and soft piezoelectric PZT particulate composites

Authors: Miclea, C; Tanasoiu, C; Amarande, L; Miclea, CF; Plavitu, C; Cioangher, M; Trupina, L; Miclea, CT; Tanasoiu, T; Susu, M; Voicu, I; Malczanek, V; Ivanov, A; David, C

Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 276, DOI:

Multiferroic composite materials, consisting of piezoelectric and piezomagnetic phases, show electric polarization in the presence of a magnetic field and magnetization on applying an electric field, i.e. piezomagnetic phase causes polarization while piezoelectric phase causes changes in magnetization. The figure of merit of such multiferroic particulate composites is the magnetoelectric voltage coefficient representing the amount of polarization induced by a given magnetic field. In the present investigation we prepared and studied the properties of bulk particulate composites made from cobalt ferrite (COF) and a soft piezoelectric material (PZT). Composite samples, according to the formula xCOF center dot(1-x)PZT with 0 <= x <= 1 were prepared by mixing the COF and PZT powders, pressing them as discs and then sintered at 1200 degrees C for 3 hours. Structural, magnetic, piezoelectric and magnetoelectric characteristics of the sintered composites were determined as a function of the mass fraction of COF into PZT and magnetic field. The ME coefficient shows a maximum value of about 70 mV/cm.Oe for composites containing 40 % COF and 60 % PZT, in a DC magnetic field of 3 kOe at a frequency of 1 KHz of the ac magnetic field. Some of the dielectric and piezoelectric properties of the composite samples, as a function of the mass fraction x, were also determined.

71. Soft type PZT material used to fabricate a high intensity air siren

Authors: Miclea, C; Iuga, A; Tanasoiu, C; Trupina, L; Cioangher, M; Miclea, CT; Malczanek, V; Susu, M; Voicu, I

Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 281, DOI:

A high quality soft type PZT material was designed and produced in order to be used as sensor for a high intensity air siren, Two thin disks from this material were assembled into a parallel bimorph type sensor with an intermediate metallic plate for the siren. This assembly behaves like an acoustic resonator in the high frequency audio range. This structure transforms the radial mode of vibration into a flexural one, with a much lower frequency. A mechanical impedance adapter was used in order to assure a good match between the oscillating ceramic and the surrounding air. A theoretical approach was outlined, which allows the evaluation of the resonance frequency for the working transducer. The theoretical and experimental data agree to a satisfactory degree up to the input errors assumed by the model. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. The bimorph necessary for making the siren was designed as a parallel structure and the corresponding transducer was measured and evaluated. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

72. Ferroelectric Schottky diode behavior from a SrRuO3-Pb(Zr0.2Ti0.8)O-3-Ta structure

Authors: Pintilie, L; Stancu, V; Trupina, L; Pintilie, I

Published: AUG 18 2010, PHYSICAL REVIEW B, 82, DOI: 10.1103/PhysRevB.82.085319

A single ferroelectric Schottky diode was obtained on a SrRuO3-Pb(Zr0.2Ti0.8)O-3-Ta (SRO-PZT20/80-Ta) structure in which the SRO-PZT20/80 interface is the rectifying contact and the PZT20/80-Ta interface behaves as a quasiohmic contact. Both the capacitance-voltage (C-V) and the current-voltage (I-V) characteristics show the memory effect due to the ferroelectric polarization. However, retention studies had revealed that only the "down" orientation of ferroelectric polarization is stable in time (polarization oriented from top to bottom contact). The analysis of the experimental results suggests that the PZT20/80 is n type and that the stable orientation of polarization is related to the presence of a depletion region at the SRO-PZT20/80 Schottky interface.

73. Structure and properties of (Cu Ca Bi) doped KNN lead-free piezoceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Trupina, L; Cioangher, M; Miclea, CT; Malczanek, V; Susu, M; Voicu, I; Ivanov, A

Published: SEP 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 946, DOI:

Lead free ceramics in the system (1-x)KNN x(Bi2O3,CaO,CuO) with 0.0 <= x <= 0.1 were synthesized by the usual solid state reaction and their structural and piezoelectric properties were investigated Dense samples with densities of about 4 68 g/cm(3) were prepared by sintering at an optimum temperature of 1150 degrees C for 6 h Only perovskite phase was detected by X-ray investigation in all samples A typical MPB where orthorombic-tetragonal phases coexist was detected for a doping level of 0.06 where the piezoelectric parameters showed maximum values Planar coupling factor, as much as 0.46, piezoelectric charge constant of 270 pC/N and mechanical quality factor Q(m) of 75 were recorded for the samples situated within the MPB.

74. Effect of Nickel-Niobium Co-Doping on Structural, Electromechanical, and Dielectric Properties of Lead Titanate Ceramics

Authors: Amarande, L; Miclea, C; Tanasoiu, T; Iuga, A; Cioangher, MC; Trupina, L; Grecu, MN; Pasuk, I

Published: SEP 2009, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, 56, 1798, DOI: 10.1109/TUFFC.2009.1251

Lead titanate (PT) ceramics co-doped with 8 to 13 mol% Ni-Nb, by substituting titanium ions, were prepared by conventional ceramic method and the influence of Ni-Nb doping level on their mopho-structural, electromechanical and dielectric properties was investigated. Dense tetragonal PT ceramics were obtained for 8 to 12 mol% Ni-Nb co-doping. Lattice anisotropy decreased from 1.053 to 1.046 with increasing doping level. Large thickness coupling factors of 0.4 were obtained for 8, 11, and 12 mol% Ni-Nb. Large electromechanical anisotropy of 10 was obtained for 8 mol% Ni-Nb. It was found that Ni-Nb co-doping has both softening and hardening effects as a function of donor or acceptor behavior of different amounts of Ni-Nb. For 13 mol% Ni-Nb, segregation of a small amount of a secondary phase occurs, lattice constants and tetragonality significantly decrease and the resulting ceramic becomes very hard.

75. Evolution of the surface morphology with temperature, in oxidant atmosphere, of Ba (Ti1-xSnx)O-3 (x=0.13) thin films

Authors: Cernea, M; Trupina, L; Plapcianu, C; Trusca, R; Galassi, C

Published: SEP 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 950, DOI:

Thin films of Ba(Ti1-xSnx)O-3 with x = 0.13 have been deposited by rf-magnetron sputtering and their growth morphology and structure vs annealing temperature, in oxygen atmosphere, have been investigated The films deposited on silicon-platinum substrates, at room temperature, in Ar atmosphere were amorphous The as-obtained films had a mean surface roughness (RMS) around 6.529 nm and a grain size of about 150 nm By annealing the film up to 1150 degrees C in oxygen, the grains size increases up to 1-1.5 mu m in diameter Films containing BaTi0.87Sn0.13 as crystalline phase with the cubic structure of BaTiO3 and, bundle-like morphology were obtained by heating the film at 1250 degrees C for 3h in oxygen The as-obtained film showed the preferential (110) and (100) orientations

76. A PZT Based Material for Bimorph Type Transducers and a New Optical Method to Evaluate the Bimorph Performance

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Spanulescu, I; Plavitu, CN; Cioangher, M; Trupina, L; Miclea, CT; Susu, M

Published: 2008, ADVANCED MATERIALS FORUM IV, 587-588, +, DOI: 10.4028/www.scientific.net/MSF.587-588.253

The displacement devices using piezoceramic sensors play an important role in many fields. Soft type piezoelectric materials used for such sensors arc more appealing because of their lower coercive field, relatively low modulus of elasticity, high electromechanical coupling factors and piezoelectric strain coefficients. We designed a PZT type material doped with niobium and nickel to increase the strain coefficient and still retaining a high coupling coefficient. The chemical formula was Pb0.9Ba0.08Nb0.03Ni0.06Zr0.46Ti0.40O3. The main piezoelectric parameters were: d(33)=680 pm/V. d(31)=-235 pm/V, k(p)=0.64 and k(31)=0.42. A unimorph transducer was made from a thin sheet of such a piezoceramic material, tightly bonded on a thin optically polished glass plate and mounted as a cantilever. The performance of this transducer was evaluated by means of a new optical method which makes use of the Moire deflectometry and provides high precision. The method is rather simply and consists mainly in the following: the Moire fringes rotate when the bimorph bends under the influence of the electric field and by measuring the rotating angle of the fringes one can easily determine the bimorph curvature and the free end displacement.

77. Nanostructured PZT type thin films prepared by thermonic vacuum arc method

Authors: Rasleanu, D; Ionescu, V; Prodan, G; Ciupina, V; Lungu, CP; Surdu-Bob, C; Osiac, M; Pompilian, O; Badulescu, M; Lungu. AM; Ticos, C; Zaroschi, V; Trupina, L; Miclea, C

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3047, DOI:

PZT type films were prepared using the thermionic vacuum arc (TVA) method; a crucible filled PZT type powder (PbO/ZrO/TiO) was heated by a thermo-electron beam emitted by the circular cathode of the TVA gun. Applying high voltage potential (3000 +/- 200V) on the anode from a regulated HEINZINGER high voltage power supply the thermo-electrons were accelerated toward the anode crucible, evaporating the anode materials and initiating a plasma discharge. The morphology and the structure of the prepared films analyzed by transmission electron microscopy, (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy, showed nanostructured, smooth thin films with specific PZT stoichiometry.

78. A Study of the Changes Produced by Sintering on the Shape and Densification of Green Compacted Samples

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Plavitu, C; Cioangher, M; Trupina, L; Miclea, CT; David, C

Published: 2008, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 11, 107, DOI:

In order to determine the effect of sample shape, compacting pressure and green density gradients on the final shape and density of sintered bodies a study was made on a PZT type powder, pressed within a large range of shapes from long cylinders up to thin discs and at pressures ranging between 40 and 180 MPa. Important shape distorsion were found for both long cylinders and thin discs but surprisingly the final density was not essentially changed even if the green compacted density showed important changes with in the samples. Differences in the shrink age of diameter and thickness brought about by sintering for samples with different shapes were found.

79. A HIGH PERFORMANCE PZT TYPE MATERIAL USED AS SENSOR FOR AN AUDIO HIGH FREQUENCY PIEZOELECTRIC SIREN

Authors: Miclea, C; Tanasoiu, C; Iuga, A; Spanulescu, I; Miclea, CF; Plavitu, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; Tanasoiu, T

Published: 2008, CAS: 2008 INTERNATIONAL SEMICONDUCTOR CONFERENCE, PROCEEDINGS, +, DOI: 10.1109/SMICND.2008.4703364

A high quality PZT type material was designed and produced in order to be used as sensor for a high internsity siren. Two disks from this materials were assembled into a parallel bimorph type transducer with an intermediate metallic plate. This assembly behaves like an acoustic resonator in the high frequency audio range. The fundamental of the flexural mode for a free resonator is taken into account Its frequency dependence on the geometry of the system and on its material properties is computed using the results for a circular plate with clamped edges and an observation on the equivalence between the movement of a particular part of a resonator in a stationary state and the movement of that pari separated from the resonator but with the same border conditions. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

80. Temperature dependence of the main piezoelectric parameters of a Nb-Li doped PZT ceramic

Authors: Miclea, C; Tanasoiu, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; David, C

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

A study was made on the temperature behavior of the main piezoelectric parameters, namely the electromechanical coupling factor k(p), the mechanical quality factor Q, the dielectric permittivity (real and imaginary part), the loss tangent t(g) and the piezoelectric charge constants 6133 and d(31) of a soft type piezoelectric material. It was evidenced that temperatures under 150 degrees C do not influence these parameters, which means that every transducer made from this type of material may be successfully used up to this temperature. Between 150 degrees C and 250 degrees C, the piezoelectric properties undergo more or less important changes, mainly due to the depoling effect. After that, at temperatures over 250 degrees C, they degrade very rapidly, tending to zero.

81. Sintering behavior of hard-soft PZT-Type composite ceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Spanulescu, I; Trupina, L; Cioangher, M; Miclea, CT

Published: 2007, FERROELECTRICS, 351, 186, DOI: 10.1080/00150190701354265

Functionally graded materials represent a new class of composite type materials characterized by a continuous variation of properties through the thickness direction. Due to this they found numerous applications in aerospace, automobile, biomedical or nuclear industries. Bilayered structures made from typically hard and typically soft PZT type materials as well as plain hard and soft and intimately mixed hard and soft samples were prepared by green pressed powdersfollowed by sintering at different temperatures between 1000 and 1300 degrees C. The dielectric and piezoelectric properties of sintered compacts were determined in relation with the nature of the interdiffusion layer involved. Electron microscopy as well as X-Ray diffractometry was used to get an insight into the interfacial diffusion process. The composition and the width of the interdiffusion layer depend on temperature. The mechanism of the interdiffusion layer and materials properties were discussed in terms of the ionic diffusion coefficients and activation energies of the species which take place into the diffusion process.

82. Effect of temperature on the main piezoelectric parameters of a soft PZT ceramic

Authors: Miclea, C; Tanasoiu, C; Amarande, L; Miclea, CF; Plavitu, C; Cioangher, M; Trupina, L; Miclea, CT; David, C

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 250, DOI:

The temperature behavior of the main piezoelectric parameters, such as the electromechanical coupling factor k(p), the mechanical quality factor Qm, the dielectric permittivity epsilon (real and imaginary part), the loss tangent tan delta, the piezoelectric charge constants d(33) and d(31) and the voltage constants 933 and 931 of a soft type piezoelectric material was investigated. The results showed that temperatures under 150 degrees C do not influence these parameters, which indicate that every transducer made from this type of material may be successfully used up to this temperature. Between 150 degrees C and 250 degrees C, the piezoelectric properties undergo more or less important changes, mainly due to the depoling effect and above that, at temperatures over 250 degrees C, they degrade very rapidly, tending to zero.

83. Sintering distorsion produced by differences in green density and sample shape of PZT compacted powders

Authors: Miclea, C; Tanasoiu, C; Spanulescu, I; Miclea, CF; Gheorghiu, A; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; David, C

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

A study was made to determine the effect of sample shape, compacting pressure and green density gradients on the final shape and density of sintered bodies. Experiments were carried out on a PZT type powder, pressed with a large range of shapes from long cylinders up to thin discs, at pressures ranging between 40 and 180 MPa. Important shape distorsion were found for both long cylinders and thin discs but surprisingly the final density was not essentially changed even if the green compacted density showed important changes within the samples. Differences in shrinkage of diameter and thickness brought about by sintering for samples with different shapes were found.

84. Effect of lead content on the structure and piezoelectric properties of hard type lead titanate-zirconate ceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Gheorghiu, A; Spanulescu, I; Plavitu, C; Miclea, CT; Cioangher, MC; Trupina, L; Iuga, A

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 4059, DOI: 10.1016/J.jeurceramsoc.2007.02.094

In the present investigation we studied the effect of lead content on a hard type ceramics starting from lack to excess PbO. Specimens of Pb-x(Mn0.017Sb0.033Zr0.48Ti0.47)O-3 with 0.96 <= x <= 1.06 were prepared by conventional oxide mixing technique and sintered at temperatures between 1280 and 1350 degrees C. In samples with lower Ph concentration the pyrochlore phase appeared, while in those with higher Pb an excess of PbO phase was detected. These phases proved detrimental for the properties of sintered ceramics. The highest values of piezoelectric properties were observed only for samples with an excess lead of about 2% sintered at 1340 degrees C, indicating that it represents the optimum amount of PbO. For such samples, the density p was 7.77 g/cm (3). the remnant polarization P, was 37 mu C/cm(3) the planar coupling coefficient k(P) was 0.57 and the charge constant d(33) was 340 C-P/N. (c) 2007 Elsevier Ltd. All rights reserved.

85. Superconductor-ferroelectric heterostructures

Authors: Constantin, C; Ramer, R; Matei, I; Trupina, L; Stegarescu, M

Published: 1999, FERROELECTRICS, 225, 1092, DOI:

Superconductor-ferroelectric heterostructures were prepared by deposition of ferroelectric doped-PZT type material on the top of the superconductor YBCO thin films. Both, ferroelectric and superconductor thin films were obtained by off-axis RF magnetron sputtering method with a single target. On these heterostructures, measurements were made in order to evidence the influence of contact between the two materials on the electrical and thermal parameters. X-ray diffraction patterns of superconductor thin film show a good crystallization c-axis oriented perpendicular to the substrate plane, and a perovskite structure without traces of pyrochlore at 550 degrees C the ferroelectric thin film deposited by RF magnetron sputtering (off axis method). Important variations of the critical temperature of superconductor films have been obtained, due to the increased dielectric permittivity (epsilon).

Dr. Lucian TRUPINA

Scientific Researcher III

Resume

Projects

1. Integration of new and improved materials for smart millimeter-wave sensors

Publications

1. Atomically Thin MoS2 Layers Selectively Grown on Mo Patterned Substrates for Field-Effect-Controlled Photosensors

2. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films

3. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

4. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

5. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O3 Thin Films

6. Experimental Band Structure of Pb(Zr,Ti)O3: Mechanism of Ferroelectric Stabilization

7. Surface charge dynamics on air-exposed ferroelectric Pb(Zr,Ti)O3(001) thin films

8. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films

9. Pulsed laser deposited V2O3 thin-films on graphene/aluminum foil for micro-battery applications

10. Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O-3 films through Nb (n-type) and Fe (p-type) doping

11. Magnetic Properties of Nanosized Fe and FeCo Systems on Trenched Mo Templates

12. Accidental Impurities in Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films Grown by Pulsed Laser Deposition and Their Impact on the Macroscopic Electric Properties

13. Effect of strain and stoichiometry on the ferroelectric and pyroelectric properties of the epitaxial Pb(Zr0.2Ti0.8)O-3 films deposited on Si wafers

14. Homogeneous versus Inhomogeneous Polarization Switching in PZT Thin Films: Impact of the Structural Quality and Correlation to the Negative Capacitance Effect

15. Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

16. Electro-active properties of nanostructured films of cytosine and guanine nucleobases

17. CO adsorption, reduction and oxidation on Pb(Zr,Ti)O-3(001) surfaces associated with negatively charged gold nanoparticles

18. Investigation of Ba0.6Sr0.4TiO3 thick films by means of a novel THz-TDS approach

19. Unexpected magneto-functionalities of amorphous Fe-Gd thin films crossing the magnetization compensation point

20. Polarization Switching and Negative Capacitance in Epitaxial PbZr0.2Ti0.8O3 Thin Films

21. Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

22. Polarization-dependent magnetism of the Ni/BaTiO3 interface

23. Room temperature ferromagnetism and its correlation to ferroelectricity of manganese embedded in lead zirco-titanate

24. Frequency selective surfaces with hexagonal elements for millimeter waves applications

25. EXPERIMENTAL STUDY OF TERAHERTZ RESPONSE FROM SOME FERROELECTRIC AND DIELECTRIC MATERIALS

26. Memcomputing and Nondestructive Reading in Functional Ferroelectric Heterostructures

27. Structural, electric and pyroelectric properties of up and down graded PZT multilayers

28. Triggering surface ferroelectric order in Pb(Zr, Ti)O-3(001) by deposition of platinum

29. Polarization Orientation in Lead Zirconate Titanate (001) Thin Films Driven by the Interface with the Substrate

30. Millimeter wave and Terahertz investigations on some dielectric materials

31. Enhanced near-infrared response of a silicon solar cell by using an up-conversion phosphor film of Yb/Er - co-doped CeO2

32. Microwave antenna array using new dielectric resonator antenna elements

33. Low-energy electron diffraction from ferroelectric surfaces: Dead layers and surface dipoles in clean Pb(Zr, Ti)O-3(001)

34. Polarization landscape effects in soft X-ray-induced surface chemical decomposition of lead zirco-titanate, evidenced by photoelectron spectromicroscopy

35. Relation between domain structure and pyroelectric response in as-grown epitaxial Pb(Zr0.2Ti0.8)O-3 thin films on substrates with different resistivity

36. Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces

37. Ultra-High Tunability of Ba(2/3)Sr(1/3) TiO3-Based Capacitors Under Low Electric Fields

38. XPS Analysis of AuGeNi/Cleaved GaAs(110) Interface

39. Microwave dielectric properties of BNT-BT0.08 thin films prepared by sol-gel technique

40. Characteristics of Ce3+-doped barium titanate nanoshell tubes prepared by template-mediated colloidal chemistry

41. BST thin film capacitors integrated within a frequency tunable antenna

42. Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere

43. Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba2/3Sr1/3TiO3 thin films

44. Comparison between the ferroelectric/electric properties of the PbZr0.52Ti0.48O3 films grown on Si (100) and on STO (100) substrates

45. Spectro-microscopic photoemission evidence of charge uncompensated areas in Pb(Zr,Ti)O-3(001) layers

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

47. Electrode interface controlled electrical properties in epitaxial Pb(Zr0.52Ti0.48)O-3 films grown on Si substrates with SrTiO3 buffer layer

48. Characteristics of 5 mol% Ce3+-doped barium titanate nanowires prepared by a combined route involving sol-gel chemistry and polycarbonate membrane-templated process

49. Selective adsorption of contaminants on Pb(Zr,Ti)O-3 surfaces shown by X-ray photoelectron spectroscopy

50. Schottky barrier versus surface ferroelectric depolarization at Cu/Pb(Zr, Ti)O-3 interfaces

51. BiFeO3 doped-BNT-BT0.08 piezoelectric and magnetic nanowires, derived from sol-gel precursor

52. Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

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

54. Nanotubes of piezoelectric BNT-BT0.08 obtained from sol-gel precursor

55. BNT-BT0.08 wires derived from sol-gel precursor and their piezoelectric behavior

56. Increased Diffusion Coefficient of Polymeric Nanocomposite Layer for Gas Sensing Applications

57. A HIGH PERFORMANCE PIEZOCERAMIC MATERIAL FOR A VIBRATION TRANSDUCER FOR BALANCING OF ROTATING PARTS

58. Pizeoelectric epitaxial sol-gel Pb(Zr0.52Ti0.48)O-3 film on Si(001)

59. X-ray photoelectron spectroscopy of pulsed laser deposited Pb(Zr,Ti)O3-delta

60. Interface characterization and atomic intermixing processes in Be/W bilayers deposited on Si(001) substrates with Fe buffer layers

61. Structural, optical, and electric properties of BNT-BT0.08 thin films processed by sol-gel technique

62. Structural and piezoelectric characteristics of BNT-BT0.05 thin films processed by sol-gel technique

63. Catalyst size limitation in vapor-liquid-solid ZnO nanowire growth using pulsed laser deposition

64. EFFECT OF TEMPERATURE ON THE MAGNETIC PROPERTIES OF CERAMIC MAGNETIC MATERIALS USED FOR TEMPERATURE TRANSDUCERS

65. The study of the electric and magnetic properties of PbZr0.2Ti0.8O3-BiFeO3 multilayers

66. Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O-3 films obtained by pulsed laser deposition

67. Lead-free ferroelectric BaTiO3 doped-(Na0.5Bi0.5)TiO3 thin films processed by pulsed laser deposition technique

68. Growth of highly oriented iridium oxide bottom electrode for Pb(Zr,Ti)O-3 thin films using titanium oxide seed layer

69. BEHAVIOR OF THE MAIN PROPETIES OF HARD AND SOFT TYPE PIEZOCERAMICS WITH TEMPERATURE FROM 2 TO 600 K

70. Magnetoelectric properties of multiferroic cobalt ferrite and soft piezoelectric PZT particulate composites

71. Soft type PZT material used to fabricate a high intensity air siren

72. Ferroelectric Schottky diode behavior from a SrRuO3-Pb(Zr0.2Ti0.8)O-3-Ta structure

73. Structure and properties of (Cu Ca Bi) doped KNN lead-free piezoceramics

74. Effect of Nickel-Niobium Co-Doping on Structural, Electromechanical, and Dielectric Properties of Lead Titanate Ceramics

1. Atomically Thin MoS₂ Layers Selectively Grown on Mo Patterned Substrates for Field-Effect-Controlled Photosensors

5. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr_0.2Ti_0.8)O₃ Thin Films

6. Experimental Band Structure of Pb(Zr,Ti)O₃: Mechanism of Ferroelectric Stabilization

7. Surface charge dynamics on air-exposed ferroelectric Pb(Zr,Ti)O₃(001) thin films