Publications

The short-circuit photocurrent was measured in ferroelectric capacitors of polycrystalline and epitaxial quality. The interest was to study the possible relation between photocurrent and back-switching phenomena due to ferroelectric polarization imprint, as suggested by Pintilie [J. Appl. Phys. 101, 064109 (2007)]. An interesting relation between the shape of the ferroelectric hysteresis loop and the shape of the photocurrent spectral distribution was found. In polycrystalline samples, the shape of spectral distribution and the sign of photocurrent are changing in time, although the hysteresis is almost symmetrical. However, the hysteresis is not rectangular as in the case of epitaxial films. This behavior suggests a subtle relation between polarization back-switching and photocurrent. In epitaxial samples a peculiar dependence between photocurrent and polarization imprint was found. All these are explained assuming the presence of an internal field, possibly generated by charged defects, which can change its direction and magnitude under illumination, with consequence on the orientation and magnitude of the ferroelectric polarization, and on the sign/shape of the short-circuit photocurrent spectral distribution. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3445877]

The implants surfaces investigated in the present study were modified with the films of poly (vinyl) alcohol (PVA) which were formed in physiological serum (0.9% NaCl). Surfaces evaluation included electrochemical measurements such as linear potentiometry (LP) and electrochemical impedance spectroscopy (EIS). These suggest that PVA acts by adsorption at site on the metal surface and formed a compact, adherent and uniform layer. The composition of layer was estimated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/ EDX) and X-ray Photoelectron Spectroscopy (XPS) techniques, which confirm the adsorption of PVA on the surfaces, through -OH groups, with a specific affinity to the titanium sub-strate.

We report here on the nitrogen doped ZnO (ZnO:N) thin films deposited by radio frequency (rf) magnetron sputtering using ZnN target (99.9% purity) on, unintentionally heated, fused silica substrates. After deposition Rapid Thermal Annealing (RTA) at 400 and 550 degrees C for 1min in N-2 ambient have been performed on the ZnO:N thin films. The RTA impact on the optical and microstructural properties of ZnO:N thin films have been investigated by X-ray diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy coupled with Energy Dispersive X-ray analysis, UV-VIS-NIR spectrophotonnetry and UV-VIS-NIR-Far IR Spectroscopic Ellipsometry. XRD and AFM results revealed an improvement in the crystalline state of ZnO:N and a reduction in the films surface roughness following RTA. The EDX spectrum showed the presence of the nitrogen in small quantities in the ZnO structure (nitrogen/oxygen=1/8). The optical constants of ZnO:N from UV down to Far IR spectral range together with the infrared active modes for ZnO:N are also reported.

Exchange bias AF/Fe and spin valve AF/Fe/Cu/Fe (AF=Fe50Mn50 and Ir50Mn50) multilayer systems have been prepared by molecular beam epitaxy. Thin tracer layers enriched in the Fe-57 isotope were artificially grown at the AF/Fe interface and the phase composition of the ferromagnetic layer, as well as the interfacial atomic diffusion were observed via Fe-57 conversion electron Mossbauer spectroscopy. The dependence of the magnetization reversal process on training and temperature associated effects was studied by low temperature vibrating sample magnetometry, whereas the interlayer magnetic coupling was analyzed via longitudinal magneto-optic Kerr effect.

In order to study the influence of the cations substitution on permeability of cobalt ferrites four series of samples with different chemical composition were prepared by conventional ceramic method. The calcined powders and sintered samples were characterized by X-ray diffraction and vibrating samples magnetometer. The microstructure of the samples was analyzed by surface electron microscopy. The initial permeability spectra at room temperature were plotted using the torus standard method. Chemical composition and the microstructure influence the magnetic properties and the initial permeability spectra of the cobalt ferrites samples. Small amount of manganese ions decreases the Curie temperature, increase the initial permeability and saturation magnetization and decreases the coercive magnetic field, thus improving the performances of cobalt ferrites for magnetostrictive sensors applications.

Holmium-doped BaTiO3 with composition Ba0.97Ho0.03TiO3 was prepared by sol-gel combustion method. A molar ratio of citrate/nitrate (CA/NO3- = 1.3) was used to prepare nanopowders of (Ba,Ho)TiO3. The structure and microstructure of (Ba,Ho)TiO3 powders and ceramics were investigated. The ceramics exhibit a dielectric constant of about 4400 and dielectric loss (tan delta = 0.267) at 10 Hz, and at the Curie temperature (T-c = 132 degrees C). The remanent polarization and the coercive field of Ba0.97Ho0.03TiO3 ceramics, at 1 kHz, were P-r = 6 mu C/cm(2) and E-C = 0.75 kV/cm. The dielectric and ferroelectric behavior of the holmium-doped BaTiO3 is influenced by the amphoteric character of Ho3+ ions.

A short description of approaches for carbon nanostructures synthesis is made and the advantages of using plasma during the growth are presented. As a particular example of a plasma based technique we detail the process of downstream carbon nanowall (CNW) synthesis by a radiofrequency expanding plasma beam. The technique combines magnetron sputtering for catalyst deposition and plasma enhanced chemical vapor deposition (main gas: argon, active gas: hydrogen, precursor gas: acetylene) for carbon growth in a single reactor. The analysis focuses on the correlation between the material properties and the plasma characteristics measured at different points along the flow axis, aiming to reveal the importance of plasma species in the growth process. The material properties were investigated by scanning and transmission electron microscopy, whereas the plasma data were obtained by optical emission spectroscopy, Langmuir probes and mass spectrometry. CNWs with a large area and well isolated from each other are obtained at an optimum distance from the precursor injection point where the plasma presents an enhanced content of carbon nanoclusters. The possible processes responsible for the growth are discussed.

Functionalized implants represent an advanced approaching in implantology, aiming to improve the biointegration and the long-term success of surgical procedures. We report on the synthesis of hydroxyapatite (HA) thin films on polymethylmetacrylate (PMMA) substrates - used as cranio-spinal implant-type structures - by two alternative methods: pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (MS). The deposition parameters were optimized in order to avoid the substrate overheating. Stoichiometric HA structures were obtained by PLD with incident laser fluences of 1.4-2.75 J/cm(2), pressures of 30-46.66 Pa and 10 Hz pulses repetition rate. The MS depositions were performed at constant pressure of 0.3 Pa in inert and reactive atmospheres. SEM-EDS, XRD, FTIR and pull-out measurements were performed assessing the apatitic-type structure of the prepared films along with their satisfactory mechanical adhesion. Cell viability, proliferation and adhesion tests in osteosarcoma SaOs2 cell cultures were performed to validate the bioactive behaviour of the structures and to select the most favourable deposition regimes. For PLD, this requires a low thence of 1.4 J/cm2, reduced pressure of water vapours and a 100 degrees C/4 h thermal treatment. For MS, the best results were obtained for 80% Ar + 20% O-2 reactive atmosphere at low RF power (similar to 75 W). Cells grown on these coatings exhibit behaviour similar to those grown on the standard borosilicate glass control: increased viability, good proliferation, and optimal cell adhesion. In vitro tests proved that HA/PMMA neurosurgical structures prepared by PLD and MS are compatible for the interaction with human bone cells. (C) 2010 Elsevier B.V. All rights reserved.

Implant type coatings were prepared by magnetron sputtering (MS) technique onto medical grade Ti6Al4V alloy substrates starting from biological 45S5 glass system powders. The as-deposited thin layers were annealed 2 h at 700 degrees C in ambient air, followed by a slow cooling (2 degrees C/min) in order to induce crystallization. The behavior of the coatings was investigated by soaking the samples in simulated body fluids (SBF) and extracting them after 24 and 72 h. The changes in the films' structure were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) analysis and by Fourier transform infrared spectroscopy (FTIR). A pitched, pore free microstructure with 6 mu m agglomerates of submicron grains in a continuous matrix was revealed by the SEM images of the annealed samples. Complex silicates as Na(4)Ca(4)Si(6)O(18)-combeite and phosphates NaCaPO(4) as crystalline phases were identified in the XRD diffraction patterns. In-growths after 24 h show the enrichment in Si-O (s) non-bonding oxygen (NBO). The polymerization reaction in the surface layer appears for the sample immersed 72 h in SBF. No crystalline hydroxyapatite (HA) was evidenced for those samples. Subsequent dissolution processes of the surface layers were noticed from XRD patterns and SEM images. (c) 2010 Elsevier B.V. All rights reserved.

A diode end-pumped Nd:YAG microlaser passively Q-switched by Cr4+:YAG with performances controlled by a volume Bragg grating (VBG) output coupler has been developed. Compared with operation at room temperature, the Q-switched laser pulse energy was increased, by a factor of 2 or more, by elevating the Nd:YAG temperature and locking the wavelength of emission with the VBG. Furthermore, the emission wavelength was tuned over 0.7 nm bandwidth by changing the VBG temperature while maintaining laser pulses of millijoule-level energy and short (less than 4 ns) duration. (C) 2010 Optical Society of America