National Institute Of Materials Physics - Romania

The nematic liquid crystalline mixture E7 was confined with similar filling degrees to molecular sieves with constant composition but different pore diameters (from 2.8 to 6.8 nm). Fourier transform infrared analysis proved that the E7 molecules interact via the cyanogroup with the pore walls of the molecular sieves. The molecular dynamics of the system was investigated by broadband dielectric spectroscopy (10(-2)-10(9) Hz) covering a wide temperature range of similar to 200 K from temperatures well above the isotropic-nematic transition down to the glass transition of bulk E7. A variety of relaxation processes is observed including two modes that are located close to the bulk behavior in its temperature dependence. For all confined samples, two relaxation processes, at frequencies lower than the processes observed for the bulk, were detected. At lower temperatures, their relaxation rates have different temperature dependencies whereas at higher temperatures, they seem to collapse into one chart. The temperature dependence of the slowest process (S-process) obeys the Vogel-Fulcher-Tammann law indicating a glassy dynamics of the E7 molecules anchored to the pore surface. The pore size dependence of both the Vogel temperature and fragility revealed a steplike transition around 4 nm pore size, which indicates a transition from a strong to a fragile behavior. The process with a relaxation rate in between the bulklike and the S-process (I-process) shows no dependence on the pore size. The agreement of the I-process with the behavior of a 5CB surface layer adsorbed on nonporous silica leads to the assignment of E7 molecules anchored at the outer surface of the microcrystals of the molecular sieves. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432775]

CuO/Al2O3 and NiO/Al2O3 catalysts prepared by incipient wetness impregnation were used for the oxidation of Reactive Black 5 (RB5) in aqueous solution. Removal of the dye was assessed by High Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) measurements and the generation of the hydroxyl radicals in the process was evaluated by chemiluminescence measurements. To put in evidence the interaction RB5 - catalyst and the surface species formed onto catalysts during the oxidation, Diffuse Reflectance Infrared Fourier Transform (DRIFT) analysis was performed. A different behavior of the two catalytic systems was revealed by the comparative analysis of the data obtained from the adsorption and oxidation tests. Only CuO/Al2O3 was effective in the RB5 degradation, NiO/Al2O3 acted as a simple adsorbent. In the presence of CuO/Al2O3, at H2O2 concentration of 40 mM the azo dye was totally eliminated from both solution and catalyst surface after 4 h, with a mineralization degree higher than 90%. However, a strong inhibition of the catalytic oxidation of RB5 was observed in the presence of phosphate ions. In the conditions of hydrogen peroxide excess, the rate equation in the case of copper catalyst was simply expressed by a pseudo-first order equation and the model was found to fit well the data. The amount of copper leached from catalyst during the oxidation process was only 1.0-1.6% per cycle leading to the conclusion that the decrease of the dye mineralization with the number of cycles has to be explained mostly by the surface covering with the reaction products, at least to a certain extent. (C) 2010 Elsevier B.V. All rights reserved.

Simple Fe-Co ferromagnetic films and Fe-Mn antiferromagnetic films of different compositions were grown on epitaxial Si substrates with Ta buffer layers via thermo-ionic vacuum arc method. Fe-Co/Fe-Mn bilayer structures were obtained by following similar growing conditions as for the simple films. The magnetic behavior concerning easy axis distribution, anisotropy energy and coercive field of the Fe-Co films exchange coupled to the antiferromagnetic layers were discussed with respect to the magnetic behavior of the simple, uncoupled, ferromagnetic films. The composition of the antiferromagnetic films has a sensible influence on the magnetic parameters of the exchange coupled ferromagnetic films. The largest coupling and the narrowest easy axis distribution are induced in the bilayer system with equatomic composition of the Fe-Mn antiferromagnetic layer. (C) 2010 Elsevier B.V. All rights reserved.

We report on pulsed laser deposition of TiO2 films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO2 lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO2 films was red-shifted up to similar to 480 nm from 360 nm in case of undoped ones. The photocatalytic activity of TiO2 films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO2 films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO2 structures deposited in pure methane and oxygen atmosphere. (C) 2009 Elsevier B.V. All rights reserved.

Aluminum doped Zinc Oxide (AZO) and Lithium doped Zinc Oxide (LZO) thin films are obtained by Pulsed Laser Deposition (PLD) method. These films are characterized by using Spectroscopic Ellipsometry (SE), X-ray Diffraction (XRD) and Photoluminescence (PL). By modeling the ellipsometry spectra we get the dielectric functions, the optical band gap E(g), and the electrical properties. Our results show the influence of the processing parameters on the optical and structural properties of doped ZnO thin films. The post-annealing treatment applied to AZO thin films, changes strongly the optical properties, by lowering the resistivity and red-shifting the band gap. (C) 2009 Elsevier B.V. All rights reserved.

Two series of cobalt substituted Ni-Fe-Ga ferromagnetic shape memory alloys with lower gallium content (< 27 at. %) were studied by differential scanning calorimetry, x-ray diffraction, and thermomagnetic measurements. Co substitution for Fe or Ni promotes an increase in the Curie temperatures and a variation in the martensitic transformation (MT) temperatures, in accord with the alloy valence electron concentration change. For alloys with MTs below room temperature, a field dependent thermomagnetic hysteresis was evidenced and discussed in connection with the effect of cobalt substitution, on the magnetic hardness of the martensite phase. A direct interpretation of the evolution of the thermomagnetic hysteresis versus the applied field was provided. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3429231]

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.