National Institute Of Materials Physics - Romania

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.

The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In + Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In2O3), and counterbalance therefore the weak light absorption. (C) 2011 Elsevier B.V. All rights reserved.

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the radial mode, was proposed. This method uses the standard procedure to determine the elastic compliance and Poisson factor and the measurement of admittance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations. The accuracy of the new method was determined for materials with different planar coupling coefficients (k(p) = 2.5-57%) and mechanical quality factors (Q(m) = 20-3000). This method proved to be very accurate for all materials especially for those with large coupling factors. The accuracy of standard method was also evaluated for the same materials. (C) 2011 Elsevier Ltd. All rights reserved.

Imaging experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors with extraordinary performance specifications: doses of up to 1 GGy of 12 keV photons, up to 105 12 keV photons per 200 mu m X 200 mu m pixel arriving within less than 100 fs, and a time interval between XFEL pulses of 220 ns. To address these challenges, in particular the question of radiation damage, the properties of the SiO2 layer and of the SiSiO2 interface, using MOS (metal-oxide-semiconductor) capacitors manufactured on high-resistivity n-type silicon irradiated to X-ray doses between 10 kGy and 1 GGy, have been studied. Measurements of capacitance/conductancevoltage (C/GV) at different frequencies, as well as of thermal dielectric relaxation current (TDRC), have been performed. The data can be described by a dose-dependent oxide charge density and three dominant radiation-induced interface states with Gaussian-like energy distributions in the silicon band gap. It is found that the densities of the fixed oxide charges and of the three interface states increase up to dose values of approximately 10 MGy and then saturate or even decrease. The shapes and the frequency dependences of the C/GV measurements can be quantitatively described by a simple model using the parameters extracted from the TDRC measurements.

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.

The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.

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.

A new HA/Y2O3:alpha Al2O3 system was obtained by the deposition of a hydroxyapatite thin layer (similar to 150 nm), by magnetron sputtering, onto sintered substrates of low yttria (150 ppm) doped alumina. The yttria doped alumina was synthesized from very pure nanopowders, by mechanical homogenization, followed of pressing, sintering and different annealing regimes, in order to obtain bodies with various degree of nano-micro-structuration. TEM/HRTEM, SEM and EDS morpho-compositional analysis techniques were used to characterize the yttria doped alumina substrate and the hydroxyapatite superficial layer. The interfacial bonding strength between the sintered substrate and the hydroxyapatite thin film was analyzed by SEM. The evolution of the grains growth of the Y2O3:alpha Al2O3 substrate samples, with and without the hydroxyapatite covering layer is observed and discussed. A strong structural interdependence between the covering layer and the sintered substrate was emphasized. The grains' growth behaviour of the studied samples showed a linear evolution. A mathematical model for the grain growth process description was built, the grain size being interpreted as a random variable having a log-normal or Weibull probability density function.

The article reports on the tilted growth of textured aluminium nitride thin films obtained by radio-frequency magnetron sputtering onto 50 mm diameter Si (111) wafers, in reactive atmosphere, in a planar sputtering system without tilting the substrate and with no additional sputtering geometry alterations. The films were investigated using, X-ray diffraction, spectroscopic ellipsometry and scanning electronic microscopy, done by local measurements on the wafer surface, at different distances from the centre. A progressive increase of the tilt angle when moving away from the sample centre has been found. The maximum tilt angle of the columnar AlN crystallites, obtained near the edges of the wafer, is about 7 degrees. The results showed also that tilting is associated with smaller thickness and larger dispersion of the c axis orientation. Synthesizing inclined c axis AlN films should allow the fabrication of surface acoustic wave devices based on shear waves for liquid sensor applications.

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.