National Institute Of Materials Physics - Romania

Thin films of Mg (x) Zn1-x O and Mg (x) Zn1-x O doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm(2) and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped Mg (x) Zn1-x O thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for Mg (x) Zn1-x O thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.

0.89(Na0.5Bi0.5)TiO3-0.11BaTiO(3), (BNT-BT0.11) thin film was fabricated by sol-gel/spin coating process, on platinized silicon wafer. Perovskite structure with random orientation of crystallites has been obtained at 700 A degrees C. Piezoelectric activity of BNT-BT0.11 thin film was detected using piezoresponse force microscopy (PFM). Effective piezoelectric coefficient d (33eff) of such film, recorded at 5 V applied dc voltage, was similar to 29 pm/V, which is similar to other BNT-BT (x) thin films. The complex refractive index and dielectric function of BNT-BT0.11 thin films were also investigated. The high leakage current density significantly influences the dielectric, ferroelectric, and piezoelectric properties of the BNT-BT0.11 films.

It is shown that the short-circuit photocurrent measured under illumination in Pb(Zr,Ti)O-3 epitaxial films is strongly dependent on the metal used as the top electrode. The magnitude of the photocurrent varies by more than 2 orders of magnitude from Pt (largest signal) to Al (smallest signal). The differences are for both directions of polarization. The imprint is also dependent on the top metal electrode, with a direct effect on the shape of the spectral distribution. The results support the hypothesis that the origin of the photovoltaic effect in ferroelectric thin films is different from that of the anomalous photovoltaic effect observed in bulk ceramics and single crystals. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624738]

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.

The paper focuses on the utilization of radiofrequency discharges at intermediate pressures for plasma removal of carbon residuals or layers from narrow gaps and channels. It is shown that by proper handling of the discharge power and pressure it is possible to control the development of plasma inside narrow gaps, in the proximity of surfaces to be cleaned. The discharge operation inside gaps having the width in the range 0.6-2 mm was demonstrated. The cleaning effectiveness is exemplified for castellated surfaces having rectangular gaps coated with hydrogenated amorphous carbon layers. Cleaning of large surfaces can be approached with a movable "plasma shower" type device. (C) 2011 Elsevier B.V. All rights reserved.

CeO2 films were prepared from solutions of different concentrations (0.05-1.0 M) on textured Ni substrates. Homogeneous nucleation and growth of CeO2 nanocrystals <8 nm occurs upon calcination at 350-500 degrees C. At the heating and sintering stage, the homogeneous growth is inhibited in favor of the development of grains with (0 0 1) texture. The grain growth normal to the film surface is well described by a stretched exponential function with a relaxation time of up to 60 min and with Kohlrausch exponent values of less than unity. The increase in grain size is accompanied by the relaxation of the microstrain. During the relaxation time, the grain coarsening is controlled by surface diffusion characterized by an activation energy as low as 0.6 eV. At the relaxation time, the surface morphology is strongly concentration dependent. The surface morphology changes from separated (agglomerated) grains to a continuous grain configuration as the concentration increases from 0.05 M to 0.8 M. After the relaxation time, both the grain size normal to the film surface and the lateral grain size continue to grow, and the grain configuration continues to change. These processes are concentration dependent. In the films with a nominal thickness >170 nm (>0.8 M), the transition to classical curvature-driven grain-growth kinetics is evident (at 1000 degrees C, below the literature value of 1100 degrees C). The decrease in the Kohlrausch exponent for these thick films suggests that the grain coarsening through grain boundary migration is responsible for the stretched regime of grain-size relaxation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ferroelectric ceramics Ba0.6Sr0.4TiO3 (BST 40) were prepared, by solid-state reaction in the temperature range 1210-1450 degrees C. Maximum values of the ceramic densities were around 94% of their theoretical value. X-ray diffraction techniques (XRD) and scanning electron spectroscopy (SEM) were used to analyze the structure and the surface morphology of ceramics. Rounded, well defined or abnormal granular growth was observed in the SEM images, vs. sintering conditions and purity of the raw materials. In all samples, BST 40 ceramic is the major phase, but there are also present small amounts of secondary phases, as revealed in XRD diffraction patterns. Permittivity and dielectric loss measurements were performed in the temperature range - 150 to + 150 degrees C, and 150 Hz-5 MHz frequency values. Permittivity values rising from 1200 to 12,500, with increasing sintering temperatures, were recorded. Narrow and well defined transition peaks were noticed at higher sintering temperatures. Curie temperature was around 2 degrees C, for samples with the mentioned composition. Permittivity and losses vs. frequency show different behavior whether BST ceramics are in polar or non-polar state and with the distance toward phase transition. Microwave measurements performed at room temperature have shown lower values of permittivity, compared with similar data at low frequency, and dielectric losses lower than 1% at 0.7 GHz. The sintering conditions (temperatures, sintering time, etc.) and purity of the raw materials lead to important changes of transition temperatures in the polymorphic diagram, which we have built-for the other Ba1 - xSrxTiO(3) compositions (x = 0.25-0.90) sintered at 1260 degrees C for 2 h. (C) 2011 Elsevier B.V. All rights reserved.

A general method for mapping the equipotential profile surrounding a conductive cylindrically symmetric high aspect ratio structure, such as a carbon nanotube or a Spindt tip, is devised. The surface of the object is replaced by a discrete set of charges located on the symmetry axis. The overall electrostatic potential must satisfy a set of boundary conditions imposed on the original surface. The optimum number of charges is determined through an iterative self-validating process such that the obtained equipotential mimics the surface of the object. The method is exemplified by calculating the electric field enhancement factor for rounded cones and cylinders resembling Spindt tips and carbon nanotubes, respectively. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3582141]

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns. (c) 2011 Elsevier B.V. All rights reserved.

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.