[en] We report on the effects of the substrate and the thickness on the physical properties of Ni thin films. Ni films with thickness ranging from 17.0 nm to 107.0 nm have been deposited thermally on Si(100) and Si(111) substrates and on glass. Rutherford backscattering spectrometry, scanning electron microscopy and X-ray diffraction experiments have been performed to study the structural properties of these samples. It is found that all Ni films evaporated on glass and on Si(100) substrates have <100> orientation. For the Ni films evaporated on Si(111) substrates, a change of texture from <100> to <111> is observed as the film thickness increases. The lattice constant and grain size are discussed as a function of substrate and thickness. Electrical properties have been also studied using the four point method (Authors)

[en] The luminescence of three compounds: LuBO₃, with calcite and vaterite structures, and YBO₃ (vaterite structure) doped with Pr³⁺ ions has been investigated. The emission was ascribed to four spin-allowed transitions and one spin-forbidden transition from the 4f5d to the 4f² configuration. Two additional broad emission bands with very weak intensity at 440 and 580 nm were studied. Evidence of the presence of Ce³⁺ traces is reported and their influence on Pr³⁺ luminescence is discussed. (authors)

[en] We report on the effect of thickness on the structural and optical properties of TiO₂ thin films obtained by direct exposure of Ti metal film to thermal oxidation. Ti thin films with thicknesses ranging from 87 nm to 484 nm were deposited onto glass substrate by RF magnetron sputtering. Thereafter, the as-deposited Ti films were annealed in air at temperature equal to 520 deg. C. The structural evolution and optical properties of obtained TiO₂ films were studied by means of Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and UV-Visible spectroscopy. The films thicknesses were extracted from RBS spectra. From X-ray diffraction spectra, we can see that all the films present three TiO₂ phases (anatase, rutile and Brookite). The anatase and rutile phases exhibit a strong preferred orientation along (004) and (210) planes respectively. The grain sizes, D (nm), did not change much with increasing thickness. The average value of < D>(nm) was equal to 29 nm for anatase and 26 nm for rutile. The micrographs taken from SEM experiments indicate that the films present a dense micro structure with very small grains. Transmittance spectra show that all the films present a good transparency in the visible region. The dependence of transmittance, optical band gap and refractive index on the thickness of the films was also studied.

[en] The damaged produced by proton beam slowed down in CR-39 polymer results in highest degree of disorder with change of free volume proprieties. Positron annihilation lifetime spectroscopy (PALS) is nowadays well recognized as powerful tool of microstructure investigations. PALS is used in order to get more information at an atomic scale of modifications induced by irradiation of polymers particularly the variation of free volume in the irradiated region. In this paper, the mean free volume hole radii and average free volume of the micro-voids in CR-39 polymer irradiated with 200 MeV therapy proton beam at different positions in spread out Bragg Peak region (SOBP) at Ithemba proton therapy facility have been determined using PALS. © 2006 Elsevier Ltd. All rights reserved. - Highlights: ► PALS is useful tool to study radiation effect on CR-39 Polymer. ► Irradiations were performed with 200 MeV proton beam at the SOBP region. ► Small decrease in o-Ps lifetime shows reduction of free volume in irradiated CR-39. ► This reduction indicates the facilitation of cross linking in the damaged region. ► Distribution of deposited energy per unit volume is not uniform at the SOBP region

[en] We report on the synthesis of Co₃₀Ni₇₀ nanoparticles using hydrothermal method at low temperatures and short times (100 °C, 2 h) without any surfactant or external magnetic field. The effect of NaOH concentration on the crystal structure, microstructure, and magnetic properties of CoNi samples has been investigated by x-ray diffraction (XRD), scanning (SEM) and high-resolution transmission (HRTEM) electron microscopy, and vibrating sample magnetometry (VSM). From the Rietveld refinement of x-ray powder diffraction patterns, we have evidenced the coexistence of two phases with face-centered cubic (FCC) and hexagonal (HCP) crystal structures, being 12 nm and 3 nm, respectively, the values for the mean grain size of both phases. SEM images show that the basic microstructure is composed of quasi-spheres and a chain-like morphology appears with increasing the amount of NaOH. HRTEM images evidence the formation of such chains, and confirm the coexistence of FCC and HCP phases. The magnetic hysteresis loops show a clear dependence of the coercivity on the particle morphology indicating the role played by the magnetic shape anisotropy.

[en] We have prepared solid thin film samples of SnO₂:Sb in different ratios using atmospheric pressure chemical vapour deposition technique APCVD. The chemical composition was determined with Rutherford Backscattering Spectroscopy (RBS) within an error of 1%. X-ray diffraction was used to study the influence of Sb concentration on the lattice parameters and preferred orientations. We have found that sample of concentration 4% showed a (200) preferred orientation. The AFM and SEM images showed that the surface roughness of our samples was influenced by the doping concentrations. The lowest electrical surface resistance was 8.0 Ω □⁻¹ for a 3% concentration sample. We found that the contribution to the metallic state is influenced by oxygen vacancy and Sb doping. Also, the sample of good electrical conductive property has an optical gap of 3.60 eV band at room temperature. - Highlights: ► The thickness was a nonlinear function of the reaction time. ► Minimal value of 8.0 Ω □⁻¹ for a 3% concentration and 3.60 eV energy gap. ► Surface morphology is dopant dependant

[en] Wurtzite zinc oxides films (ZnO) were deposited on silicon (0 0 1) and corning glass substrates using the pulsed laser deposition technique. The laser fluence, target-substrate distance, substrate temperature of 300 deg. C were fixed while varying oxygen pressures from 2 to 500 Pa were used. It is observed that the structural properties of ZnO films depend strongly on the oxygen pressure and the substrate nature. The film crystallinity improves with decreasing oxygen pressure. At high oxygen pressure, the films are randomly oriented, whereas, at low oxygen pressures they are well oriented along [0 0 1] axis for Si substrates and along [1 0 3] axis for glass substrates. A honeycomb structure is obtained at low oxygen pressures, whereas microcrystalline structures were obtained at high oxygen pressures. The effect of oxygen pressure on film transparency, band gap E_g and Urbach energies was investigated.

[en] Nanostructured Fe₅₀Co₅₀ powders were prepared by mechanical alloying of Fe and Co elements in a vario-planetary high-energy ball mill. The structural properties, morphology changes and local iron environment variations were investigated as a function of milling time (in the 0-200 h range) by means of X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis and ⁵⁷Fe Moessbauer spectroscopy. The complete formation of bcc Fe₅₀Co₅₀ solid solution is observed after 100 h milling. As the milling time increases from 0 to 200 h, the lattice parameter decreases from 0.28655 nm for pure Fe to 0.28523 nm, the grain size decreases from 150 to 14 nm, while the meal level of strain increases from 0.0069% to 1.36%. The powder particle morphology at different stages of formation was observed by SEM. The parameters derived from the Moessbauer spectra confirm the beginning of the formation of Fe₅₀Co₅₀ phase at 43 h of milling. After 200 h of milling the average hyperfine magnetic field of 35 T suggests that a disordered bcc Fe-Co solid solution is formed. - Highlights: → Nanostructured Fe₅₀Co₅₀ powders were successfully prepared by mechanical alloying process. → Final average grain size value achieved after 200 h of milling was 14 nm. → For the longest milling time the majority of particle grains observed by SEM exhibits a round shape with small diameter.

[en] Highlights: ► Nanocrystalline Fe₇₀Al₃₀ powders were successfully elaborated by mechanical alloying. ► The Mössbauer spectra show that from 4 h of milling, a disordered ferromagnetic. ► Fe₇₀Al₃₀ starts to form and dominates after 36 h. - Abstract: We have studied the effect of milling time on the structural and hyperfine properties of Fe₇₀Al₃₀ compound elaborated by mechanical alloying. The elaboration was performed with a vario-planetary ball mill P4 at different milling times. The milled powders were characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. From XRD diffraction spectra, we show that the bcc Fe(Al) solid solution was completely formed after 27 h of milling time. When the milling time increases, the lattice parameter increases, whereas the grain size decreases and the mean level of microstrains increases. The analysis of Mössbauer spectra shows that from 4 h of milling, a disordered ferromagnetic Fe₇₀Al₃₀ starts to form and dominates after 36 h.

[en] We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut conditions. By using transmission electron microscopy, we found that the damage band in as-implanted GaN is decorated with a high density of nanobubbles of ∼1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of V_Ga, V_Ga-H₂, and V_GaV_N complexes was evidenced by pulsed low-energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open-volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450 deg. C, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Since the formation of positronium is not possible in a dense semiconductor, our finding demonstrates the presence of sufficiently large open-volume defects in this temperature range. Based on the Tao-Eldrup model, the average lattice opening during thermal annealing was quantified. We found that a void diameter of 0.4 nm is induced by annealing at 600 deg. C. The role of these complexes in the subsurface microcracking is discussed.