Publications

A far-from-equilibrium preparation route and using a particular combination of starting materials led us to obtain nonstoichiometric Y(Fe,V)(12) and its interstitial carbide. Structural analysis and EDAX results reveal the formation of the main 1:12 phase with the ThMn12-type structure, with 13-15% vacancies at the 3d metal sites. Insertion of interstitial carbon increases the T-C and magnetization of the 1:12 phase, whereas the unit cell volume remains unchanged. The effects of vacancies and interstitial carbon on the Mossbauer hyperfine fields and isomer shifts are discussed with reference to the calculated quantities. (C) 2000 Elsevier Science S.A. All rights reserved.

The morphology and structure of a La0.6Y0.07Ca0.33MnO3 thin film is studied by transmission electron microscopy. The film was grown by pulsed laser deposition (PLD) on an MgO-buffered silicon wafer. The as-deposited films are polycrystalline and show a columnar morphology. We present a detailed high-resolution transmission electron microscopy structural study concerning a possible monoclinic distortion of the orthorhombic LYCMO crystal cell. (Received February 22, 2000; accepted March 10, 2000).

Elastic recoil detection analysis (ERDA) has been applied to determine the composition of carbon nitride and hydrogenated carbon nitride films prepared by hollow cathode discharge process. The films were deposited on Si (111) substrates. The films were also characterized by Fourier transform infrared spectroscopy (FTIR). The influence of the main deposition parameters (substrate bias voltage, nitrogen injection mode) on the film properties was investigated. (C) 1000 Elsevier Science B.V. All rights reserved.

Carbon nitride thin films (CNx) were produced by UV laser (ArF, lambda=193 nm) induced chemical vapour deposition from C2H2/NH3 mixtures, on Si and TiN/Si substrates. The surface and bulk composition of the deposited layers were investigated by X-ray photoelectron spectrometry (XPS) and elastic recoil detection analysis (ERDA), respectively. Nitrogen was found to be singly and doubly bonded to carbon, as revealed by FTIR spectrometry. Specific morphology of the films was evidenced by transmission electron microscopy (TEM), while selected area electron diffraction (SAED) confirms the presence of nano-crystallites in the layers. The calculated d-lattice spacings fit rather well with theoretical and experimental data for alpha- and beta-C3N4. (C) 2000 Elsevier Science S.A. All rights reserved.

Photostimulated luminescence (PSL) and diffuse reflectance measurements on X-ray irradiated BaFCl:Eu2+ microcrystalline powders were performed. We have investigated the nature of radiation induced defects involved in the photostimulation effect and its recombination mechanism. The experimental data sustain that X-ray irradiation gives rise to (F(Cl-) - O-F(-) - EU2+) photostimulable complexes and we have proposed several geometrical configurations of these complexes. (Received January 27, 2000; accepted February 16, 2000).

The formation mechanisms of nanocrystalline composite structures are discussed, and results on co-deposited material system of C-60-Au, C-60-Cu as well as Al-SiOx are presented. Three type of structures are distinguished in the composite films, depending on the concentration of the additive. The decisive structure-forming phenomena are the kinetic segregation of the minority species and the chemical reaction of the deposited components. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Photodarkening relaxation under light exposure of a-As2Se3 amorphous films doped with 0.5 at.% tin, manganese, samarium and dysposium, separately introduced, was studied in dependence on the impurity type and thermal annealing. Both factors reduce photodarkening and the degree of reduction depends on the type of impurity. The relaxation process may be described by a stretched exponential with the dispersive parameter 0.5<alpha<l and time constant increasing by thermal annealing. The results are discussed in the frame of recently proposed "slip-motion" model of photodarkening in chalcogenide glasses. (Received February 11, 2000; accepted February 29, 2000).

This work is a comparative study of the structural and magneto-transport properties of La0.60Y0.07Ca0.33MnO3-delta (LYCMO) as bulk and thin film. The bulk samples were prepared by solid-state reaction between the corresponding metallic oxides mixed in stoichiometric ratios. The thin film was deposited by pulsed laser deposition on an MgO single crystal using an excimer laser. We show that the structure and stoichiometry of the bulk target are perfectly reproduced in the thin film. We measured the magnetoresistive effect on both the LYCMO pellet and the thin film by using the four-probe technique. The maximum of the MR effect is 680% on the polycrystalline thin film in a 2T magnetic field. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

A Monte Carlo calculation is presented for the instrumental luminosity, instrumental peak profile and instrumental peak shift for a neutron powder diffractometer in focusing geometry with pneumatically bent monochromator crystal and thin plate sample. (C) 2000 Elsevier Science B.V. All rights reserved.

The collapse of the magnetic hyperfine structure of barium hexaferrite as an effect of mechanochemical activation was investigated. The various inequivalent sites and phases present in the milled material were studied by transmission Mossbauer spectroscopy. Barium hexaferrite nanoparticles were obtained after only 2 h of milling time and were found to coexist with iron oxide particles for longer times of exposure to mechanochemical activation. The milled samples were then subjected to thermal annealing, in order to test the reversibility of the collapse of the hyperfine structure. The thermal annealing performed (700 degreesC, 1 h) was partly successful in restoring the magnetic hyperfine structure of milled hexaferrite. Complementary information was obtained using transmission electron microscopy (TEM) and electron diffraction (ED).