Showing papers by "Péter B. Barna published in 2004"

Nanostructured copper/hydrogenated amorphous carbon composite films prepared by microwave plasma-assisted deposition process from acetylene-argon gas mixtures

Abstract: Copper/carbon composite films have been deposited on Si substrates from argonacetylene mixtures using a hybrid technique combining sputter-deposition and plasma-assisted chemical vapor deposition. The carbon content in these films determined by Rutherford backscattering spectroscopy was varied in the range 5-99 at.%. The crystallographic structure was determined by X-ray diffraction techniques. The microstructure of films was examined by transmission electron microscopy. The magnitude of compressive residual stresses increased up to 0.5 GPa with increasing carbon content in the films. The hardness and elastic recovery of films determined by nanoindentation measurements were studied as functions of the composition of the gas phase. Low friction coefficient values were obtained from films containing more than 50 at.% of carbon in room air with a relative humidity of 50%. The wear resistance of films containing 23 to 29 at.% of carbon was higher by a factor of 2 than that of pure Cu films.

The investigation of multiply twinned L10-type FePt nanoparticles by transmission electron microscopy

Abstract: Thin films of FePt nanoparticles were prepared by co-deposition of Fe and Pt on to amorphous C films kept at 350°C. As-prepared films were composed of disordered Fe–Pt nanoparticles with a fcc structure, where twinned and multiply twinned Fe–Pt nanoparticles could be identified by transmission electron microscopy (TEM) and electron diffraction. Atomic ordering from fcc to L10 structure was followed by in-situ TEM observation during heating up to 750°C. Multiply twinned (fivefold) nanoparticles of the L10 FePt were observed for the first time by high-resolution TEM observation. In these nanoparticles the crystallographic c axes of L10 structure is oriented parallel to the film plane in each segment. The stability of the fivefold FePt nanoparticles is briefly discussed.

Self organised formation of layered structure in co-deposited Al–C thin films

Abstract: The structure formation of Al–C thin films has been investigated in samples prepared on a-SiO 2 /Si single crystal substrates by room temperature co-deposition. At higher C content, sequential growth of the Al/Al 4 C 3 microcrystalline composite structure and the metallic Al phase has been found in thick films (0.1–1 μm). This self-organised structure formation resulted in a layered phase structure. The microcrystalline composite structure is the first layer to develop on SiO x substrate and forms a layer of uniform thickness. This is followed by the growth of large polycrystalline Al islands which constitute a discontinuous layer with large surface roughness. At a certain stage of Al island growth the microcrystalline composite phase covers the Al crystal surface and the two processes are repeated. The structures formed at various film thicknesses were investigated by transmission electron microscopy and electron diffraction techniques.

Formation of embedded Co nanoparticles by reaction in Al/Co multilayers and impact on phase sequence

Abstract: The analysis of solid-state reaction in Al/Co multilayers shows that, after the first reaction step which is the formation of Al9Co2, the remaining Co “layer” can either be continuous or formed of Co nanoparticles. Simultaneously with this formation of Co nanoparticles we observe a bifurcation in the phase sequence, the second reaction product is different and its formation takes place at different temperatures. Thermodynamic considerations, namely modification of free energy by curvature and stress are used to explain that the change in the phase sequence is a result of the nanostructuration of the Co layer.