Papers by Keyword: Surface Composition

Abstract: The surface lanthanum element plays a key role in emission mechanism of Lanthanum-contained cathodes. In order to gain insight into the relation between cathode emission properties and the cathode surface La/O ratio, lanthanum-rich film cathodes were prepared in situ by using a set of equipment, specially designed to cathode research, which connected with an Auger electron spectrometer (AES) and pulse laser deposition system. Electron emission properties and surface compositions (lanthanum and oxygen) of the cathodes are investigated experimentally. Experiment results indicate that film cathodes are lanthanum-rich film cathode, there has remained unchanged on film composition in different depth; the cathode emission properties are determined intensively by the surface atomic La/O ratios, the higher the La/O ratio gets, the better the emission property reaches. The excess active Lanthanum is crucial element to the improvement of emission properties.

Abstract: The real structure of nanocrystalline CeO2-ZrO2 (Ce:Zr=1:1) systems prepared via the polymerized polyester precursor (Pechini) route and doped with La3+ or Gd3+ cations, up to 30 at.%, was studied by X-ray powder diffraction, EXAFS and Raman spectroscopy and the surface features characterized by XPS and SIMS. Undoped CeO2-ZrO2 system revealed nanoscale heterogeneity, perhaps due to the co-existence of Zr- or Ce-enriched domains. With large La3+ dopant the system remains bi-phasic within the studied ranges of composition, incorporation of the smaller Gd3+ cation stabilizes the single-phase solid solution. For both systems, the increase of dopant content was accompanied by a decline of domain size and an increase of the average lattice parameter of fluorite-like phases. Depletion of the surface layer by smaller Zr4+ cations was observed, while the surface content of a doping cation is either, close to that in the bulk (La) or below it (Gd). Such a spatial distribution of components results in some ordering of cations within the lattice. It is reflected in different modes of rearrangement of oxygen coordination polyhedra with the Gd or La content (distances and coordination numbers by EXAFS), and specificity of XRD patterns not conforming to a simple model with statistical distribution of oxygen vacancies.

Abstract: Understanding of interaction reactions between materials and tissue in the body is necessary for the success of implant devices. Impedance and polarisation properties at the interface on 316L stainless steel and pure Ti under cell culture environment of fibroblast L929 or with collagen coating were examined. Limitation of mass diffusion at the interface by cell bodies and extracellular matrix is probably a corrosion factor of the presence of cells, which causes the decrease of protectiveness of passive film on 316L steel. Surface composition of 316L steel and Ti formed with L929 was compared with that formed in human body. Similar elements were detected on the surface formed in both the environments. The precipitated sulphur on the surface formed under cell culture and in the human body appears to be originated from proteins that might be produced by cells.

Abstract: PE is manufactured by Transysteme with the method of thermocompression of PE powder. This company irradiates PE by YAG LASER. We compared the physical behavior of both samples. The DSC reveals a high and similar crystallinity of PE, before and after YAG LASER treatment. Weattability between PE and Li-PE are similar at about 37 mJ/cm². The difference appears with respect to the surface profile and composition: the roughness is 0.20 µm for PE and 0.29µm for Li- PE. XPS reveals many traces of stripping agents on PE. YAG Laser produces a surface cleaning effect. Biological tests reveal a non-toxicity of the polyethylene powder, an improved proliferation and vitality of L132 cells on Li-PE with respect to untreated PE. We have a 4-fold improvement of proliferation and a 2-fold improvement of vitality on Li-PE with respect to PE. As to morphology and cell adhesion behavior, we have no differences between both samples. Thus the irradiation process of PE by YAG LASER improved the biological behaviors of this polymer due to changes in roughness and to surface cleaning.

Abstract: Surface atoms are activated as result of replacement collisional sequences in solids by incident ions. In dependence on theirs threshold (displacement) energy and angular distribution they may be sputtered (removed) or laterally relocated on the surface. The relocation length distribution depends on the energy and angular distributions of activated atoms and interaction atom-solid potential. The process of lateral relocation of surface atoms is considered as a sequence of stochastic removal and adsorption processes. The rate equations describing processes of sputtering, relocation and thermal diffusion are built and steady state solutions are presented for multielemental solids. The mechanisms of stochastic mixing of atoms and roughening of surface is discussed.