L'oxyde de vanadium amorphe hydrate

Hydrated amorphous vanadium pentoxide obtained by quenching of molten V₂O₅ in water is compared to amorphous V₂O₅ previously obtained by splat cooling. The first one contains some strongly bonded water which prevents crystallisation up to 300°C. Short range order around V⁴⁺ ions seems to be the same in both samples and in orthorhombic V₂O₅. Disorder in the amorphous phases leads to a localization of the charge carriers, the electron mobility being about ten times smaller than in the crystalline oxide.     

Verschleissfeste Antihaftschichten auf Basis modifizierter diamantähnlicher Kohlenstoffschichten

In this article technological developments in the field of modified diamond‐like‐carbon (DLC) coatings are described. The most well‐known properties of such DLC‐coatings are high hardness, high wear resistance, a very low friction coefficient (e.g. vs. Steel) and a very good chemical inertness. By doping the amorphous network with non‐metallic elements it is possible to influence the wettability of the DLC coatings over a wide range. This possibility to prepare a wear resistant sticking or non‐sticking DLC‐film opens a wide field of very different technical applications.     

Propriétés électriques des couches minces de GaSb amorphe

The electrical conductivity of sputtered amorphous GaSb films has been investigated as a function of the annealing conditions. The variation of the electrical conductivity with temperature may be explained in terms of a reduction of imperfections in the GaSb films. Following the model of Mott and Davis we calculate a conductivity gap of 0.76 eV for a stable amorphous state obtained by annealing at 210 °C.     

Hydratation et texture fibreuse de V2O5 amorphe

Reversible hydration of amorphous V₂O₅ has been performed in order to study the effect of water upon the properties of the oxide. A drastic change of the ESR spectrum is observed, which turns from anisotropic to isotropic upon hydration. This has been interpreted in terms of a brownian motion which, by analogy with the V₂O₅ gels, is supposed to be due to the fibrous texture of the amorphous oxide.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

Indice de réfraction du silicium amorphe hydrogéné préparé par glow discharge entre 95 et 723 K

Optical properties of hydrogenated amorphous silicon films prepared by glow discharge on fused quartz substrates held at temperatures T_s of between 50 and 350°C were determined from near-normal specular reflectance and transmittance measurements in the energy range 0.5–2.5 eV. The measurements were made at various temperatures T_m in the range 95–723 K. The refractive index dispersion data below the interband absorption edge were analysed using the Wemple and Didomenico model. The dispersion energy E_d of samples deposited at 280 and 350°C was found to be independent of T_m but a function of the hydrogen content for T_m < 573 K; the variation in the average gap E_m with temperature T_m was compared with the theoretical models of Varshni and Ravindra. For T_m > 573 K reversible or irreversible variations in the static refractive index n₀ lead to an increase in the dispersion energy owing to a rearrangement of the matrix with or without alteration of the hydrogen content. An interpretation in terms of rearrangement of the matrix under annealing without a decrease in the hydrogen content is proposed for the observed irreversible variations in the static refractive index n₀ of the film deposited at 50°C.     

Characterisation of amorphous carbon coatings for magnetic storage devices via AFM‐Nanoscratching devices. AFM‐Nanoscratching an amorphen Kohlenstoffschichten für die Speichertechnologie

The mechanical properties of ultra‐thin amorphous carbon films used as protective coatings for magnetic storage devices were investigated by means of atomic force microscopy (AFM). Diamond‐tipped cantilevers were used in order to generate scratches with residual scratch depths of only a few Angstroms and even below. The presented method simulates mechanical strains at the head‐disk interface. A driftcompensating image subtracting technique allows the visualisation of these ultra‐shallow scratches and enables the mechanical characterisation of only few Nanometer films widely independent from the hardness of the substrate. The scratch resistance as it is defined here correlates well with the mass density and the sp³ content of the investigated films.     

Obtention de films étain-azote par pulvérisation cathodique réactive-identification de la phase amorphe Sn3N4

The conditions for obtaining tin-nitrogen films by reactive cathodic sputtering in a d.c. system have been determined. The influence of the sputtering parameters on the deposition rate and the density of the films was studied. The amorphous nature of the films was demonstrated by electron diffraction. The different components were identified by microanalysis and infrared spectroscopy. The study shows that the films consist of an amorphous tin nitride matrix Sn₃N₄ containing molecular nitrogen and traces of free tin.     

Gap optique et indice de réfraction du silicium amorphe préparé par “chemical vapour deposition” entre 95 K et 673 K

The refractive index of silicon thin films prepared by chemical vapour deposition (CVD) was determined at various measurement temperatures T_m (T_m = 95?673 K in the energy range 0.5–2.0 eV. Using the Wemple-Didomenico model, we calculated the static refractive index n₀, the average energy gap E_m and the dispersion energy E_d for each measurement temperature. The dispersion energy is characteristic of the amorphous or the polycrystalline state; it changes very slowly with T_m. The variations in average energy gap E_m and in the optical gap E_g with T_m are similar; they can be described by the theoretical model of Varshni. Using the expression of Bahl and Baghat which relates the relative variations in optical gap ΔE_g/E_g with the variations in the static refractive index Δ_n0, we determined a characteristic valence band energy E_h. For amorphous silicon films prepared by CVD E_h seems to be independent of the substrate temperature T_s.     

Effet du champ électromagnétique fluctuant sur l'évolution des structures d'une couche métallique trés mince déposée sur substrat amorphe ou cristallin

It is believed that the grains of a thin metallic film are polarized by the electric field of “zero point” electromagnetic oscillations. This polarization causes a bipolar interaction force F which is calculated by using a bipolar approximation which is valid for short intergrain distances l.If the grains are not spherical, the curves F(l) generally exhibit a repulsive maximum between two ranges of the attractive forces. The curves F(a_) indicate the existence of a critical diameter (a_)_c. The grains are fixed by the repulsive forces for $\text{a}{}_{\mathrm{}}\text{? (a}{}_{\mathrm{}}\text{)}{}_{\mathrm{<mtext>c</mtext>}}$. Furthermore, a grain can only grow by the capture of impinging atoms or by the surface diffusion of adatoms.