V. Buck

Preparation and properties of different types of sputtered MoS2 films

Abstract MoS 2 is widely used as a dry lubricant. For special applications, for example bearings for space mechanisms, it is applied in the form of sputter-deposited films. The lamellar structure of this material, the orientation of the lamellae and the stoichiometry of the coating are important in the sliding process and thus for the tribological performance. It is shown that these properties can be varied to a large extent by the variation of a single parameter in the deposition process. This parameter, which is usually not controlled quantitatively, is the amount of H 2 O present in the plasma. Furthermore, it is shown for the first time that all three different types of sputtered MoS 2 films, namely type I, type II and amorphous, can be produced by a variation in this parameter solely.

Pretreatment of substrate surface for improved adhesion of diamond films on hard metal cutting tools

Abstract The d.c. plasma jet CVD process is one of the most promising coating processes used for the production of polycrystalline diamond films. In comparison with other CVD processes, its obtainable linear growth rates, in the range of 100 μm/h, are much higher than growth rates of microwave or hot filament CVD (1–10 μm/h). One interesting application is the diamond coating of cutting tools. The main problem here is the poor adhesion of the films. Therefore, a mechanical or chemical pretreatment or intermediate layers are used to improve the adhesion. In these investigations the influence of mechanical pretreatment by grinding and polishing with diamond powder of different grain sizes as well as chemical etching are examined on WC-Co hardmetals. Sputtered metallic interlayers of different thicknesses and arc-ion plated amorphous carbon films are deposited on these substrates, and diamond films were synthesized on these pretreated cutting tools by d.c. plasma jet CVD. Adhesion and wear resistance of the diamond films have been examined by dry turning tests on very abrasive metal-matrix composites. Distinct improvement in adhesion of diamond coatings on hard metal substrates was achieved by two methods of substrate surface pretreatment: etching with Murakamis solution and following ultrasonically seeding with diamond particles or using an amorphous carbon film as intermediate layer.

Morphological properties of sputtered MoS2 films

As the lubricating properties of MoS2 are due to the sliding of lamellae, the crystallographic orientation and structural properties of these lamellae are important for the tribological behaviour. Thus an analysis of the growth morphology of sputtered MoS2 films was carried out. It is shown that morphological properties can be influenced by the parameters of the deposition process; in particular, it is possible to prepare coatings in which the lamellae are oriented parallel to each other.

A neglected parameter (water contamination) in sputtering of MoS2 films

Abstract A systematic study of the sources of contamination in sputtered molybdenum disulphide films is carried out. The only significant impurity from the deposition process is found to be water, which is present in trace amounts. The amount of this component is related to parameters of the coating procedure and can vary over several orders of magnitude. Quantitative relations for these effects are derived, conclusions concerning film properties are outlined and examples confirming the model are given.

LATTICE PARAMETERS OF SPUTTERED MOS2 FILMS

Abstract The stoichiometry, morphology and lattice constants of sputtered MoS 2 films depend mainly on the partial pressure of water during sputtering or rather on the substitution of sulphur by oxygen that follows from this contamination. Models describing the measured lattice contraction in the 001 direction and lattice expansion in the 100 direction with increasing oxygen content of the films are derived. Furthermore, the growth velocities of the grains are introduced as a second parameter to characterize the properties of the films.

Structure and density of sputtered MoS2-films

Abstract Methods for the determination of the density of sputtered films of MoS 2 are discussed and the problems connected with the determination of the film thickness are elucidated. The density determined for different coating parameters is given and the results are compared with the data of natural MoS 2 . The deviation from the bulk value is explained by morphological properties of the films. In addition, the influence of sputtering conditions on the structure of the films is mentioned and the results are correlated with these data.

Structural and optical properties of BaTiO3 thin films prepared by radio-frequency magnetron sputtering at various substrate temperatures

Thin films of BaTiO3 were prepared by radio-frequency magnetron sputtering at substrate temperatures from 450 to 750 °C and analysed by x-ray diffraction, optical transmittance and Raman spectroscopy. The packing density of the films relative to the crystalline density increases from 0.75 at 450 °C to about 1 at 750 °C. At a substrate temperature of 450 °C, the film is nano-crystalline (5 to 20 nm) with big lattice expansion, large band gap and pronounced hexagonal Raman lines. This film is homogeneous in the thickness direction. Films prepared at higher temperatures exhibit perovskite peaks in the Raman spectrum and an optical band gap of 3.38 eV. At 600 °C, the film exhibits a pronounced two-phase growth with a porous nucleation layer of initial packing density of 0.78, a preferred (100)-orientation of the grains and minimum micro-strain. At 750 °C, the films are again homogeneous in the thickness direction, have nearly crystalline packing density and preferably (110)-oriented grains.

Enhanced nucleation of diamond films on pretreated substrates

Abstract One interesting application of polycrystalline diamond films is the coating of cutting tools. The main problem herewith—the poor adhesion of the films—has been successfully overcome using mechanical or chemical pretreatments or intermediate layers. Besides adhesion, a significant aspect of film quality and performance is connected to size and orientation of the diamond grains, which depends on nucleation. In these investigations, different mechanical and chemical pretreatments as well as intermediate layers are produced to examine their influence on nucleation density, orientation of nuclei, etc. The effects of pretreatment on the nucleation process have been studied by EDX and scanning electron microscopy. It has been shown, for example, that the nucleation density can be significantly enhanced if combined methods of pretreatment are used.

Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: structure and osteoblast-like MG63 cells in vitro study

Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to −50 and −100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates.

Microanalysis and modelling of tribological coatings

Abstract The properties and tribological performance of sputtered MoS 2 films depend essentially on several chemical reactions, e.g. oxidation processes, that can be determined and explained quantitatively using different microanalytical techniques. By this method, stepwise systematic modelling can help explain many aspects of a films tribological behaviour, e.g. friction coefficient, wear life or the behaviour in a humid atmosphere.