Bipolar pulsed sputtering of MoSx coatings: plasma diagnostics, micro-structural and tribological study

Abstract

MoSx coatings were deposited by magnetron sputtering of an MoS2 target in an argon atmosphere with different process parameters. Their composition, surface morphology and structure were determined, and the friction and wear behaviour of these coatings were evaluated under fretting tests in air of< 10% and 50% or even 90% RH. The results obtained in this thesis indicate that the properties of sputtered MoSx films are influenced in a complex manner by the main process parameters. To establish a deep understanding between these parameters, the micro-structural properties and the tribological properties of the MoSx films, the energy distribution of neutral and ionised particles impinging on the growing film was studied by means of energy resolved mass spectrometry. T he results can be summarised as follows: MoSx coatings can be prepared either with the basal (002) planes oriented parallel to the substrate or with random or preferential edge orientation. Films with basal plane orientation are only obtained when they are deposited by bipolar pulsed sputtering at 0.4 Pa argon pressure and with a target current of 0.6 A. These films have a low sulphur to molybdenum ratio, contain approximately 4 At% Ar and exhibit a dense and featureless morphology. Using BPDC sputtering at high argon pressures or different target currents or using UPDC or DC sputtering results in films with a preferential edge or random orientation. Generally, these films have a higher sulphur to molybdenum ratio, a lower argon content and show a porous, worm-like morphology. ... (Excerpt from the conclusions)