Theoretical and experimental studies related to the compositional and microstructural evolution of alumina thin films
In this thesis, the correlation between plasma chemistry / ion energy and thin film composition / microstructure for cathodic arc deposited alumina thin films is investigated. To contribute towards understanding this correlation, both theoretical and experimental investigations have been performed. The plasma, constituting the feed-stock material for the film growth, was characterized with respect to chemistry, for a pulsed arc showing a temporal dependence from pulse-to-pulse as well as within a pulse. Further plasma analysis of a DC arc source showed charge- and pressure dependent ion energy distributions including ions in excess of 200 eV, which could be manipulated by suitable magnetic field configuration. Based on the here determined plasma composition data, thin film growth related theoretical studies have been carried out, using ab initio calculations and ab initio molecular dynamics simulations based on Density Functional Theory. The sequence of an ion approaching and being incorporated in the top surface layers was divided into separate investigations related to structural evolution; ion-surface interaction prior to adsorption, adsorption, surface migration and local structural changes induced by ion bombardment. The results may in part explain the experimentally observed formation of amorphous structures during kinetically limited alumina film growth. Furthermore, possible hydrogen incorporation in the film due to presence of residual gas motivated a study related to compositional evolution. The simulation results suggest that hydrogen desorption upon ion – surface interaction may be possible. To correlate theoretical studies and synthesis conditions with phase formation, experiments were performed to investigate the effect of ion energy and substrate temperature on the film composition and microstructure. It was found that the structure evolution strongly depends on the to the surface supplied energy, and that γ-alumina forms at temperatures as low as 200ºC. Analysis of the film composition showed a low concentration of impurities, with less than 0.25 at% hydrogen. Hence, the results presented in this thesis may provide pathways to crystalline film growth at low temperatures as well as to reduction of impurity incorporation during film growth.
info:eu-repo/classification/ddc/620, Aluminiumoxide, Schichtwachstum, PVD-Verfahren, Bogenplasma, Ingenieurwissenschaften, alumina, arc, plasma, structure, composition
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