Reactions of xenon difluoride and atomic hydrogen at chemical vapour deposited diamond surfaces

Abstract

X-ray photoelectron spectroscopy has been used to investigate the interaction of xenon difluoride at chemical vapour deposited, polycrystalline diamond surfaces. Dissociative chemisorption, resulting in the formation of adsorbed fluorine up to monolayer coverages, occurs on the clean surface with a sticking probability of approximately 10 −4. Prehydrogenation of the diamond, increases the initial reactive sticking probability, but reduces the saturation fluorine coverage observed. Two forms of adsorbed fluorine are clearly detected. The most thermally stable species, which is produced during initial xenon difluoride exposures, is attributed to covalently bonded carbon monofluoride functionalities. A second species, which is more weakly bound, has the characteristics of semi-ionic fluorine, which has been observed previously in the interaction of fluorine with other carbon forms. Thermal desorption studies show that the adsorbed fluorine desorbs over a large temperature range (40–800°C), reflecting the varying thermal stabilities of the differing populated states. Etching of a fluorine-saturated surface with hydrogen atom fluxes shows two main regimes; initial rapid removal of the semi-ionic fluorine species, followed by the very slow abstraction of covalent CF species. The comparative behaviour of the chemically vapour deposited diamond films with diamond single crystal surfaces, with regard to the chemistry observed, is discussed.