Effect of Soft X-ray Irradiation on Film Properties of a Hydrogenated Si-Containing DLC Film

Abstract

The effect of soft X-ray irradiation on hydrogenated silicon-containing diamond-like carbon (Si-DLC) films intended for outer space applications was investigated by using synchrotron radiation (SR). We found that the reduction in film thickness was about 60 nm after 1600 mA·h SR exposure, whereas there was little change in their elemental composition. The reduction in volume was attributable to photoetching caused by SR, unlike the desorption of hydrogen in the case of exposure of hydrogenated DLC (H-DLC) film to soft X-rays. The ratio of the sp2 hybridization carbon and sp3 hybridization carbon in the hydrogenated Si-DLC films, sp2/(sp2 + sp3) ratio, increased rapidly from ~0.2 to ~0.5 for SR doses of less than 20 mA·h. SR exposure significantly changed the local structure of carbon atoms near the surface of the hydrogenated Si-DLC film. The rate of volume reduction in the irradiated hydrogenated Si-DLC film was 80 times less than that of the H-DLC film. Doping DLC film with Si thus suppresses the volume reduction caused by exposure to soft X-rays.

A review on diamond-like carbon-based films for space tribology

“…For example, although soft X-rays influence the whole F-DLC film instead of just the outermost surface, a low F content contributes to resisting soft X-ray irradiation [104,105]. Similarly, the presence of Si doping could restrict the desorption of hydrogen by X-ray irradiation [106,107]. Also, Liu et al [108][109][110] found that the liquid/DLC composite coating showed radiation resistance depending on its composition and structure.…”