Effects of the chemical bonding on the optical and mechanical properties for germanium carbide films used as antireflection and protection coating of ZnS windows

Germanium carbide (Ge1-xCx) films have been prepared by RF reactive sputtering a pure Ge(111) target at different flow rate ratios of CH4/(CH4+Ar) in a CH4/Ar mixture discharge, and it has been found that the composition, chemical bonding, optical and mechanical properties of Ge1-xCx films are remarkably influenced by the flow rate ratio of CH4/(CH4+Ar). The effects of the chemical bonding on the optical and mechanical properties of the Ge1-xCx films have been explored. In addition, an antireflection Ge1-xCx double- layer coating deposited on both sides of the ZnS substrate wafer has been developed for application as an infrared window. It is shown that the transmittance in the wavelength region between 8 and 12 mu m and the hardness of the ZnS substrate have been significantly improved by the double-layer coating.