Non-hydrogenated amorphous germanium carbide with adjustable microstructure and properties: A potential anti-reflection and protective coating for infrared windows

Amorphous non-hydrogenated germanium carbide (a-Ge_1-xC _x) films have been deposited using magnetron co-sputtering technique by varying the sputtering power of germanium target (P_Ge). The effects of P_Ge on composition and structure of the a-Ge _1-xC_x films have been analyzed. The FTIR spectrum shows that the C-Ge bonds were formed in the a-Ge_1-xC_x films according to the absorption peak at ~610 cm^-1. The Raman results indicate that the amorphous films also contain both Ge and C clusters. The XPS results reveal that the carbon concentration decreased as P_Ge increased from 40 to 160 W. The fraction of sp³ C-C bonds remains almost constant when increasing P_Ge from 40 to 160 W. The sp ² C-C content of a-Ge_1-xC_x film decreases gradually to 35.9% with P_Ge up to 160 W. Nevertheless, sp³ C-Ge sites rose with increasing P_Ge. Furthermore, the hardness and the refractive index gradually increased with increasing P_Ge. The excellent optical transmission of annealed a-Ge_1-xC_x double-layer coating at 400 °C suggests that a-Ge_1-xC_x films can be used as an effective anti-reflection coating for the ZnS IR window in the wavelength region of 8-12 μm, and can endure higher temperature than hydrogenated amorphous germanium carbide do.