The effects of deposition parameters on the deposition rate, microstructure, and composition of Ge1-xCx thin films prepared by plasma enhanced chemical vapor deposition were studied and the films' infrared optical properties were investigated. The results show that the carbon content of these films increases as the precursor gas flow ratio of CH4:GeH4 increases, while the infrared refractive index of these films decreases from 4 to 2. The deposition rate increases with the radio-frequency power and reaches a constant value when the power goes above 60 W Gel(1-x)C(x)/diamolid-like carbon infrared antireflection coatings were prepared, and the transmittance of the coatings in the band of 8 to 14 mu m was 88%, which is superior to that of Zinc Sulfide substrate by 14%. (c) 2007 Elsevier B.V All rights reserved.