Diamond-like carbon (DLC) films have been deposited by RF plasma-assisted chemical vapor deposition from acetylene at temperatures of 100–250°C, power densities of 0.1-0.2 W • cm -2, and substrate biases of —80 to —200 V dc. The films have been annealed in vacuum at temperatures up to 590°C for 3–4 h. Ellipsometry and Fourier transform infrared spectrometry have been used to characterize the optical properties of the films while the hydrogen concentration has been measured by forward recoil elastic scattering. The wear resistance of the thin DLC films and their friction coefficients have been characterized by a pin-on-disk type tribotester. The hydrogen content of the DLC films was found to decrease after annealing in vacuum above 390°C, yet approximately 20% hydrogen was retained in all the films after annealing at 590°C. The index of refraction of as-deposited films or postannealed at up to 390°C was found to be independent of the deposition temperature for a given substrate bias. Although the index of refraction was found to increase with decreasing hydrogen concentration during annealing above 390°C, higher indexes of refraction were obtained for films of identical hydrogen content but deposited at higher power and bias. The sp2:sp3 carbon ratio increases with increasing annealing temperature, and only sp2-bound carbon is identified in the Fourier transform infrared spectra after annealing at 590°C. The wear resistance of the as-deposited DLC thin films in nitrogen is not affected by the deposition parameters in the investigated range. However, better stability to higher annealing temperatures was observed for DLC deposited at higher temperature or higher bias. The highest thermal stability was obtained for DLC films deposited at 250°C and —150 V, which remained wear-resistant in nitrogen even after annealing at 590°C. © 1991, The Electrochemical Society, Inc. All rights reserved.