Effects of deposition temperature on the properties of hydrogenated tetrahedral amorphous carbon

The properties of hydrogenated carbon films deposited from a highly ionized hydrocarbon plasma beam are studied as a function of deposition temperature. At low temperatures, the films have high sp(3) bonding, density, and compressive stress and are very smooth. Two transition temperatures are observed, a lower transition T-1 around 250 degrees C, dependent on ion energy, due to graphitization of C-C bonds, and a higher one T-2 at about 450 degrees C due to the loss of hydrogen. The roughness rises at T-1 and falls above T-2. These transitions are used to understand the subplantation deposition mechanism. The optical gap varies differently, decreasing gradually across T-1 due to ordering of sp(2) sites. We also report the temperature dependence of the x-ray diffraction. Raman spectrum, elastic modulus. hardness, substrate adhesion, friction coefficient, refractive index, and paramagnetic defect density. The friction coefficient of ta-C:H is low (0.05-0.1), and is maintained at ambient humidities, unlike for a-C:H. The friction mechanism is attributed to shear-induced graphitization. The spin density is found to decline with deposition temperature and the spin resonance line is argued to be exchange narrowed. (C) 1997 American Institute of Physics. [S0021-8979(97)03521-4].