Tuning of the microstructure, mechanical and tribological properties of a-C:H films by bias voltage of high frequency unipolar pulse

Amorphous hydrogenated carbon (a-C:H) films were prepared by high frequency unipolar pulse plasma-enhanced chemical vapor deposition in CH4, Ar, and H2 atmosphere with the bias voltage in the range of −800 -−1600 V. The microstructures and mechanical properties of a-C:H films were investigated via high resolution transmission electron microscope (HRTEM), Raman spectroscopy, and Nanoindenter. The results reveal that the curved and straight graphitic microstructures appear in amorphous carbon matrix, and their contents increase obviously with the bias voltage. At the same time, the corresponding hardness decreases and elastic recovery increases, however even in such a case films still possess excellent mechanical properties. According to the tribological property characterization, we believe that the bias voltage also influences their tribological performances significantly, the higher the bias voltage finally gets, the lower the friction coefficient and wear rate occur. These results indicate that the microstructures of a-C:H films can be tuned efficiently by bias voltage and the films with good mechanical and tribological properties can be obtained at a higher range.