Mechanical properties and Raman characterization of amorphous diamond films as a function of film thickness

Amorphous diamond (a-D) films with different thicknesses have been prepared on the c-Si substrate under the same deposition conditions using filtered cathodic vacuum arc (FCVA) technology. The film thickness was measured with a calibrated surface profiler. The mechanical properties were analyzed by a nano-indenter and the microstructure was characterized with visible Raman spectroscopy. It has been shown that the residual compressive stress of a-D films drops continuously down with increasing film thickness. When the films are thinner, the stress falls strikingly. However, the falling rate is less pronounced with the monotonic increase in film thickness. Hardness and Young's modulus also persistently rise with growing film thickness. Whereas the critical scratching load decreases at first and then increases again. The peak position of the asymmetric broad peak in the Raman spectra shifts towards low frequencies with increasing film thickness because of the monotonic fall in the residual compressive stress. However, the magnitude of the shift is smaller. Additionally, the Raman characterization is apt to be taken in the film thickness scope of 50-80 nm.