Mechanical properties of nanocrystalline diamond films

Nanocrystalline diamond (NCD) films with thicknesses in the range of 0.12–1.5μm were deposited on silicon substrates in CH4∕H2∕O2 gas mixtures by microwave plasma-enhanced chemical vapor deposition. The morphology and structure of these NCD films were analyzed by field-emission scanning electron microscopy, x-ray diffraction (XRD), and ultraviolet-Raman spectroscopy. The lower limit of the grain size in the NCD films was estimated to be 10nm from the XRD measurements. These grains are embedded in a columnar-type structure. The elastic and mechanical properties of the NCD films were determined by measuring the dispersion of laser-induced surface acoustic waves. The densities were in the range of 3.41±0.11g∕cm3 and Young’s moduli varied between 674±34 and 953±48GPa, depending on the growth time and deposition conditions. It is concluded that oxygen may have a significant positive effect on the elastic properties of NCD films. The growth rate decreases sharply for an oxygen content in the source gas in excess of about 4%.