INDENTATION RESPONSE OF DIAMOND THIN-FILMS

The high hardness and elastic modulus of diamond, together with its relative chemical inertness and high thermal conductivity, make it an excellent candidate material for sensing applications involving exposure to extreme conditions. With the emergence of CVD diamond technology it has become possible to deposit thin diamond films onto a range of substrate materials. However, it is important that reliable property measurements be made on the coatings, a very exacting task. In this study the mechanical properties of diamond films deposited by microwave and thermal filament CVD were investigated by two indentation techniques, direct low load measurements using a nanoindenter and an indirect modelling route using conventional Vickers indentations. The results of the two techniques were correlated to determine the effect of the measurement route on the mechanical properties determined. In general, the ranking of the hardness of the films deposited by the two techniques is similar, with the microwave CVD films being considerably softer although the hardness of the films does depend on the choice of process parameters used in each technique. The hardness of the film is dominated by the yield or fracture properties of the diamond crystal with the small grain size of the coatings contributing only a small proportion of the measured hardness.