High density plasma processing of nanostructured diamond films on metals

Abstract

A new regime is reported for synthesis of nanostructured diamond films on Ti–6Al–4V alloy and molybdenum substrates using microwave plasma chemical vapor deposition (CVD) at high pressure (125 Torr) and high methane feed-gas concentration (5%–15% in a balance of hydrogen). These films are shown to be predominantly comprised of diamond nanocrystallites in a matrix of tetrahedral amorphous carbon. In contrast to standard CVD conditions, the high density plasma results in adhered films on the metal substrates even at substrate temperatures of 850 °C. These films are also significantly smoother than conventionally processed CVD diamond films and have a rms surface roughness of about 50 nm. The average grain size of these nanocrystalline diamond films is 13 nm as determined from x-ray diffraction data and the hardness of the films as determined from nanoindentation data is 90% that of natural diamond. Micro-Raman studies using 458 and 647.1 nm excitation indicate an increasing tetrahedral amorphous carbon content with increasing methane feed-gas concentration. The adhesion and mechanical properties of these films makes them attractive for a variety of tribological applications.