The CVD of Nanodiamond Materials

The growth and characteristics of nanocrystalline diamond thin films with thicknesses from 20 nm to less than 5 µm are reviewed. These materials contain between 95% and >99.9% diamond crystallites, the balance being made up from other forms of carbon. Within this class of materials there is a continuous range of composition, characteristics, and properties which depend on the nucleation and growth conditions. It is convenient to classify these films as either ultra‐nanocrystalline‐diamond (UNCD) or nanocrystalline‐diamond (NCD) based on their microstructure, properties, and growth environment. In general, UNCD materials are composed of small particles of diamond ca. 2–5 nm in size with sp 2 ‐carbon bonding between the particles. UNCD is usually grown in argon‐rich, hydrogen‐poor CVD environments, and may contain up to 95–98% sp 3 ‐bonded carbon. NCD materials start with high density nucleation, initiating nanometer‐sized diamond domains which grow in a columnar manner with the grain size coarsening with thickness. NCD is generally grown in carbon‐lean and hydrogen‐rich environments. NCD and UNCD exhibit an interesting range of physical properties which find use in X‐ray windows and lithography, micro‐ and nanomechanical and optical resonators, tribological shaft seals and atomic force microscopy (AFM) probes, electron field emitters, platforms for chemical and DNA sensing, and many other applications.