Hard amorphous (diamond-like) carbons

The hard forms of amorphous carbon and hydrogenated amorphous carbon, also known as diamond-like carbon, have recently aroused considerable interest as coating materials. This paper reviews their preparation, structure and properties. These carbons contain both sp² and sp³ sites. A chemical bonding model is developed which describes the arrangement of these sites and which accounts for many of the electronic and mechanical properties. The review covers the various deposition methods and the deposition mechanisms, the characterisation of amorphous carbons by techniques such as diffraction, electron energy loss, Raman, infra-red, nuclear magnetic resonance, and thermal stability, their electronic structure, optical properties and electronic spectra, and their mechanical properties such as elastic modulus, hardness, wear rate, friction and film adhesion. The dependence of electronic and mechanical properties on deposition methods and conditions is studied, to assess which methods are most valuable for applications.