New developments in diamond and diamondlike coatings : preparation, properties and applications : report for 1990/1991

Preparation, properties and application of diamond and diamondlike coatings have been the subject of a recently published review /39/. The present review aims at presenting the newest trends and achievements in this extremely rapidly growingfield. Diamond has a unique combination of properties. It has the highest atom number density of any material at terrestrial pressures. As a consequence of its high atom-number density and the strong covalent bonding, diamond has the highest hardness and elastic modulus of any material and is the least compressible substance known /2/. The thermal conductivity of diamond at 300 K is higher than that of any other material (~1000 W/mK, compared to ~450 W/mK for copper, although thethermal conductivity of diamond films varies widely depending on their microstructure /25]/, and its thermal expansion coefficient at 300 K is only 0.8 x 10-6. Diamond has high chemical and wear resistance, optical transmission over a wide spectral range, high electrical resistivity and low friction coefficient in dry atmosphere. It can be considered as a semiconductor with a very wide band gap (~5.5 eV), high carrier mobility, breakdown voltage (10 7 V/cm), drift velocity and radiation hardness. However, it is the same group of properties that limits the exploitation of this material for technological applications because of difficulty of cutting, machining, manipulating and doping. The chemical vapour deposition (CVD) of diamond is receiving considerable attention because it is expected to provide the diamond layers with desired shape and properties. In the last several years an essential progress in the growth of diamond from gas phase has been made /39/. There is no longer any question as to whether or not diamond can be synthesized from the vapour phase. The research has come into a new phase in which the goal is to achieve good quality of the grown diamond. Indeed, the most recent literature on CVD of diamond, reviewed in this study, leaves the general impression that the interest in diamond deposition has become extremely [...