Diamond as an industrially important material achieves unique status as a result of the remarkable series of physical properties it possesses. Diamond is the hardest known material, it has the highest thermal conductivity, the highest electrical resistivity and the largest band gap of all the semiconductors. In table 1 some key properties of diamond that find use in hard coating applications are shown and comparisons made with other materials where appropriate. As a result of its properties diamond coatings, films, sheets, slabs and three dimensional shapes can find wide use in a large variety of industrial applications.

There are several reasons why diamond is not widely used despite its unsurpassed physical properties: a) the high cost and rarity of naturally occurring diamond b) the complexity of synthetic diamond fabrication processes which require extreme temperatures and pressures, and c) the lack of availability of films or two dimensional sheets in either naturally occurring diamond or in high pressure synthesized diamond.

The recent development of low pressure vapor deposition techniques for diamond films have dramatically changed the prospects for the practical utilization of diamond of various forms in various applications (D. The ability to synthesize diamond from methane and other hydrocarbons and deposit the diamond on a variety of substrates opens up a vast arena of uses. The unique properties of diamond will extend the capabilities of products and processes as well as open up the possibility of an entirely new class of applications. PECVD ( Plasma Enhanced Chemical Vapor Deposited) diamond films of thicknesses ranging from a few hundred nanometers to tens of micrometers have been reported.

The extreme differences in properties between graphite and diamond belie the fact that they are two crystalline modifications of the same element differing in stability by a mere 0.6 Kcal/mole at room temperature. The prediction of the precise temperature and pressure conditions for the conversion of graphite to diamond from simple thermal measurements is an outstanding success of classical thermodynamics and is the basis for the commercial high pressure synthesis of diamonds. This method, however, is expensive and is limited in the size, shape and perfection of the diamond. The new method of diamond synthesis - plasma enhanced chemical vapor deposition (PECVD)- is now under development in various organizations around the world 0"13).

The superior physical properties of diamond with particular reference to its superior thermal conductivity, exceptional mechanical properties and

Table 1. Diamond Physical Properties




Chemical Reactivity

Extremely Low

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