1 - General Introduction

Abstract

The extreme hardness, high thermal conductivity, excellent infrared transparency, and remarkable semiconductor properties combine to make diamond one of the most technologically and scientifically valuable materials found in nature. However, natural diamond is rare and only obtainable as gem stones in small sizes and at great expense. The scarcity and high cost have motivated researchers to attempt to duplicate nature and synthesize diamond. At room temperature and atmospheric pressure, graphite is the stable crystalline form of carbon, with an enthalpy 2 kJ mol-1 lower than diamond. Diamond is thermodynamically stable relative to graphite only at high pressures. The first breakthrough came in 1953 when H. Liander developed a high-pressure high temperature (HPHT) process using a liquid metal solvent-catalyst at pressures and temperatures where diamond is thermodynamically stable. The second breakthrough came with the discovery by W. G. Eversole of the Union Carbide Corporation in the U.S. that diamond could be deposited on a substrate from a hydrocarbon gas or a CO/CO2, mixture by chemical vapor deposition (CVD) at low pressures and temperatures where diamond is metastable with respect to graphite. The effects of surface conditions and deposition parameters on surface nucleation are also described.