4.1 Introduction

Diamond is becoming an increasingly important material in the recent decades. The unique predominance of diamond that brings together both excellent physical and chemical properties shows its promise for applications in many areas. However, the rarity and the high cost of natural diamond have severely limited its applications and thus has stimulated scientists to search for methods to synthesize diamonds.

The first successful synthesis of diamond was reported by Bundy and co-workers (1962) [1]. They used the high pressure and high temperature (HPHT) technique in which diamond was prepared at 8 GPa pressure and 1500 K, and graphite was the source of carbon and Fe, Ni, and Co were used as catalyzers. After that the HPHT technique was developed by many researchers. Until now diamond for industrial consumption has been produced mainly from the HPHT synthesis method.

Other synthesis methods of diamond were also found. It's known that the hydrothermal process may be responsible for most natural diamonds. Using this idea, diamond from metal-carbon solution was reported in 1990 and there is now a revival of interest in synthesizing diamonds hydrothermally in the laboratory [2].

Owing to the cost of production and the small size, applications of diamond prepared by the above techniques were always limited, unlike those of natural diamond. Diamond film formation under relatively low pressure and temperature...