Crystal growth of CVD diamond and some of its peculiarities

Experiments demonstrate that CVD diamond can form in gas environments that are carbon undersaturated with respect to diamond. This fact is, among others, the most serious violation of principles of chemical thermodynamics. in this paper it is shown that none of the principles is broken when CVD diamond formation is considered not a physical process consisting in growth of crystals but a chemical process consisting in accretion of macro-molecules of polycyclic saturated hydrocarbons belonging to the family of organic compounds the smallest representatives of which are adamantane, diamantane, triamantane and so forth. Since the polymantane macro-molecules are in every respect identical with diamond single crystals with hydrogen-terminated surfaces, the accretion of polymantane macro-molecules is a process completely equivalent to the growth of diamond crystals. However, the accretion of macro-molecules must be described in a way different from that used to describe the growth of crystals because some thermodynamic functions are defined in manners different for solid phases (i.e. crystals) and for molecules. The CVD diamond formation is a chemical process proceeding on surfaces of polymantane seed macro-molecules (diamond seed crystals) under conditions under which the hydrogen-terminated surfaces exist but are chemically unstable. The process consists of several cyclically recurring consecutive reactions that can be thermodynamically coupled. The present approach makes it possible to predict correlations between the growth rate as well as the phase composition of deposited films and some important process variables. The predicted dependencies are perfectly consistent with experimental results.