Transformation of Graphite to Diamond at Low Pressures

It can be shown, however, that the formation of diamond from graphite under the conditions of typical diamond CVD processes is not in conflict with classical thermodynamics if the CVD process is looked at in some more detail [52 and refs, therein]. 

An inevitable first highly endothermic step in the CVD reaction is the dissociation of molecular hydrogen by the application of energy, for example by means of a heated filament, a flame or an electrical gas discharge, reaction (2). The gasification of graphite, reaction (3) on the other hand, is strongly favored thermodynamically  

Summarizing reactions (3) to (8), one obtains a thermodynamically strongly favored net reaction (9) for the graphite-to-diamond transformation, driven by the input of atomic hydrogen  

2 Reactive Species in Diamond Chemical Vapor Deposition, the Role of CH3 

Several gas-phase diagnostic studies have been performed especially on the hot-filament CVD process in an attempt to analyze the spatial distribution of stable and reactive species in the region between filament and substrate and to obtain information about the decisive steps in the diamond formation mechanism. One of the first quantitative investigations of this kind was performed by Celii et al. using tunable infrared-laser detection of methane, acetylene, ethylene and methyl [54,551. Aside from a considerable conversion of methane (starting concentration 8 X 10 cm ) to acetylene (2 x lO cm ) near the hot filament (tungsten, 2200°C), methyl radicals were found with a concentration of 2 x lO cm .  

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