The Importance of the Positively Charged Surface for the Epitaxial Growth of Diamonds at Low Pressure

Abstract

The mechanism of the propagation of the epitaxial growth of diamonds at low pressure was investigated in terms of quantum chemistry. The reactions for diamond structure formation proceed simultaneously at many points on the surface of a diamond, and the epitaxial growth continues so long as methyl radicals are supplied. The most important requirement is the maintaining of positive charges on the growing surface.

Diamond growth by chemical vapour deposition

“…When the low reactivity of methane is taken into account, only CH 3 and C 2 H 2 are left as likely growth species under typical diamond CVD conditions. Several mechanisms for diamond CVD have been proposed, including CH 3 -based mechanisms [81,82], Acetylene-addition mechanisms [83], Combined CH 3 -C 2 H 2 mechanism [83].…”

Chemical Reaction Mechanisms of Diamond Growth

“…The mechanism suggested by Tsuda et al that implicated either gaseous methyl cations 3 7 or the presence of a positive charge on the surface, 38 faces two major difficulties. First, the critical role of ions or electrostatic charges has not been corroborated by experiment; and second, a prohibitively strong repulsion exists among methyl groups required to be adsorbed at three neighboring sites of the (111) surface.…”

Thermochemical and Kinetic Considerations in Diamond Growth

“…It also appears consistent with the experimental observation that diamond is not readily gasified by atomic hydrogen. Nevertheless it remains to be established that the rate controlling step is indeed reaction (2). Given the quantitative uncertainties in such estimates, it is quite possible that the apparent agreement with experiment is more fortuitous than real.…”

“…The difficulty with this is that the exchange reaction between H 2 and D 2 to form HD is known to be catalyzed, at temperatures too low for a gas phase radical chemistry, by an active diamond surface [48,49]. The dissociative chemisorption of H 2 , and thus its reverse process, the associative desorption of H 2 , D 2 or HD, is almost certainly required for this catalysis. Presumably the local symmetry at active sites on diamond is significantly different from that for simple gas phase hydrocarbons and thus constraints imposed for elementary reactions in the gas phase may not apply to the diamond surface.…”

“…Numerous models have been offered to rationalize the growth of diamond with some focusing on various charged species [1][2][3], others suggesting acetylene as the dominant growth species [4][5][6], and still others focusing on various reactive radicals, ranging from atomic carbon [7] to the methyl radical [8][9][10][11][12]. The suggestion that neutral radical chemistry plays an important role has a long history, beginning with the early suggestion by Eversole [8] that "...either methane or compounds that decompose to methane or methyl radicals are needed."…”