Theory of the charged cluster formation in the low pressure synthesis of diamond: Part I. Charge-induced nucleation

Based on several experimental observations, Hwang ef al. recently proposed "the charged cluster model" [J. Cryst, Growth, 162, 55-68 (1996)] to disentangle the "puzzling thermodynamic paradox" encountered in the gas-activated chemical vapor deposition (CVD) of diamond. Many unusual phenomena observed in the CVD diamond process can be successfully approached by the charged cluster model. However, there are a couple of important subjects still unsolved quantitatively, The first question is connected with the main driving force for this unusual nucleation in the gas phase. The second issue is related to the difference in the thermodynamic stability between graphite and diamond for a nanometer-sized cluster during the growth. In this study, we have theoretically examined the thermodynamic driving forces for the charge-induced nucleation, in general, and have applied this idea to the nucleation of the charged carbon-atom cluster. It was shown that the short-range ion-induced dipole interaction and the ion-solvation electrostatic effect (Born term) were mainly responsible for this unusual nucleation in the gas phase. The theoretical analysis presented in this article is quite generic and, thus, can be applied to any process that involves the charge-induced nucleation.