Chemistry of hydrogen on diamond (100)

Abstract

Hydrogen plays a crucial role in diamond film growth by chemical vapor deposition and is likely to be similarly critical to atomic layer epitaxy, yet the surface chemistry of hydrogen on diamond is only beginning to be understood. We investigated the adsorption of hydrogen and deuterium on diamond (100) by temperature-programmed desorption and by IR multiple-internal-reflection spectroscopy using a natural type IIa diamond internal reflection element. Complementary theoretical studies were carried out using the empirical MM3 molecular mechanics force field, which has a demonstrated high degree of accuracy for many molecules despite computational simplicity. H 2 desorption was observed with a peak temperature of approximately 1250 K and a peak shape suggestive of first-order kinetics, and is assigned to the monohydride surface structure, with one hydrogen atom per surface carbon atom. Assuming a pre-exponential factor of 10 13 s −1, the activation energy for desorption is estimated as approximately 80 kcal/mol -1. IR evidence was seen for the monohydride surface structure, with one hydrogen atom per surface carbon atom (δ CD mode at 901 cm −1), for the first time on diamond (100). The MM3 calculations predict that the (2 × 1):H monohydride phase is the most stable thermodynamically and the dominant phase under typical chemical vapor deposition conditions.