Interactions of hydrogen and methyl radicals with diamond C(111) studied by sum-frequency vibrational spectroscopy

Abstract

Methyl-radical and atomic hydrogen adsorption on C(111) have been studied by infrared-visible sum-frequency vibrational spectroscopy. Methyl iodide, di-tert-butyl-peroxide, and methane passing through a hot filament are used to produce methyl radicals (${\mathrm{CH}}_{3}$). Low-energy ${\mathrm{CH}}_{3}$ from pyrolytic dissociation at \ensuremath{\sim}800 \ifmmode^\circ\else\textdegree\fi{}C adsorb intact on the surface, but with surface annealing above 350 \ifmmode^\circ\else\textdegree\fi{}C, convert to tetrahedrally bonded CH. High-energy ${\mathrm{CH}}_{3}$ produced at \ensuremath{\sim}1800 \ifmmode^\circ\else\textdegree\fi{}C convert readily to CH upon adsorption. Co-dosing a high-temperature (\ensuremath{\sim}800 \ifmmode^\circ\else\textdegree\fi{}C) C(111) substrate with hydrogen and methane via a hot filament at \ensuremath{\sim}1800 \ifmmode^\circ\else\textdegree\fi{}C yields only the stable tetrahedrally-bonded CH-species on the surface. They appear to stabilize the diamond surface structure. The coverage is not full, leaving sites open for ${\mathrm{CH}}_{3}$ to adsorb and convert to CH as is necessary for chemical vapor deposition diamond growth. \textcopyright{} 1996 The American Physical Society.