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

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 ∼800 °C adsorb intact on the surface, but with surface annealing above 350 °C, convert to tetrahedrally bonded CH. High-energy ${\mathrm{CH}}_3$ produced at ∼1800 °C convert readily to CH upon adsorption. Co-dosing a high-temperature (∼800 °C) C(111) substrate with hydrogen and methane via a hot filament at ∼1800 °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. © 1996 The American Physical Society.