Diamond surfaces : interactions with hydrogen and halogens

Citation

Melnik, M. Susan (1997) Diamond surfaces : interactions with hydrogen and halogens. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/gdrt-7n92. https://resolver.caltech.edu/CaltechETD:etd-01162008-075117

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Absolute deuterium coverage on the diamond C(100) surface has been measured under a variety of dosing conditions by nuclear reaction analysis (NRA) using [...]. The (2x1) surface with ~1.0 D per surface C is produced under typical dosing conditions. However, at unusually high filament temperatures circa 2000°C, coverages up to 1.34 ± 0.09 D per surface C are observed. Coverage is calibrated by comparing to a standard containing 1.5x[...] D/[...]. Signal from subsurface deuterium is estimated to be negligible by comparison to previous scattering experiments and by secondary-ion mass spectroscopy of a homoepitaxial CVD (100) sample. D breakage of surface dimer bonds at high filament temperature is proposed as a mechanism to generate surface dideuterides. The relevance of dimer breakage and dihydride formation to recent experiments on surface degradation is briefly discussed. Previous models of hydrogen reactions with C(100) are substantially revised to include all types of sites on the reconstructed terrace, and it is shown that saturation coverage determines the ratio of site-averaged abstraction rate to site-averaged recombination rate, [...]. NRA coverage measurements of 0.95 ± 0.04 D per surface C imply a [...] of 0.06 ± 0.04 at 1800°C gas temperature and 360°C surface temperature. Results indicate that thermochemical kinetic models overpredict by a factor of ~20 the fraction of sites available for growth during diamond CVD. In a separate issue, C(110) surface mobility is demonstrated by calculating activation energies for the migrations of H, F, and Cl with quantum chemical methods using hydrocarbon cluster models. The calculations included extensive basis sets with many-body effects at the level of single and double excitations from Hartree-Fock and Complete-Active-Space wavefunctions. Intra-chain migrations of H along [...] carbon chains and nearest-neighbor F migration are found to be too slow to compete with thermal desorption. However, inter-chain migrations of H and Cl are calculated to be sufficiently fast to compete with thermal desorption under ultrahigh vacuum conditions and with gas-surface reactions under typical diamond growth conditions. This was the first study to consider migration rates as well as barriers, establishing mobility's competitiveness during diamond growth. [...]/[...] is estimated to be [...]. Finally, a kinetic Monte-Carlo algorithm is presented to directly combine mobility with gas-surface reactions in the same iteration step when simulating hydrogen processing of diamond.

Thesis Files