ATOMIC AND ELECTRONIC-STRUCTURE OF THE DIAMOND(100) SURFACE - RECONSTRUCTIONS AND REARRANGEMENTS AT HIGH HYDROGEN COVERAGE

The atomic and electronic structure of the diamond (100) surface has b een investigated theoretically via a semiempirical tight-binding model for a range of hydrogen coverages. Model parameters for C-C interacti ons have been taken from the work of Goodwin [J. Phys. Condens. Matter 3, 3869 (1993)], while new parameter sets have been determined for C- H and H-H interactions. The model gives results for the clean and mono hydrogenated surfaces in good agreement with previous studies, but dif ferent features have been identified for higher H coverages. When the H coverage is sufficiently high, the substrate lattice is found to dis tort in order to reduce steric repulsions between dihydride units. As an important example, we obtain two structures for the dihydrogenated surface that are significantly more stable than those proposed previou sly. For H coverages intermediate between the monohydrogenated and dih ydrogenated surfaces, stable geometries consisting of monohydrogenated dimer units and dihydride units are found. In contrast, geometries th at include isolated monohydride units, such as have been previously in vestigated, are found to be thermodynamically and kinetically unstable . Tight-binding molecular dynamics is used to illustrate a mechanism f or the rapid removal of isolated monohydride units. The electronic str uctures of the surfaces are described via the total and partial electr onic densities of state, which are obtained directly from the tight-bi nding Hamiltonian. For the monohydrogenated surface and higher coverag es, the stable geometries are found to yield no states in the bulk ban d gap.