ABINITIO STUDIES OF H CHEMISORPTION ON SI(100)

Ab initio configuration-interaction theory is used to study the chemisorption of hydrogen on the Si(100)2 X 1 reconstructed surface in the monohydride and dihydride phases. A three-layer cluster, that consists of 12 silicon atoms and 20 hydrogen saturators is used to simulate the major features of surface reconstruction. The chemisorption of H atoms changes the surface reconstruction slightly in the monohydride phase, shifting the dimer length from 2.401 angstrom in a H-free surface to 2.466 and 2.472 angstrom for a dimer bonded with one and two H atoms, respectively. The Si-H bond energy is calculated to be 3.50 eV for the chemisorption of the first H atom and 3.58 eV for the chemisorption of the second H atom, including the zero-point vibrational energy. The Si-H stretch frequency is computed to be 2099 cm-1. In forming the dihydride phase, the chemisorption of H atoms destroys surface dimers and changes the reconstructed 2 X 1 surface to the unreconstructed 1 X 1 surface. The interactions between surface SiH2 groups are found to be repulsive. The desorption of H-2 from the monohydride and dihydride phases is also discussed.