The energy relaxation of Si-H vibration in the H/Si(111) system. Relaxation rate and potential energy surface anharmonicity

The vibrational energy relaxation of the Si-H stretching vibration in the H/Si(111) system is investigated by application of the perturbation theory to the anharmonic Si-H oscillator. The eigenfunctions for the 3D motion of an adsorbed H atom are obtained with an ab initio potential energy surface calculated for the H-Si(SiH3)(3) cluster. The transition matrix elements between the vibrational states involved in the relaxation process are evaluated. The spectrum of the velocity autocorrelation function of the top Si atom appearing in the expression for the relaxation rate is calculated with classical molecular dynamics and corrected for the quantum effects. The energy relaxation channels are indicated and the calculated relaxation rates are compared with experimental data. The calculated slow decay of the H atom excitation is clue to a small value of the transition matrix elements. The magnitudes of these matrix elements are shown to be sensitive to the high-order anharmonicity parameters of the potential energy surface. (C) 1998 Elsevier Science B.V. All rights reserved.