Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 24: Methods: Molecular simulations and statistical mechanics

O 24.2: Talk

Tuesday, March 24, 2009, 15:15–15:30, SCH A01

First-principles study of the vibrational relaxation of the H stretching on Ge(100): Isotope effects — •Sung Sakong and Peter Kratzer — Fachbereich Physik, Universität Duisburg-Essen, Duisburg, Germany

The vibrational energy of covalently bonded adsorbates is dissipated to several smaller energy quanta (adsorbate vibrations and phonons) on semiconductor surfaces, when the vibrational energy is smaller than the gap. Then, electronic dissipation is precluded and the relaxation proceeds through slower channels of the coupling between vibrations and vibration-phonon interaction. Within the weak vibration-phonon coupling regime, this slow relaxation process can be described by the first-order perturbation theory using a potential energy surface obtained from first-principles calculations (J. Chem. Phys. 129, 174702 (2008)). Using this framework, we analyze the vibrational relaxation of the H-Ge stretching on Ge(100) surface. Because of the small energy of Ge phonons, the downward transitions from the H stretch mode require at least two phonons to satisfy energy conservation. Most interestingly, the relaxation of the H stretching becomes up to five times faster at a heterogeneously saturated dimer using H and D, as observed in SFG experiments. The weak interaction between H and D within a dimer opens relaxation channels that require only one phonon for the transition instead of two phonons. Transitions mediated by fewer phonons corresponds to lower order expansion terms of the vibrational potential, thus these channels systematically make a larger contributions to the relaxation process and lead to a faster vibrational lifetime.