Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 30: Phenomena at Semiconductor Surfaces

O 30.1: Talk

Tuesday, February 26, 2008, 12:00–12:15, MA 041

Vibrational relaxation of CO stretching excitation on Si(100): DFT study — •Sung Sakong and Peter Kratzer — Fachbereich Physik, Universität Duisburg-Essen, Duisburg, Germany

On semiconductor and insulator surfaces, the vibrational lifetime of adsorbates can be very long and the vibrational energy is predominantly dissipated to phonons, because electron-hole pair excitations are not allowed. Recently, the lifetime of the CO stretch vibration on Si(100) has been measured to be 2.3 nano seconds (Laß et al., J. Chem. Phys. 123 051102 (2005)).

We have performed density functional theory calculations within the framework of the generalized gradient approximation for the energy dissipation of the CO vibrational mode on the Si(100) surface. In this scheme, the vibrational relaxation is controlled by the anharmonic coupling between vibrational modes and the interaction between vibrations and phonons. In DFT, vibrational excitations of the adsorbate are accurately described by the multi-dimensional potential energy surface which includes anharmonic coupling between vibrations. And the phonon properties of the underlying Si substrate are calculated with the force field method to treat a large slab. From this information, the coupling between anharmonic vibrations and the phonon continuum is calculated within perturbation theory, thus the transition rate is derived by Fermi’s Golden Rule. The calculated lifetime is in qualitative agreement with the experiments and the suggested microscopic decay channels of the stretching mode of C-O into lateral shift/bending quanta and a phonon satisfy energy conservation.