Time-domain investigation of laser-induced diffusion of CO on a vicinal Pt(111) surface

Abstract

We report on a time-domain study of diffusion of CO on a vicinal Pt(111) surface at low substrate temperature induced electronically via substrate electrons, which have been optically excited by femtosecond-laser pulses. Hopping rates from step sites to terrace sites have been determined using optical second-harmonic generation as a sensitive probe of the step coverage. The dynamics of the electronic energy transfer between the excited substrate electrons and the adsorbate degrees of freedom have been investigated by the application of a two-pulse correlation scheme. We observe a nonlinear dependence of the hopping rate on the laser fluence $(\ensuremath{\propto}{F}^{6})$ in a fluence range of $F=1.9--4.3\text{ }\text{mJ}/{\text{cm}}^{2}$ and a narrow two-pulse correlation with a width of below 0.5 ps that increases with increasing laser fluence. It will be shown that the broadening of the two-pulse correlation with laser fluence is a general phenomenon for substrate mediated laser-induced surface reactions.