Surface diffusion of oxygen on a Ge{100}(2 × 1) surface studied by laser-induced thermal desorption (LITD)

The capability of the laser-induced thermal desorption technique (LITD) to detect the migration of adsorbed oxygen on a semiconductor surface is demonstrated. The surface diffusion coefficient of oxygen on Ge{100}(2 × 1) has been measured for a constant initial coverage in a wide temperature range (220-650 K). The experimental results show that after an initial stage of fast refilling of the depleted area the diffusion process strongly slows down. In the first stage the data can be fitted by the solution of Fick's second law. Within this approximation of a constant diffusion coefficient, an extremely low activation energy (∼0.04 eV) is obtained. The observations suggest that the second stage in the refilling process is connected with an irreversible chemical reaction between adsorbate and substrate.