Absolute total cross sections for electron-stimulated desorption of hydrogen and deuterium from silicon(111) measured by second harmonic generation

Using second harmonic generation (SHG) as a sensitive measure of the amount of hydrogen or deuterium remaining on a silicon(111) surface, we have measured absolute total cross sections for electron stimulated desorption (ESD) over a range of incident energies from 50 to 300 eV. The measured cross sections for hydrogen are approximately a factor of 10 smaller than those found by Fuse [T. Fuse et al., Surf. Sci. 420, 81 (1999)] on the Si(100) surface and a factor of 10 greater than found for deuterium on the Si(111) surface by Matsunami [N. Matsunami et al., Surf. Sci. 192, 27 (1987)]. The measured cross sections for deuterium are consistent with the measurements of Matsunami et al. on the Si(111) surface. This indicates that while there is a significant isotope effect, the choice of surface also plays an important role. The details of the desorption spectrum are consistent with the multihole. desorption model. Comparison to calculated ionization cross sections suggests that the 2s core hole excitation is more likely to lead to desorption than the 2p core hole excitation.