A cryogenic UHV scanning tunneling microscope has been used to study the electron stimulated desorption of hydrogen and deuterium from Si(100) surfaces at 11 K. A strong isotope effect is observed, as seen previously at room temperature. Above $\sim 5\mathrm{eV}$, the desorption yields for H and D are temperature independent, while in the tunneling regime, below 4 eV, H is a factor of $\sim 300$ easier to desorb at 11 than at 300 K. This large temperature dependence is explained by a model that involves multiple vibrational excitation and takes into account the increase of the Si-H(D) vibrational lifetime at low temperature.

• Received 19 June 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.1336