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 ϳ5 eV, the desorption yields for H and D are temperature independent, while in the tunneling regime, below 4 eV, H is a factor of ϳ300 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. [S0031-9007(97)

A cryogenic variable temperature ultrahigh vacuum (UHV) scanning tunneling microscope (STM) has been developed. This design utilizes a novel vibration isolation that provides an active thermal link to the cooling source without the standard tradeoff of compromising mechanical isolation. A welded bellows serves as the basis for the vibration isolation system. This bellows houses a heat exchanger which uses helium gas to form a thermal link between the STM and the cryogenic. This STM is fully integrated into a multichamber UHV STM system now in place in our laboratory and atomic resolution operation is demonstrated from 11 to 300 K.