Ionization of xenon Rydberg atoms at oxidized Si(1Â 0Â 0) surfaces

The ionization of xenon Rydberg atoms excited to the lowest states in the n = 20 Stark manifold at Si(1 0 0) surfaces possessing a robust (∼10 Å) native oxide layer is investigated. The data show that a sizeable fraction of the incident atoms are ionized relatively far from the surface through enhanced tunneling due to the presence of localized stray fields at the surface associated with surface charging or with surface inhomogeneities. A simple model is presented to justify this assertion.