Ionization of Rydberg H2 molecules at doped silicon surfaces.

The present study focuses on the interaction of H2 Rydberg molecules with doped silicon semiconductor surfaces. Para-H2 Rydberg states with principal quantum numbers n = 17-21 and core rotational quantum number N(+) = 2 are populated via resonant two-colour two-photon (vacuum ultraviolet-ultraviolet) excitation and collide at grazing incidence with a surface. For small Rydberg-surface separation, the Rydberg states are ionized due to the attractive surface potential experienced by the Rydberg electron and the remaining ion-core is detectable by applying a sufficiently strong external electric field. It is found that the surface ionization profiles (ion signal vs applied field) of H2 on p-type doped Si surfaces show a higher detected ion signal than for n-type Si surfaces, while an Au surface shows lower detected ion signal than either type of Si surface. It is shown that ion detectability decreases with increasing dopant density for both types of Si surfaces. Higher-n Rydberg states show higher ion detectability than lower-n Rydberg states but this variation becomes smaller when increasing the dopant density for both p- and n-type surfaces. Theoretical trajectory simulations were developed with a 2D surface potential model and using the over-the-barrier model for the ionization distance; the results help to explain the observed variations of the experimental surface ionization profiles with dopant density and type

Surface ionisation of molecular H₂ and atomic H Rydberg states at doped silicon surfaces

The detection of ions or electrons from the surface ionisation of molecular H2 and atomic H Rydberg states incident at doped Si surfaces is investigated experimentally to analyse the effect of the dopant charge distribution on the surface-ionisation processes. In both experimental studies, the molecular H2 and atomic H Rydberg states are generated via two-colour vacuum ultraviolet - ultraviolet (VUV-UV) resonant excitation. For H2, various Stark states of the N+ = 2, n = 17 manifold are populated in the presence of an electric field. The variation of the observed surface-ionisation signal with surface dopant concentration and type, shows similar characteristics for all the Stark states. A comparison is made between these ion-detected surface-ionisation profiles and those obtained via electron detection. Different trends as a function of dopant concentration and type are observed for the two cases, explained by the greater effect of surface charges on the post-ionisation ion trajectory compared to the electron trajectory. For the atomic-H Rydberg states with principal quantum number populated in the absence of a Stark field, the observed behaviour is similar to the interaction of molecular H2 Rydberg states at the same surfaces, and these measurements confirm that the observed effects are attributable to the nature of the target surface rather than the specific atomic or molecular Rydberg species

Surface ionisation of molecular H-2 and atomic H Rydberg states at doped silicon surfaces

The detection of ions or electrons from the surface ionisation of molecular H2 and atomic H Rydberg states incident at doped Si surfaces is investigated experimentally to analyse the effect of the dopant charge distribution on the surface-ionisation processes. In both experimental studies, the molecular H2 and atomic H Rydberg states are generated via two-colour vacuum ultraviolet--ultraviolet (VUV-UV) resonant excitation. For H2, various Stark states of the N+ = 2, n = 17 manifold are populated in the presence of an electric field. The variation of the observed surface-ionisation signal with surface dopant concentration and type, shows similar characteristics for all the Stark states. A comparison is made between these ion-detected surface-ionisation profiles and those obtained via electron detection. Different trends as a function of dopant concentration and type are observed for the two cases, explained by the greater effect of surface charges on the post-ionisation ion trajectory compared to the electron trajectory. For the atomic-H Rydberg states with principal quantum number (Formula presented.) populated in the absence of a Stark field, the observed behaviour is similar to the interaction of molecular H2 Rydberg states at the same surfaces, and these measurements confirm that the observed effects are attributable to the nature of the target surface rather than the specific atomic or molecular Rydberg species. © 2014 © 2014 Taylor and Francis