J.E. Gayone

Adsorption kinetics and surface unrelaxation in H:GaAs(110) studied by time-of-flight scattering and recoiling spectrometry

Time-of-flight scattering and recoiling spectrometry is used to study the chemisorption of H on a GaAs(110) surface. Monitoring of the neutral plus ion intensity for both the H direct recoils and the Ne and Ar backscattered projectiles as a function of the H exposure, the surface temperature, and the incident direction of the projectiles gives information about the substrate unrelaxation and its dependence on the adsorption kinetics. It is found that the adsorption proceeds with a sticking coefficient that decreases strongly with the coverage. At low exposures, the unrelaxed fraction of the surface increases linearly with the coverage. For coverages of the order of one monolayer there is an important fraction of the surface that remains relaxed as in the clean surface. The H recoil intensity is almost independent of the crystallographic sample orientation, suggesting that an important fraction of the H atoms are not adsorbed in well ordered sites.

Adsorption of potassium on GaAs(110)

The adsorption of potassium on the GaAs(110) surface has been studied by ion scattering and recoiling spectroscopy (SARS) and Auger electron spectroscopy (AES). The SARS measurements indicate that a major part of the potassium atoms adsorb along the [001] gallium rows, in a region close to the sites of a new arsenic layer, and that only a minor part of the potassium atoms adsorb along the [001] arsenic rows. In agreement with this suggestion, the energy shifts in the substrate Auger peaks indicate that, at the beginning of the adsorption, the potassium atoms react preferentially with gallium atoms.

TOF-ISS investigation of the dependence of the GaAs(110) surface derelaxation with the hydrogen exposure

Abstract We have used ion scattering spectrometry with time of flight analysis to investigate the atomic structure of a GaAs(110) surface exposed to atomic hydrogen. The backscattering intensity resulting from 6 keV Ne + ion-surface collisions changes with the H exposure. The changes are consistent with derelaxation towards a bulk terminated surface. The derelaxation processes present a very strong dependence upon H exposure until approximately one half of the surface has been derelaxed. At large exposures the Ne backscattering features reach a steady stage indicating that 90% of the surface has been derelaxed.

Ion fractions in 6 keV Ne+, Ar+ and Na+ scattering from a GaAs(110) surface

Abstract We used Ion Scattering Spectrometry (ISS) with Time-of-Flight (TOF) analysis to study the neutralization of 6 keV Ne+, Ar+ and Na+ backscattering from a flat and ordered GaAs(110) surface. At low incident angles an important contribution to the total (neutral + ion) backscattering spectra comes from quasi single collisions with As and Ga first layer surface atoms. We observed that the ion fraction in this contribution is strongly dependent on both the incident projectile and the target atom, suggesting that the violent collision plays an important role in the neutralization process. In order to interpret these dependencies we performed a calculation that discriminates the interaction of the projectile with the extended and localized states of the solid.