TOF-ISS study of clean and absorbate covered GaAs(110) surfaces. Atomic structure characterization and charge exchange

J. E. GAYONE; E. A. SÁNCHEZ; O. GRIZZI; L. VERGARA; R. VIDAL; M. C. G. PASSEGGI(JR),; J. FERRÓN; E. GOLDBERG

Paris, Francia

Conferencia; 19th International Conference on the Physics of Atomic Collisions in Solids (ICACS-19); 2001

Universidad de Paris

TOF-ISS study of clean and adsorbate covered GaAs(110) surfaces. Atomic structure characterisation and charge exchange   J.E. Gayone1, E.A. Sánchez1, O. Grizzi1, L. Vergara2, R. Vidal2, M.C.G. Passeggi (Jr)2, J. Ferrón2 and E. Goldberg2.     1- Centro Atómico Bariloche and CONICET, 8400 Bariloche, Argentina. 2- INTEC (UNL-CONICET), GŸemes 3450, CC91, 3000 Santa Fe, Argentina.                   We used ion scattering and recoiling spectroscopy with time of flight analysis (TOF-ISS) to characterize the elemental composition and the atomic structure of GaAs (110) surfaces covered with different adsorbate layers, i.e.: H, K, Cs, O on K:GaAs, and insulating layers (AlF3). For these systems we studied the ion fractions in the scattered projectiles (Ne, Ar at keV energies), and in the recoiling target atoms (Ga, As, H, K, O, Al and F).                   Comparison of shadow cone calculations with backscattering and recoiling intensities measured as a function of projectile incident angle and sample orientation indicate that the clean surface relaxation is removed upon adsorption of H or K.  The recoiling intensities for all the adsorbates measured at doses close to one monolayer present weak variations with the sample azimuthal orientation, suggesting that the adsorption sites are not well ordered. Measurements as a function of the dose indicate that at low exposures K is preferentially adsorbed near Ga atoms. Oxygen adsorption is very slow on the clean surface, but is strongly enhanced (promoted) by small amounts of K. At low K coverages O atoms are preferentially on As [001] rows. The AlF3 films are stoichiometric and disordered when the evaporation is performed at room temperature and present some ordering for post-annealed films.                   The atomic structure characterization allowed us to study the ion fractions of scattered and recoiled particles in well defined incident conditions; for example, with focussing of scattered or recoiling intensities on a particular layer (Ga, As, or adsorbate) and with reduction (or enhancement) of second layer contributions. An interesting aspect of the GaAs surface is that since the masses are similar, the velocity effects on the scattering and recoiling ion fractions are similar. The different behavior observed in the ion fractions can be related to the local electronic structure. The results show that the ion fractions in the scattered projectiles are strongly dependent on both the incident and target particles, while the ion fractions in the recoiling atoms are less dependent on the impinging particle and are more sensitive to the surface electronic structure. Dependences of the ion fractions on exposure and correlation between ion fractions and adsorbate sites will be discussed.