Ion Fractions in the scattering of hydrogen on different reconstructed silicon surfaces

EVELINA A. GARCÍA; C. GONZÁLEZ PASCUAL; P. G. BOLCATTO; M. C. G. PASSEGGI; E. C. GOLDBERG

SURFACE SCIENCE

Elsevier B. V.

Lugar: Amsterdam, The Netherlands; Año: 2006 vol. 600 p. 2195 - 2206

0039-6028

A theoretical calculation that accounts for a fairly complete description of the reso-nant charge-exchange process occurring in H0 scattering by Si surfaces is presented.Two reconstructed surfaces for the target: Si(100)2x1 and Si(111)7x7, are an-alyzed in this work. The interacting system is described by an extended spin-lessAnderson Hamiltonian where valence as well as core states of the surface atoms areincluded. The interaction terms are calculated by taking into account the extendedfeatures of the surface and the localized atom-atom interactions within a mean-field approximation. The study is focused mainly in the description of the collisionprocess in terms of short range interactions. The density of states for the surfaceand sub-surface atoms are obtained in each case, from a molecular dynamic-densityfunctional theory in the local density approximation. A binary elastic collision isassumed to fix the projectile trajectory, while the inelastic processes are determinedby the interaction of the projectile atom with all the surface atoms ´seen´ along itstrajectory. The ion fractions are calculated by using the Keldysh-Green´s functionformalism to solve the time dependent process. We analyze the negative ion frac-tions of hydrogen measured by Maazouz et al. By including the interaction of theion projectile with the target atoms seen during its trajectory and averaging overa variety of scattering centers as it may occur in the experimental situation, weobtained a smooth dependence with the exit angle that does not reflect the specificdetails of the local density of states and the surface topography while reproducingvery well the general trends of the experiment. The ion fraction is found to be almostindependent on the incoming energy for large values of the exit angles, while in theopposite cases where the projectile spends longer times in contact with the surface,the effect of the parallel component of the velocity has an increasing importance.Thus, the fine details of the surface are ´better captured´ as the parallel velocitycomponent becomes smaller.