Relevant effects of localized atomic interactions and surface density of states on charge transfer in ion-surface collisions

F. BONETTO; M. ROMERO; EVELINA A. GARCÍA; R. VIDAL; J. FERRÓN; E. C. GOLDBERG

EUROPHYSICS LETTERS

EPL

Año: 2007 vol. 80 p. 530021 - 530027

0295-5075

Ion scattering spectrometry with time of flight analysis is employed to measure the ion fraction of hydrogen positively charged (H+) projectiles scattered from a well characterized Highly Oriented Pyrolitc Graphite (HOPG) surface at a 45o scattering angle. The ion fraction is determined for several incident energies and exit angles. In the theoretical approach, the adsorbate-substrate interacting system is adequately described by means of an Anderson like Hamiltonian in which the coupling   terms are completely determined from the localized atom-atom interactions and the local density of states of the unperturbed surface. Under the previous assumption of a rapid neutralization of H+ projectiles (mainly related with a resonant electron capture), the negative ionization probability is calculated by employing a Green´s function formalism to solve the dynamic collision process. It is found a very good agreement between theory and experiment. The energy and angle dependence of the high ion fractions we found are understood by taking into account the combined effect of the semimetal character of graphite and the localized nature of the carbon atom states.