Experimental and theoretical study of Hydrogen scattering from a graphite surface

F. BONETTO; E. A. GARCIA; R. VIDAL; J. FERRÓN; E. GOLDBERG

Bariloche, Rio Negro, Argentina

Conferencia; 13º International Conference on Solid Films and Surfaces (ICSFS 13); 2006

Centro Atómico Bariloche, Instituto Balseiro

The efforts made in trying to understand how Hydrogen interacts with solids are based, besides its intrinsic basic interest, on its importance as a clean and renewable source of energy. The energy range of interest is, on the other hand, extremely wide going from the static one in the H storage devices, up to thousands of keV in the fusion reactors.  Within this last case, the interaction of energetic H with C seems to be the most interesting combination since graphite is considered the first choice as wall material in magnetically confined fusion devices. In the present work, we perform both theoretical and experimental studies of the ion formation during positive H ion scattering on Highly Oriented Pyrolitc Graphite (HOPG), for a wide range of incoming energies and incident and outgoing angles.  Ion scattering spectrometry with time of flight analysis is employed to measure the ion fraction in H+ projectiles scattered from a well characterized HOPG surface at two fixed scattering angles: 45o and 135o. For both scattering angles and after analyzing the time of flight spectra, the ion fraction is determined for several incident energies (in the low keV range) and outgoing angles. In the theoretical approach, the adsorbate-substrate interacting system is adequately described by means of an Anderson like Hamiltonian where the valence and core surface states are included. Under the previous assumption of a rapid neutralization of H+ projectiles (mainly related with a resonant electron capture), the positive and negative ionization probabilities can be calculated by employing a Green´s function formalism to solve the dynamic collisional process. Both theoretical and experimental results are analyzed and contrasted for a fixed set of parameters: incident energy, scattering and outgoing angles. The dependence of the scattered ion fractions with these parameters, and the effect of the semi-metal character of Graphite (HOPG) in the negative ion formation, are specially analyzed.