Projectile survival during H^- and H collisions with Cu surfaces

Survival probabilities for H^- and H projectiles scattered from Cu(111) and Cu(100) surfaces are reported for energies ranging from 0.5 keV to 5 keV, and exit angles ranging from 20^o to 90^o. The projectile energy, exit angle, distance of closest approach to surface, and especially the metal band structure are important factors that influence the survival. Also, scattering on different faces of Cu yields different results, thus revealing a strong crystal effect on the ion/neutral fractions. At low perpendicular energies, the H^- survival on Cu(100) is smaller than on Cu(111), and continues to decrease as the energy decreases. For higher energies, the H^- survival on Cu(100) becomes higher than on Cu(111). For very fast collisions, the incoming projectile does not feel the band structure anymore, the copper surface behaves like a jellium, and the survival on both Cu(100) and Cu(111) is the same. The H survival on Cu(100) seems to be energy independent. On the contrary, the H survival on Cu(111) is both energy and angle dependent, and it is smaller. The study of PDOS shows that strong atom-surface interactions at short distances and the role played by the surface state are important factors in determining the neutral fractions after scattering.