Effect of the projected band gap on the formation of negative ions in grazing collisions from Cu surfaces

The formation of negative ions (H-, O-, S-, F-, Cl-) is studied for grazing scattering of fast ions from Cu(110) and Cu(111) surfaces. In a detailed experimental and theoretical investigation we reveal that the projected L-band gap of the Cu metal affects charge transfer in a specific manner. From the analysis of the negative ion fractions as functions of projectile velocity we conclude that, for the Cu(111) surface the electronic 2D surface state continuum plays an essential role in the projectile-surface electron transfer.