Investigating possible crystal effects in ion scattering from elemental surfaces, measurements of the positive ion fraction $P^{+}$ are reported for ${\mathrm{He}}^{+}$ ions scattered from single and polycrystalline Cu surfaces. In the Auger neutralization regime, the ion yield is determined by scattering from the outermost atomic layer. For Cu(110) $P^{+}$ exceeds that for polycrystalline Cu by up to a factor of 2.5, thus exhibiting a strong crystal effect. It is much less pronounced at higher energies, i.e., in the reionization regime. However, there a completely different angular dependence of the ion yield is observed for poly- and single crystals, due to massive subsurface contributions in nonchanneling directions.

• Received 26 March 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.213201