Angle-resolved fast atom scattering: He on clean Cu{111}

Abstract

The scattering of fast (250–1000 eV) He atoms from a clean Cu{111} surface, along the 〈1 1 0〉 and 〈2 1 1 〉, 〈1 2 1〉 azimuths has been studied. For 50° incident angle along the 〈1 1 0〉 azimuth, up to three peaks are seen, all of which show a polar angle which changes with beam energy. They comprise a rainbow peak occurring at polar angles between 64° and 68.5° for beam energies 250–1000 eV and an additional peak set at the surface normal, which splits into peaks at 8° and −8° at 1000 eV. Beams incident along the 〈1 2 1〉 azimuth give a rainbow peak at 73.5° to 76° and peaks at ~0° and ~55°. The latter peaks grow in magnitude and move to larger polar angles with increasing beam energy. For the 〈2 1 1 〉 azimuth three peaks are seen, a rainbow peak positioned as for the 〈1 2 1〉 azimuth and peaks at ~0° and ~35° which grow and move to slightly smaller polar angle with increasing beam energy. These peaks are attributed to scattering from 2nd and 3rd layer atoms. The polar angle of the rainbow peak, for a given azimuth and energy, grows with increasing angle of incidence changing from 64° to 68.5° (〈1 1 0〉) and from 72° to 75° (〈1 2 1〉, 〈2 1 1 〉) for angles of incidence from 20° to 60°: it is markedly sensitive to the surface atom spacing. Computer simulation of the rainbow peak scattering has been carried out using a Born-Mayer repulsive potential V( R) = A exp(− bR); and found to fit with A = 1805 eV, b = 4.17 A ̊ −1 .