Optical Radiation from He Particles Scattered at a Monocrystalline Surface at Grazing Incidence

Abstract

In detailed investigations, the scattering and the interaction mechanisms of 70 to 200 keV He+ ions at grazing incidence on a monocrystalline (110) NiFe surface are studied both by experiments and by computer simulations. The light intensity I and the Stokes parameters S/I, C/I, and M/I of the He+–468.6 nm and of the He0–587.6 nm radiation emitted by the scattered particles were observed as function of the angles of incidence relative to surface lattice directions and of the cleanness of the surface. The results exhibit a strong dependence of I and S/I on the surface crystallography and coverage. An interpretation of the results is proposed on the basis of two excitation mechanisms, (i) excitation by electron capture from the metal surface, (ii) excitation by collisions with adsorbed atoms, and (iii) an Auger deexcitation or resonance ionization mechanism which quenches the light emission of particles with small scattering angles.