Photon-emission induced by impact of fast ions on metal surfaces

Abstract

A study has been made of photon-emission induced by impact of H⁺ and He⁺ isns on gold and nickel metallic surfaces. An energy selected ion beam (3 to 10 keV) is directed onto a metal surface and the emitted light is analyzed by a monochromator (3000-4000 Å). The target is located in a vacuum chamber with base pressure of 1 × 10⁻⁹ torr, the target is cleaned by heating and by Ar⁺ -sputtering. Lines from the He-spectrum (3³D, 4³D, 5³D → 2³P and 3³P → 2³S) and H-spectrum (Balmer α, β, γ) are observed for impact of He⁺ and H⁺ respectively on both targets. No singlet lines of helium were observed and also no line emissions from the target material. The line-shape of the He-lines has been studied in detail. The shape can be qualitatively explained by Doppler shifts of emission from projectiles scattered by bi-particle collisions in the surface. The total intensity of the lines increases as a function of beam energy and of incidence angle on the surface.