Direct evidence of Doppler shift in 10 keV Ar + ion induced Si Auger emission

Abstract

Angle resolved Si L-shell Auger emission induced by 10 keV Ar ion bombardment has been reinvestigated to study the spatial distribution of sputtered Si particles. We confirm all the major Si atomic-like Auger features whose kinetic energies are independent of either ion beam incidence angle or electron emission angle. We find, however, that at near-normal incidence the Si Auger spectra undergo characteristic lineshape changes showing the growth of satellites on the high kinetic energy side as the take-off angle moves away from the surface normal. The gradual splitting of the satellites from their main peaks results in a continuous transition of Auger features from singlets at normal emission to well separated doublets at grazing emission. The Auger peaks with fixed kinetic energies are due to the de-excitation of the sputtered slow Si species occuring outside the solid with a typical cosine distribution while the satellites at higher energies are atributed to the Doppler effects of the ejected fast Si particles in a narrow cone along grazing direction. The effect of the ion beam incidence angle on the higly anisotropic distribution of the sputtered energetic Si ions and neutrals is also discussed.