ELASTIC-SCATTERING AND CHARGE-EXCHANGE IN HE+ ION-SCATTERING FROM ALKALI-METAL OVERLAYERS

Low energy (1 kev) He+ ion scattering data from clean Cu(110) reveal simple binary collision spectra expected from a surface which readily neutralizes the ions by an Auger process. Experiments with sodium, potassium and cesium overlayers show that scattering from these species leads to energy loss features characteristic of reionization by electron promotion; similar features in the copper scattering peak on alkali adsorption are thought to be due to inelastic losses in the overlayer. Sodium adsorption in particular also causes a high background of inelastically scattered ions to be observed, implying reionization of He+ ions which penetrate the copper substrate; the mechanism for this reionization is unclear.