Mass-resolved low-energy back-scattering of alkali ions

The emission charge state dependence of alkali metal ions back-scattered in binary collisions has been evaluated. For this purpose, mass-resolved LEIS in an SIMS instrument was utilized during bombardment of 133Cs+ or 39K+ on metal surfaces (Ta, Au or Cu) under dynamic sputtering conditions. Back-scattered singly positively charged alkali ions were found to be by far predominant (i.e. with an at least a factor of 1000 larger flux than other ejected alkali ions). Back-scattered negative alkali ions (133Cs−, 39K−) as well as doubly positively charged alkali ions (133Cs++, 39K++) were also observed, while other emission charge states (such as triply positively charged alkali ions) could not be detected.