Secondary ion emission from clean and K-covered Ni surfaces near threshold impact energies

Clean and K-covered Ni surfaces are bombarded with low energy (10–500 eV) beams of He⁺, Ne⁺, Ar²⁺, and Kr⁺ ions, and the emitted ion yield is measured as a function of beam energy. The apparent threshold energies for K⁺ and Ni⁺ emission are proportional to the ionic binding energies of K⁺ and Ni⁺ to the Ni surface. From comparison of the ion and neutral yield curves, it is suggested that these ions are emitted via momentum transfer collisions similar to neutral sputtering.