Secondary ion production due to ion-surface bombardment

Abstract

In this paper secondary ion production due to ion-surface bombardment is reviewed. Special emphasis is given to a discussion of experimental data which can be used to check the validity of certain emission models. For clean metals bombarded with rare gas ions in the keV energy range the dominant processes leading to the emission of positive ions are autoionization and (for light elements) kinetic ionization, the latter phenomenon involving 1s or 2p hole production. Analysis of secondary electron spectra indicates a high probability for interaction between Auger electrons and sputtered particles. Accordingly ionization due to Auger electron impact is likely to be important in some cases. Secondary ion emission in the presence of electropositive and/or electronegative elements is discussed in some detail. The enhancement in the positive ion yield due to the presence of oxygen supports the bond breaking model. Different from photoemission studies the experimental results cannot be explained on the basis of band structure considerations. The yield of negative metal ions is found to be strongly related to the electron affinity. The yield of clusters, both homonuclear and heteronuclear, exhibits a strong dependence upon the bond strength. Bombardment induced changes in surface structure and stochiometry are shown to be of pronounced importance. The role of recoil implantation in producing saturation with oxygen is emphasized. The possibility of achieving substrate-independent secondary ion emission pattern from oxygen saturated surfaces is pointed out. Finally it is demonstrated that the current state of the theories of secondary ion emission is unsatisfactory.