PROBING SURFACES WITH IONS

Ions which carry potential and kinetic energy to a solid surface cause interactions through electronic and collisional processes. These occur with high probabilities and can be used to probe surface properties. The various mechanisms of electronic charge exchange and stopping have been explained on the basis of quantum mechanical concepts with varying degrees of sophistication; the growing understanding of the processes involved did not result in extensive exploitation of these processes for surface characterization. Interpretation of collisional processes is based on generally simple classical concepts and these processes became most important for probing surfaces with ions. Ion induced collision cascades lead to sputtering of surface atoms, a phenomenon which became extremely important for surface cleaning, depth profiling, surface characterization by analysis of sputtered particles and surface modification, e.g. due to radiation induced segregation. Analysis of backscattered ions in the low-energy (ion scattering spectroscopy) and high-energy (Rutherford backscattering spectroscopy) regime is a unique tool for the determination of surface compositions and structures. Some significant aspects of these developments over the last thirty years are discussed.