Elastic and inelastic processes in the interaction of 1–10 eV ions with solids: ion transport through surface layers

We review the escape depth of secondary ions (or neutrals) desorbing from solid surfaces under the impact of electrons, photons or ions. We survey ion (or neutral) transport through many materials, but most are wide band gap insulators such as rare-gas solids and molecular solids. We address the issue of low-energy (<10 eV) ion—solid interactions, and review experimental and theoretical studies that provide insight into the physical mechanisms of these interactions, such as elastic scattering, charge transfer and ion—molecule reactions. Although it is usually assumed that most of the secondary ions stem from the top surface layer, we show that this is not necessarily the case: In certain instances, 1–10 eV ions are able to transmit solid films which are several monolayers thick. The transport of low-energy ions through materials has very broad implications. We point out the importance of these results for electron or photon stimulated desorption (ESD/PSD), secondary ion mass spectrometry (SIMS), and ion-sputtering of surfaces, and discuss their relevance to other fields, such as ion beam deposition (IBD), low-energy ion implantation, and electrochemistry.