Radiation damage during surface analysis

Abstract

During surface analysis of solids by means of secondary ion mass spectrometry (SIMS), ion scattering spectrometry (ISS), Auger electron spectroscopy (AES) and photoelectron spectroscopy (XPS or ESCA), excitation with ions, electrons and photons can result in radiation-induced damage. Artefacts of this kind are for example morphological changes due to sputtering, stoichiometric changes (reduction, formation of new compounds, selective accumulations), electron and ion-induced adsorption and desorption, charge-dependent diffusion and structural changes (crystallization, amorphisation). Detection of compounds when using ions for excitation (SIMS and ISS) or in sputtering of solids for recording depth profiles in conjunction with all surface analysis methods is particularly critical due to the high energy of the ions transmitted to the solid. In AES, problems arise because of the high electron current densities generally used. A number of characteristic examples are presented to demonstrate which critical radiation doses must not be exceeded in “static” or “low damage” surface analysis. Artefact-free analyses of the upper monolayers of solids are achievable with all surface analysis methods by choosing suitable measurement parameters. When recording ion bombardment depth profiles and in microanalysis with high lateral resolution with scanning Auger microscopy (SAM) and ion microscopy, radiation damage cannot be excluded.