Nanoscale Electron Beam Damage Studied by Atomic Force Microscopy

High-resolution scanning electron microscopy (HRSEM) has recently been added to the arsenal of characterization tools for material scientists to observe nanoscale surface features on both conducting and insulating materials. It is now therefore crucial to understand whether the intense electron beam will damage the features of interest. We have been able, for the first time, to measure and quantify this damage using a combination of HRSEM and atomic force microscopy (AFM), and as a consequence, we demonstrate that the bulk of the damage, expressed as a depression on the crystal surface, is confined primarily to a subsurface volume. Simulations demonstrate that the depth of the depression is proportional to the interaction volume of impact electrons below the crystal surface. More importantly, the nanometer surface features are conserved, and there is negligible associated loss of the critical information in nanoscopic surface topography. These results confirm the usefulness of HRSEM as a tool for surface analysis not only for scientists investigating crystal growth but also for materials scientists analyzing any surface at the nanoscale.