Nanometer-Scale Chemical Surface Analysis by Scanning (Tunnelling) Atom Probes

Abstract

An overview is given of the developments in the area of chemical surface analysis on the nanometer scale by ion mass spectrometry. Two main types of instrumentation are described. In one (the 'scanning atom probe', SAP), an extraction electrode with a small aperture (< 10 μm) is scanned at a short distance ( < 10 μm) from a rough surface. Field evaporation of atoms or small clusters from natural or artificial microtips at the surface and time-of-flight (ToF) analysis reveal the surface composition. In the other type (the 'scanning tunnelling atom probe', STAP), atoms or small clusters are transferred from a surface of a specimen to an STM tip. Subsequent field desorption from the tip and ToF analysis reveal the transferred particle's identity. First applications of constructed S(T)AP instruments show the capabilities and limitations of this new technique. Various designs and applications are described and factors that steer maturation and further developments are discussed. These factors are either intrinsic to the technique (e.g., surface diffusion, field evaporation, material transfer, etc.) or related to general developments in the science of small objects or thin films. The final goal is chemical analysis of single atoms or molecules from specific atomic surface sites.