Beam-Induced Motion of Adatoms in the Transmission Electron Microscope

Equations governing the elastic scattering of electrons are applied to the knock-on displacement of atoms along a substrate, yielding analytical expressions for the surface-translation energy, threshold incident energy, and displacement rate. For a surface perpendicular to the incident beam, scattering angles around 90 degrees contribute most to the kinetic energy of surface atoms. Tilting the specimen lowers the threshold incident energy for displacement and leads to anisotropy in the atomic motion but has little effect on the directionally-averaged displacement rate. The rate of beam-induced adatom motion is predicted to exceed that of room-temperature thermal motion when the surface-diffusion energy is greater than about 0.5 eV.