SECONDARY-ELECTRON IMAGING OF DISORDERED SUBMONOLAYERS

Secondary-electron imaging (SEI), which allows real-time imaging of near-surface structures in real space, is applied to a (111) surface of an Al-3at%Ag alloy. In the fully segregated state, the Ag surface concentration is 0.3 monolayers. Although there is no long-range order, as evidenced by the absence of a low-energy electron-diffraction pattern, an analysis of the SEI image shows that a significant fraction of Ag atoms occupy three-fold symmetric hollow sites in stacking-fault positions. SEI is shown to be a useful new technique for structural studies of evolving surfaces even with submonolayer coverages, such as growing films with short-range order.