Chemical identification in the (1 0 0) surface using scanning tunneling microscopy and first-principles calculations

We describe the geometric, energetic and electronic structure of the Cu 3 Au (1 0 0) surface using a combination of scanning tunneling microscopy (STM) and first-principles calculations based on density-functional theory (DFT). Our calculations show that the half–half Cu–Au termination is the one with lower surface energy, in agreement with experiments. The surface atomic rippling proposed by experimental data is also well reproduced by the calculations. STM images with atomic resolution display interesting voltage dependence, showing both types of atoms in the surface unit cell for lower voltages but just one type for higher voltages. Comparisons with theoretically simulated STM images and cross-sectional density of states profiles allows for an unambiguous assignment of Au atoms as the one appearing in higher-voltage images, thus providing chemical identification at the surface.