Scattering potentials at Si-Ge and Sn-Ge impurity dimers on Ge(001) studied by scanning tunneling microscopy and ab initio calculations

Scattering potentials for π electrons at Si-Ge and Sn-Ge dimers on a Ge(001) surface are studied by scanning tunneling microscopy and ab initio calculations. Phase-shift analysis of standing waves in dI/dV images reveals that Si and Sn atoms located in the conduction path of π electrons form potentials with the sign opposite to each other. Density-functional calculations and simple calculations based on the nearly-free-electron model explain the observed potential structures. These results are qualitatively understood by relative p -orbital energy of the Si, Sn, and Ge atoms.