A theoretical analysis of the scanning tunnelling microscopy image of the Sn/Ge(111)-(3 x 3) surface was presented. In a first step, the atomic structure was reached using a combination of local-orbital and plane-wave density functional methods. A ground state geometry presenting two different types of Sn adatom was found, with vertical positions differing by ≈0.3Å. In a second step, this geometry was used to analyze the tunnelling currents of this surface in a typical scanning tunnelling microscopy experiment. In the present approach, a Keldysh formalism was used with a coupling between tip and the sample defined by Bardeen-matrix elements: the tunnelling currents were found to depend on the semiconductor surface density of states and these Bardeen coupling elements. A scanning tunnelling microscopic study was made of the surface corrugation for positive and negative biases, and it was found that the scanning tunnelling microscopic images were complementary to each other; in good agreement with the experimental evidence.

Surface Geometry and STM Image of the Sn/Ge(111)-3 x 3 Reconstruction. L.Jurczyszyn, J.Ortega, R.Pérez, F.Flores: Surface Science, 2001, 482-485[2], 1350-4