Electronic structure of Si(001)-c(4x2) analyzed by scanning tunneling spectroscopy and ab initio simulations

We used atomic scale scanning tunneling spectroscopy to map the surface local density of states (LDOS) of clean Si(001)-c(4x2) at 80 K. Energetically and spatially resolved LDOS images show that the intensity of the controversial 1.4 eV feature in the empty states is high over the troughs between dimer rows and low over the dimers. In contrast, the intensities are inverted in images constructed at 2.1 eV. To understand those results, we undertook ab initio calculations using a real-space implementation of density functional theory to obtain contour plots of the surface charge density and the distribution of eigenstates. The simulations demonstrate that the features at 1.4 and 2.1 eV arise from the π* and σ* states, respectively, and that π bond interaction between dangling bonds persists in the buckled dimer configuration.