Initial Oxidation Structure of Chlorinated Si(001)

The Cl-saturated Si(001) surface is investigated by employing density functional theory calculations. From the electronic density of states, the low-and the high-bias filled-state images and the empty-state images are found to originate from Cl(3p) states directed in-plane, in parallel with the Si dimer row, and perpendicular to the surface (z), respectively. The bright triplet, which is a characteristic scanning tunneling microscopy (STM) feature of an unchlorinated bare Si dimer, is attributed to an occupied dangling bond state of the bare Si dimer that is hybridized with the neighboring Cl(3p(z)) orbital. The previously observed split-dimer feature is confirmed to be the dimer-bond oxidized structure. Finally, we suggest that the initial back-bond oxidation does not occur on the chlorinated Si(001) surface because it is energetically not favored compared with dimer-bond oxidation and because its STM simulation does not match experimental images.