Instability of metallic In-Sn dimer lines on Si(100) 2×1 surface

The stability of mixed In-Sn dimer chains on Si(100) 2×1 surface is studied from first-principles calculations. These one-dimensional systems could be metallic since each dimer carries an odd number of electrons. Ab initio results are discussed in the light of a simple orbital model that relates the occupancy of the dangling bond to the local geometry. The mixed dimers are stabilized in a structure based on a sequence of two asymmetric adjacent In-Sn Sn-In dimers. This Jahn-Teller-type distortion involves charge transfer between atoms more than 0.4 nm apart. The corresponding system is predicted to be insulating as expected from classical models of one-dimensional metals. The calculated geometry is consistent with ultrahigh vacuum scanning tunneling microscopy (STM) images. It highlights the difficulty of STM image interpretation due to the lack of chemical selectivity.