Dimer exchange mechanism for substitutional As adsorption on Si(100)

We present first-principles calculations which support a dimer exchange mechanism for substitutional As adsorption on Si(100) surfaces. In contrast to the prevailing picture, we find that the origin of the substitution of the underlying Si atoms by As is the flexible reconstructions of the Si atoms in the resulting geometries, including the newly discovered π bonded reconstruction between the top-layer and the second-layer Si atoms. Calculated scanning tunneling microscopy images of the resulting As-Si heterodimer and the As dimer differ prominently from that of the Si dimer.