Subnanometer imaging of adsorbate-induced electronic structure perturbation on silicon surfaces

Room-temperature scanning tunneling microscopy is utilized to explore the consequences of a single covalent bond formed between an organic molecule, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), and the Si(111)-7 × 7 surface at the atomic scale. Upon binding, both topographic imaging and spectroscopic techniques reveal significant charge rearrangement within the substrate that is delocalized from the organic adsorbate. With scanning tunneling spectroscopy, the spatial extent of this charge transfer is directly visualized and determined to extend up to 2 nm from the molecule predominately within half of the Si(111)-7 × 7 unit cell. Analysis of individual differential tunneling conductance spectra suggests that the charge transfer is mediated by the back-bonds of the silicon substrate.