Impact of Surface Dipole on Resonant Electron Injection in Scanning Tunneling Spectroscopy

Resonant electron injection and first-principles calculations are utilized to study single-adsorbed selenium (Se) atom on a Si(111)-7×7 surface. Theoretical calculations indicate that a negative dipole of 0.61 eV forms toward the adsorbed Se atom due to electron trans-fer from the associated Si atoms. The formation of surface dipole modifies the effective tunneling barrier height and causes a shift in the energy of the resonant state formed in the vacuum gap between the tip and the sample surface. The experimental data imply that an outward negative surface dipole of 0.61 eV causes a resonant electron injection bias shift to high voltage of about 0.45 V.