Atomic dipole moment distribution on a hydrogen-adsorbed Si(111)-(7 × 7) surface observed by noncontact scanning nonlinear dielectric microscopy

Noncontact scanning nonlinear dielectric microscopy (NC-SNDM) can atomically resolve the polarization distribution on material surfaces. We observed a hydrogen-adsorbed Si(111)-(7 × 7) surface using NC-SNDM and found that hydrogen-adsorbed Si adatoms had lower dipole moments than bare Si adatoms. We discuss the charge distribution around a hydrogen-adsorbed Si adatom in terms of its geometry and the electronegativities of hydrogen and silicon. Our model suggests that the charge distribution around a hydrogen-adsorbed adatom is nearly symmetric and it qualitatively explains the experimental results. We thus conclude that the hydrogen-adsorbed Si adatoms are both electrically and chemically passivated.