Tunneling barrier height at defect sites on Si(001)

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Tunneling barrier height (BH) has been measured at two types of surface defects on Si(001), the type-C defect and the split-off-dimer defect. Contrary to previous experiments, we find no evidence of large BH reduction at these defect sites. For both defects, the measured BH contour shows a good agreement with the STM topographic contour. The spatial variation in BH is thus dominated by the topographic contribution at these dimer defects, as well as at normal dimers. Our experimental results suggest that a large defect-induced dipole is quite unlikely at type-C and split-off-dimer defects.