Scanning tunneling spectroscopy of field-induced Au nanodots on ultrathin oxides on Si(100)

Abstract

We present tunneling spectra for nanometer scale Au dots on in situ oxidized Si(100). The spectra were measured for dots fabricated on clean and oxidized surfaces for oxide thickness from 0 to 1 ML. Two important features are observed. First, tunneling current–voltage spectra of the dots on the atomically clean surfaces show metallic behavior, confirming the identification of the dots as deposited Au from the tip. Second, tunneling spectra from Au dots on the partially oxidized surfaces show a feature at approximately 2 V (sample positive) with weak negative differential resistance. We associate this feature with oxide related defect sites which we observe at densities that increase from 0.06 to 0.3/nm2 as oxide coverage increases from 0.1 to 1 ML. The probability of observing this feature through a gold dot increases by about a factor of 2, suggesting that the dot increases the effective sampling area of the defect sites by the same factor.