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

We present tunneling spectra for nanometer scale Au dots on in situ. oxidiz ed Si(100). The spectra were measured for dots fabricated on clean and oxid ized surfaces for oxide thickness from 0 to 1 ML. Two important features ar e observed. First, tunneling current-voltage spectra of the dots on the ato mically clean surfaces show metallic behavior, confirming the identificatio n 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 associ ate this feature with oxide related defect sites which we observe at densit ies that increase from 0.06 to 0.3/nm(2) as oxide coverage increases from 0 .1 to 1 ML. The probability of observing this feature through a gold dot in creases by about a factor of 2, suggesting that the dot increases the effec tive sampling area of the defect sites by the same factor. (C) 2001 America n Vacuum Society.