AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP6
Heterogeneous Oxidation of the Si(111) Surface Determined by Kelvin Probe Force Microscopy

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: B Poelsema, University of Twente, The Netherlands
Authors: B Poelsema, University of Twente, The Netherlands
J.M. Sturm, University of Twente, The Netherlands
G.O. Croes, University of Twente, The Netherlands
H. Wormeester, University of Twente, The Netherlands
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A large change in work-function occurs during the initial oxidation of Si(111). The variation of the work-function after an initial exposure to O@sub 2@ allows the identification of a molecular precursor. An AFM with a conducting tip has been used as a Kelvin Probe Force Microscope (KPFM). It enables the in-situ, parallel recording of morphology and work-function with nanometer resolution. The clean Si(111) surface has been found to have a rms work-function variation of only 2 meV, indicative of an electrically very smooth surface. Exposure to molecular oxygen results in a very heterogeneous oxidation process in which morphology and work-function locally change in a non-correlated fashion. After an exposure of about 10 L(angmuir), the morphology remains similar, while over 100 L is required for the work-function to assume a stationary value. The change in work-function is only local as the average value is constant after 40 L and the rms of the work-function does not significantly change after 20 L. The heterogeneity of the oxidation process is also observed by a strong variation of the differential capacitance over the surface. This variation is strongly correlated to the local morphology indicating a large variation in local oxide thickness. The observations above can be rationalized via the presence of a molecular precursor. It actually has strong effects at sub-monolayer coverage.