Effect of C60 layer on the growth mode and conductance of Au and Ag films on Si(111)3-Au and Si(111)3-Ag surfaces

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The surface morphology and electrical conductance of C60-precoated Si(111)3-Au and Si(111)3-Ag surfaces have been monitored in the course of Au and Ag depositions. In both cases, the deposited metal atoms penetrate through the fullerene layers. However, the similarity in the growth mode does not result in similar dependencies of conductance versus deposited metal dose. Deposition of Au onto the C60-precoated Si(111)3-Au surface leads to a monotonic gradual increase in conductance starting from ∼0.4 ML Au coverage. Deposition of Ag onto the C60-precoated Si(111)3-Ag surface results in a nonmonotone peak-like dependence with a maximum at ∼0.5 ML of Ag. Both dependencies can be explained in terms of the acceptor-type behavior of the fullerenes, which trap the electrons donated by Au or Ag atoms. The difference between the two dependencies is a consequence of the difference in conduction mechanisms at the original surfaces, namely, the main conductance channel in Si(111)3-Au is the space-charge layer, while in Si(111)3-Ag it is the surface state band.