Electronic properties of self-assembled monolayers on Au(111) studied by electrical force spectroscopy - art. no. 205403

Localized voltage dependent capacitive currents through different self-asse mbled monolayers on Au(111) surfaces were studied by a spectroscopic method in a modified atomic force microscope that detects surface potentials and partial derivativeC/partial derivative (z) data as functions of an applied modulated and biased voltage between tip and sample. On flame-annealed Au s urfaces, the partial derivativeC/partial derivativez signal is completely v oltage independent. The signal amplitudes on 2-amino-alkanethiol layers cha nge with both ac and de voltage. The partial derivativeC/partial derivative z(U-dc) data obtained represent the energy-dependent density of states of t he investigated surface layer. Moreover, the charges of ligand stabilized c lusters and the dependence of the clusters' electrical properties on their size were reproduced. The results are discussed in connection with schemati c energy models and replacement circuits.