Electronic effects at self-assembled 4,4′-thio-bis-benzenethiolate protected Au nanoparticles on p-GaAs (1 0 0) electrodes

Abstract

The effects of the self-assembled 4,4 -thio-bis-benzenethiolate protected gold nanoclusters onto a p-GaAs (1 0 0) electrode were examined by AFM, XPS, SHG and EIS investigations. The AFM and XPS results revealed a well-ordered overlayer exhibiting a bi-modal highly correlated fractal behavior which, however cannot fully protect the semiconducting surface against the oxidation in air. The EIS data pointed out the influence exerted by the gold-monolayer protected clusters (Au-MPCs) over the charging/dischargingprocesses observed at p-GaAs (1 0 0) electrode. Although the applied potential is varied linearly, the potential drop within the semiconductor space charge region as well as that across the Au-MPCs layer undergoes stepped changes supposed to result in the discrete charging of the Au-MPCs. These effects point to an electronic equilibrium between the Au-MPCs and the semiconducting substrate. Fermi level pinning and enhancement of the SHG response in the potential range where the surface/interface states in the semiconductor band gap become electrically active bring further proof in this respect.