Current-voltage characterisation of monolayer-supported Au-nanoclusters by scanning tunnelling microscopy under ambient conditions

摘要

The current-voltage characteristics of a double-tunnel junction based on a gold crystallite with a diameter of ca. 2 nm, separated from a gold surface by ca. 1 nm was investigated by scanning tunnelling microscopy. The sample architecture was built by attaching gold nanoparticles covered with 2-mercaptosuccinic acid to an atomically flat gold surface which was covered by a self-assembled monolayer (SAM) of 6-amino-1-hexanethiol. Surface plasmon and infrared spectroscopy as well as STM imaging were employed to identify suitable preparation conditions and prove the existence of the desired architecture. No reproducible steps in the current-voltage characteristics are observed on this system under ambient conditions. Nonetheless, a sound signature for tunnelling through the double-tunnel junction is established by a quantitative fit of the averaged experimental data to a theoretical model of a single-tunnel junction. Firstly, the current on the particle is strongly reduced at low absolute external voltage and secondly the current voltage characteristics are asymmetric. Since both deviations from theory are absent in reference experiments on the bare monolayer, they may serve as a robust signature for double-tunnel junctions and open the door to the investigation of single-electron tunnelling under ambient conditions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).