AVS 53rd International Symposium
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS2-TuM

Paper NS2-TuM13
Electrochemical STM Investigations of Redox-Active Tetrathiafulvalene Islands Embedded in Alkanethiol SAMs

Tuesday, November 14, 2006, 12:00 pm, Room 2020

Session: Nanoscale Manipulation and Assembly
Presenter: Y. Yokota, Tokyo Institute of Technology, Japan
Authors: Y. Yokota, Tokyo Institute of Technology, Japan
A. Miyazaki, Tokyo Institute of Technology, Japan
K. Fukui, Tokyo Institute of Technology, Japan
T. Enoki, Tokyo Institute of Technology, Japan
M. Hara, Tokyo Institute of Technology, Japan
Correspondent: Click to Email
Stochastic apparent height changes in scanning tunneling microscopy (STM) images of self-assembled monolayers (SAMs) have been reported by some groups.@footnote 1,2,3@ From the viewpoint of molecular electronics, one of the goals of our studies is to control the structure and electronic properties of molecular assemblies by using electric charging effects. We report the electrochemical STM (EC-STM) studies of redox-active tetrathiafulvalene (TTF) islands embedded in n-decanethiol (C10SH) SAMs on Au(111).@footnote 4@ We performed EC-STM measurements of TTF islands of varied sizes at various potentials in 0.05 M HClO@sub 4@ solution. While the larger island always protruded from the C10SH matrix independent of potential, the smaller island (less than ten molecules) changed their apparent height from flat surface to clear protrusion. This change was reversible against potential change. From the cyclic voltammetry of TTF SAMs, the electronic states of TTF moieties in each STM images were characterized. The behavior of the apparent height change of the smaller island can be explained by the orientational change induced by charging of TTF moieties. Meanwhile, the behavior of the potential-inactive one is associated with a stacking effect of TTF moieties in the large island. These results indicate that not only the oxidation state but also the orientation of the electroactive moiety responds to electrochemical potential and that orientational change is also a key factor in designing molecular devices under potential control. Furthermore, we report that the larger the size of the large islands, the higher the apparent height in the STM images, although the physical height of the islands can be assumed to be same. We think that the effective electron transfer between TTF moieties leads to increase of electron-transfer passes, and to the higher apparent height. @FootnoteText@ @footnote 1@ Z. J. Donhauser et al., Science 292, 2303 (2001). @footnote 2@ G. K. Ramachandran et al., Science 300, 1413 (2003).@footnote 3@ R. A. Wassel et al., Nano Lett. 3, 1617 (2003).@footnote 4@ Y. Yokota et al., J. Phys. Chem. B 109, 23779 (2005).