We report the studies of redox-active ferrocene (Fc) and tetrathiafulvalene (TTF) derivative islands embedded in n-decanethiol self-assembled monolayers on Au(111) using electrochemical scanning tunneling microscopy (EC-STM). We performed EC-STM measurements of both islands of varied sizes at various potentials in 0.05 M HClO4 solution. While the apparent height of Fc islands depended on the tip and sample potentials, that of TTF islands did not depend on the potentials except in the case of very small islands (less than ten molecules). Furthermore, the larger the size of TTF islands, the higher the apparent height in the STM images. This is quite contrary to the case of Fc islands where the apparent height did not depend on the island size. We rationalize these behaviors in terms of the differences in intermolecular interaction and effective electron transfer between redox-active moieties.
