Scanning Tunneling Microscopy Examination of Rubrene Deposited on Au(111) in Aqueous Solution

Abstract

Rubrene has received much attention for its potential in the fabrication of organic thin film transistors (OTFTs), and the interface between rubrene and metal leads, such as those made of gold, is important in this context. In this study in situ scanning tunneling microscopy (STM) was used to examine rubrene molecules deposited on a Au(111) electrode from a 8 or 80 μM benzene dosing solution under potential control in 0.1 M perchloric acid. Immersion in either dosing solution for 10 min or longer yielded ordered structures featuring parallel stripes aligned in the ⟨121⟩ direction of the Au(111)-(1×1) surface. Unusual surface features of ragged step edges and one-atom-deep pits were observed on the heavily dosed Au(111) sample, which suggests unexpected rubrene-induced restructuring of the gold substrate. Roughly 0.1 monolayer gold adatoms were codeposited with rubrene molecules on the Au(111) electrode. Molecular-resolution STM imaging suggests an upright adsorption configuration of rubrene molecules anchored with two phenyl groups on the Au(111) electrode. Ordered rubrene adlattices were seen between 0.1 and 1.0 V (vs reversible hydrogen electrode), but disappeared at E < 0 V, leading to aggregates of gold atoms. These results lend support to the proposed restructuring of the gold surface.