Potential-controlled structural evolution of Bromobenzene on Au(111): Insights from in situ STM

Abstract

The adsorption behavior of bromobenzene (BrB) on an Au(111) electrode was investigated using in situ scanning tunneling microscopy (STM) under potential control in 0.1 M sulfuric and perchloric acid solutions. Real-time STM imaging revealed that BrB adsorption induced immediate structural changes on the Au(111) surface, including the formation of 2.3 Å deep vacancy islands (VIs) and predominantly disordered BrB structures. The preferential interaction of BrB with Au adatoms, rather than the Au(111) terrace, likely drove VI formation. As the potential increased, BrB coverage expanded, leading to a structural transition from 1D molecular chains to 2D arrays, and eventually to a well-ordered 3D multilayer film. Concurrently, the BrB molecular orientation shifted from a flat-lying to an upright configuration. At positive potentials, the multilayer BrB film remained structurally stable but dissolved upon a negative potential shift and irreversibly decomposed at more negative potentials. Additionally, BrB assembled differently in perchloric acid, highlighting the critical role of anions in interfacial organization. Local linear BrB structures preferentially aligned along the 〈121〉 direction of Au(111), forming triangular fractal patterns and an increasingly disordered 3D film at positive potentials.