CV and in situ STM study the adsorption behavior of benzoic acid at the electrified Au(100)| HClO4 interface: Structure and dynamics

• Four highly long-range ordered adlayers of BA on the Au(100) and the potential induced phase transition were revealed by in situ STM
• The hydrogen bond, van der Waals and molecule–substrate interaction determines the pattern and orientation of the adlayers
• Phase transitions between the various types of adlayers occurs according to a nucleation and growth mechanism

In situ STM and electrochemical methods have been used to study the adlayer structures of benzoic acid (BA) at electrified interfaces between Au(100) single crystal in contact with 0.1 M HClO4 solution. Depending on the electrode potential, BA formed four highly long-range ordered adlayers on Au(100) substrate. The structure of adlayers was imaged with molecular resolution. At the negative charge, planar-oriented BA molecules formed dimers decorated on electrode surfaces referred as linear dimer structure, tilted stripe phase, and chicken-wire pattern, which were stabilized via hydrogen bonding and by weak substrate-absorbate interaction. Increasing the electrode potential to positive charge densities causes to the desorption of the physisorbed hydrogen-bonded network and the formation of an ordered chemisorbed adlayers accompanied by the reorientation of BA molecules from planar to a tilted orientation in the chemisorbed region, which denoted as double stacking row phase. Furthermore, potential-induced formation and dissolution of BA monolayers were investigated. Structural transitions between the various types of ordered adlayers occurs according to a nucleation and growth mechanism.