Formation and Structural Changes of 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111)

Abstract

The surface structure and electrochemical behavior of 4-fluorobenzenethiol (4-FBT) self-assembled monolayers (SAMs) on Au(111) formed by vapor deposition at 323 K as a function of deposition time were examined by scanning tunneling microscopy (STM) and cyclic voltammetry (CV) measurements. STM observations clearly revealed that 4-FBT SAMs after 10 min or 6 h deposition were composed of disordered and ordered domains containing many gold adatom islands. The size of ordered domains with a molecular row structure was also relatively small, ranging from 10 to 50 nm. After longer deposition for 24 h, the structural quality of 4-FBT SAMs was greatly enhanced with large ordered domains (>50 nm) and without gold adatom islands. CV measurements demonstrated that the blocking efficiency of the electrodes for redox reactions increased with the improvement in the structural quality of 4-FBT SAMs on Au(111), consistent with the STM results. Our results obtained here will be very useful in understanding the formation of 4-FBT SAMs on Au(111) and obtaining the high-quality SAMs.