Growth Processes and Reductive Desorption Behaviors of 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111)

Abstract

Growth processes and electrochemical behaviors of 4-fluorobenzenethiol (4-FBT) self-assembled monolayers (SAMs) on Au(111) prepared by vapor deposition at 323 K were examined using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging revealed that 4-FBT SAMs at the initial growth stage (deposition for 1 min) were mainly composed of bright molecular aggregates and liquid-like disordered phase. After longer deposition for 3 min, 4-FBT SAMs had three distinct surface features: a few molecular aggregates, small ordered domains, and disordered phase. These small ordered domains with sizes ranging from 5 to 10 nm had a (4 x root 3)R30 degrees packing structure. As deposition time increased to 24 h, long-range ordered domains larger than 40 nm were formed on Au(111) surfaces. From this STM study, we demonstrate that phase transitions of 4-FBT SAMs on Au(111) occur from molecular aggregates to large ordered domains via formation of small ordered domains as deposition time increases. CV measurements showed reductive desorption peaks for 4-FBT SAMs in the range of -638 similar to -648 mV regardless of SAM morphology, suggesting that S-Au binding strength of 4-FBT SAMs on Au electrodes is a dominant factor for electrochemical stability.