In Situ, Real-Time Monitoring of the Reductive Desorption Process of Self-Assmbled Monolayers of Hexanethiol on Au(111) Surfaces in Acidic and Alkaline Aqueous Solutions by Scanning Tunneling Microscopy

摘要

Reductive desorption processes of a self-assembled monolayer (SAM) of hexanethiol on an Au(111) surface both in H_2SO_4 and KOH aqueous solutions were investigated by in situ scanning tunneling microscopy (STM) in real time. The structure of the SAM int eh electrolvte solutions before the desorption ws confirmed to be same as that in the air, that is, the (1/2Z1/2)R30deg struture. The eesorption of th thiolate (thiol) molecules was found to e initiate from the defects in the SAM, that is, missing rows and the edge of the vacancy islands. Although the desorbed thiolate (thiol) moleculs formed aggregates both in H_2SO_4 and KOH solutins, the numbr and the size of the aggregates monitored by STM wer higher in H_2SO_4 solution than in KOH olution, reflecting the lower solubility and diffusion rate of the desorbed molecules in H_2SO_4 solution than in KOH solutin. The reconstructued, that is, 1/2X23), structure of Au(111) was observed after the desorpiton of the SAM in KOH solution, showeing that the clean surfce was exposed, although the vancany islands of monatomic height, which were observed on the SAm-covered gold, remained to be observed on the surface even after the desorption.