In-Situ Scanning Tunneling Microscopy Imaging of the Reductive Desorption Process of Alkanethiols on Au(111)

Abstract

The reductive desorption process of self-assembled monolayers of 1-hexadecanethiol, 1-propanethiol, and 3-mercaptopropionic acid on Au(111) has been studied in 0.5 M KOH solution by in-situ scanning tunneling microscopy (STM) and cyclic voltammetry. In-situ STM images of the monolayers at the potentials between −0.2 V and the reduction potentials of each thiols show the pits that are commonly seen in STM images of thiol self-assembled monolayers. A drastic morphological change takes place in the STM image around the peak potential in a cyclic voltammogram for the reductive desorption of adsorbed thiols. The images indicate that 3-mercaptopropionic acid molecules diffuse away from the surface after the reduction because of its higher solubility, while 1-propanethiol and 1-hexadecanethiol molecules stay in the vicinity of the surface forming aggregates. The partial recovery of the 1-hexadecanethiol monolayer after the anodic scan, suggested by cyclic voltammograms, is confirmed by STM, whereas 1-propanethiol aggregates remain at the surface without being reoxidized. The difference in the reoxidation behavior reflects the different amphiphilic properties of the desorbed molecules and the resultant molecular organizations formed on the surface.

Electrochemically controlled self-assembled monolayers characterized with molecular and sub-molecular resolution

“…Quantitative values of the coverage can be obtained by voltammetry [98][99][100][101][102][103][104] since electrochemical cleavage of the SAM S-Au bonds at negative potential follows reaction eqn (1). This one-electron reductive desorption process 105 should be accomplished in strongly basic solution (pH > 11) 100 to obtain precise coverage values and to avoid interference with dihydrogen evolution as well as to ascertain complete desorption.…”

Single Component Self‐Assembled Monolayers of Aromatic Azo‐Biphenyl: Influence of the Packing Tightness on the SAM Structure and Light‐Induced Molecular Movements

“…Both target compounds form SAMs by binding to the gold surface via their thiolate anchor-groups. Hence, by cycling the potential applied to the gold electrode their desorption (reductive, negative potential E c ) and possibly re-adsorption (oxidative, positive potential, E a ) behavior, which occurs according to reaction (II) [69][70][71] Au À S À R þ e À Ð Au þ À S À R…”

Electrochemical oxidative adsorption and reductive desorption of a self-assembled monolayer of decanethiol on the Au(111) surface in KOH+ethanol solution

“…Au -SR + e -=> Au + RS - (1) many electrochemical studies of the reaction (1) have been carried out because the peak area and the shape of the cathodic peak for the reductive desorption and its peak potential provide useful information of the SAM such as the adsorbed amount, stability, adsorption energy, orientation, and substrate morphology [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. For example, it was found that the longer the alkylchain, the more negative the reductive peak potential, reflecting the stronger van der Waals attractive interaction among alkylchains [17].…”

“…For example, it was found that the longer the alkylchain, the more negative the reductive peak potential, reflecting the stronger van der Waals attractive interaction among alkylchains [17]. The reductive desorption process has been investigated by many techniques including electrochemistry [17][18][19][20][21][22][23][24][25][26], FT-IR [27][28][29], electrochemical QCM [30][31][32], and in situ STM [33][34][35][36]. Several groups suggested the formation of an "aggregate" or "micelle" near or on the electrode surface after the reductive desorption of the SAM [28,33,35].…”