A rotating gold ring  /gold disk electrode study on electrochemical reductive desorption and oxidative readsorption of a self-assembled monolayer of dodecanethiol Toshihiro Kondo, Takayoshi Sumi, Kohei Uosaki  Physical Chemistry Laboratory, Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Received 16 January 2002; received in revised form 20 May 2002; accepted 4 June 2002 Abstract The electrochemical reductive desorption and oxidative readsorption of a self-assembled monolayer (SAM) of dodecanethiol (C 12 SH) in an alkaline solution were investigated using a rotating gold ring  /gold disk electrode. Dodecanethiolate (C 12 S  ), which was reductively desorbed from the C 12 SH SAM modified gold disk electrode, was detected by the gold ring electrode which was kept at a potential where the oxidative readsorption took place. As the rotation rate was increased, the cathodic peak potential for the reduction of the SAM at the disk electrode became more positive and the full width at half maximum of the anodic peak for the oxidative readsorption at the ring electrode decreased. These results suggest that reductively produced C 12 S  tends to remain on the electrode surface and might form a molecular assembly such as a micelle on the disk electrode surface, thus preventing the residual C 12 SH SAM from desorbing. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Self-assembled monolayer (SAM) on gold; Alkanethiols; Reductive desorption; Oxidative readsorption; Rotating ring  /disk electrode (RRDE) 1. Introduction Self-assembled monolayers (SAMs) of alkanethiols on gold attract many research groups because of their great number of potential applications such as molecular devices [1,2]. We have reported that the various physi- cochemical properties of the SAMs are strongly depen- dent on the structural order of the SAMs [3] as well as on the morphology of the substrate [4]. Since Widrig et al. reported that alkanethiolates (RS  ) were electrochemically desorbed from a gold surface by the following one electron reduction process in an alkaline ethanol solution [5], AuSR e  0 Au RS  (1) many electrochemical studies of this reaction (I) have been carried out [6  /26] because the position and shape of the cathodic peak for the reductive desorption provide much information on the nature of the SAMs such as stability, adsorption energy, and orientation. For example, the longer the alkyl chain, the more negative is the peak potential for the reductive deso- rption, reflecting the stronger hydrophobic intermole- cular interaction of the alkyl chains. When the electrode potential is scanned back in the positive direction after the reductive desorption of RS  , the anodic peak due to the oxidative readsorption of desorbed RS  is observed as [5]; RS  Au 0 AuSR e  (2) The charge of this anodic peak is smaller than that of the cathodic peak for the reductive desorption [10]. One reason for the smaller anodic charge is that some of the desorbed RS  diffuses away from the electrode surface. The other reason is the formation of aggregates. Hobara et al. used an in situ scanning tunneling microscope (STM) to monitor the reductive desorption of propa- nethiol and hexadecanethiol SAMs from Au(111) and  Corresponding author. Tel.:  /81-11-706-3812; fax:  /81-11-706- 3440 E-mail address: uosaki@pcl.sci.hokudai.ac.jp (K. Uosaki). Journal of Electroanalytical Chemistry 538 /539 (2002) 59 /63 www.elsevier.com/locate/jelechem 0022-0728/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0728(02)01000-8