Fabrication of carbon microelectrodes with an eective radius of 1 nm Shengli Chen, Anthony Kucernak * Department of Chemistry, Imperial College of Science Technology and Medicine, London, UK SW7 2AZ Received 6 November 2001; received in revised form 13 November 2001; accepted 14 November 2001 Abstract A method for producing insulated nanometer-sized carbon electrodes is presented. These electrodes are produced using elect- rochemical etching of carbon ®bers followed by deposition of electrophoretic paint. A new deposition approach for insulating the tips, the so-called ``inverted deposition'' technique, is introduced. This technique allows complete insulation of the whole body of the etched carbon ®ber except for the very tip, leaving an electrochemical active area with eective diameters as small as a few na- nometers. The process overcomes pinhole formation that can be a problem with the normal electrophoretic paint deposition process. The fabricated electrodes show ideal steady-state voltammetric behavior. The voltammetric response corresponding to the reduction of hexacyanoferrateIII) and hexaamminerutheniumIII) is investigated on these small electrodes in the absence and presence of supporting electrolyte. For these two multiple-charged ions the steady-state voltammetric behavior in the absence of supporting electrolyte is found to deviate from expected behavior, especially at very small electrodes. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Nanometer-sized electrode; Carbon ®ber; EDP insulation; Absence of supporting electrolyte 1. Introduction During the last two decades there has been wide- spread and growing interest in fabricating and charac- terizing electrodes with nanometer dimensions due to the novel applications of such ultrasmall devices and the unique electrochemistry at the interface between indi- vidual nanoelectrodes and the electrolyte [1±4]. Prepa- ration of ultrasmall electrodes involves two crucial steps. First, a commercially obtained microwire of the elec- trode material has to be signi®cantly thinned down to form a tapered tip with the end of nanometer dimen- sions. This thinning task is generally accomplished by various etching techniques [1,5±9]. The other crucially important step is insulation of the whole of the surface of the etched wire except the very apex of the tip, thus exposing only a very tiny electrochemically active area to the electrolyte. Several research groups have reported within the literature the fabrication of individual Pt electrodes having electrochemically active radii as small as several tens of nanometers, and even down to a few nanometers [1,2,5,6]. The achievement of exposing a tip with electroactive radii of only a few nanometers relies on ecient insulation methods. Several methods have been previously used, for instance, translating the etched tips through a molten glass bead at controlled speed [1] or the use of a laser micropipette puller [2]. Compared to these approaches the method employing electrophoretic deposition of a polymer paint EDP) [5,6,10] seems to be particularly straightforward and practical since no complicated experimental setup is required. Although carbon microband electrodes have been produced with one dimension less than 50 nm [11], and uninsulated carbon ®ber electrodes 10±100 lm long and with tip diameters of ca. 100 nm have been produced [12], no one has reported fabrication of carbon elec- trodes having electroactive surfaces of equivalent radii less than about 100 nm. Moreover, as carbon is a ver- satile electrode material that can undergo various chemical and electrochemical modi®cations it is possible Electrochemistry Communications 4 2002) 80±85 www.elsevier.com/locate/elecom * Corresponding author. Tel.: +44-20-74945831; fax: +44-20- 75945804. E-mail address: [email protected] A. Kucernak). 1388-2481/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1388-248101)00278-8
