Room-temperature synthesis of single-wall carbon nanotubes by an electrochemical process Ahmed Shawky, Satoshi Yasuda, Kei Murakoshi * Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Hokkaido, Japan ARTICLE INFO Article history: Received 23 February 2012 Accepted 27 April 2012 Available online 11 May 2012 ABSTRACT Single-wall carbon nanotubes (SWCNTs) were produced by an electrochemical route by applying a small negative potential to a solution of acetic acid over a Au surface supporting Ni nanocatalysts. Ni nanocatalysts were grown electrochemically on Au surface and their particle sizes were controlled by deposition time. Raman spectroscopy and scanning probe microscopy observations of the catalyst and as-deposited samples and revealed that the catalyst structure strongly affects the SWCNT diameter distribution. The deposited carbon structure depended on the catalyst particle size and structure. Raman spectra confirmed the existence of selectively grown semiconducting SWCNTs with very narrow diameter distribution. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Single-walled carbon nanotubes (SWCNTs) have attracted a lot of interest since the landmark paper by Iijima and Ichih- ashi [1]. The unique properties of SWCNTs makes them suit- able for many applications including optoelectronic [2,3] and catalytic [4] applications as well as in nanodevices such as sensors [5], memory elements, and field-effect transistors [6–8]. Over the past decade and a half, the synthesis of SWCNTs has been greatly improved, resulting in orders of magnitude increases in nanotube lengths and yields [9,10]. Several research works have been performed seeking the selective growth of metallic or semiconducting SWCNTs with narrower chirality distribution in order to obtain unique prop- erties for direct use in applications [7,8,11–14]. However, there is still relatively feeble control of chirality and diameter distri- bution of such nanotubes which mainly determine its elec- tronic properties [15]. One reason why it is difficult to control SWCNTs is ascribed to the high temperature growth condition. Conventional techniques for synthesizing SWCNTs, such as arc discharge, laser ablation, and chemical vapor deposition (CVD), are performing high temperatures to activate the catalyst and decompose carbon feedstock. How- ever, such high temperature generates large thermal fluctua- tions at the nanocatalyst, which are expected to deform and aggregate particles. These dynamic changes to the catalyst during SWCNT growth are thought to induce particle aggrega- tion on the substrates by Ostwald ripening and altering the interaction between the catalyst and graphitic lattices, result- ing in the formation of SWCNTs with wide chirality distribu- tions [7,16,17]. This significant problem points out the extreme challenging to achieve diameter selectivity [18,19] or to develop a technique for production of uniform SWCNTs [13,16,20–22]. As to one of the solutions to develop selective SWCNT syn- thesis, an electrochemical approach would be considered. The thermal fluctuations should be reduced by this method because synthesis proceeds in the liquid phase and room temperature conditions. Consequently, it is expected to be a possible method for the selective growth of SWCNTs with well-specified structures. Carbon deposition was first per- formed by electrolysis using methanol and carbon dioxide as carbon sources [23,24]. A mixture of diamond-like carbon (DLC) and amorphous carbon has been produced from the 0008-6223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.04.068 * Corresponding author: Fax: +81 11 706 4810. E-mail address: kei@sci.hokudai.ac.jp (K. Murakoshi). CARBON 50 (2012) 4184 – 4191 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon