Rümmeli et al. Nanoscale Research Letters 2011, 6:303 http://www.nanoscalereslett.com/content/6/1/303 N A N O R E V I E W Open Access Synthesis of carbon nanotubes with and without catalyst particles Mark Hermann Rümmeli1,2*, Alicja Bachmatiuk1, Felix Börrnert1, Franziska Schäffel3, Imad Ibrahim1,2, Krzysztof Cendrowski1,4, Grazyna Simha-Martynkova5, Daniela Plachá5, Ewa Borowiak-Palen4, Gianaurelio Cuniberti2,6 and Bernd Büchner1 Abstract The initial development of carbon nanotube synthesis revolved heavily around the use of 3d valence transition metals such as Fe, Ni, and Co. More recently, noble metals (e.g. Au) and poor metals (e.g. In, Pb) have been shown to also yield carbon nanotubes. In addition, various ceramics and semiconductors can serve as catalytic particles suitable for tube formation and in some cases hybrid metal/metal oxide systems are possible. All-carbon systems for carbon nanotube growth without any catalytic particles have also been demonstrated. These different growth systems are briefly examined in this article and serve to highlight the breadth of avenues available for carbon nanotube synthesis. Introduction The current excitement in carbon nanotubes (CNTs) was triggered by Sumio Iijima’s Nature publication in 1991 [1]. At that time there was a considerable interest in developing the arc evaporation method, initially dis- covered by Huffman and Krätschmer [2], for the pro- duction of C60 in macroscopic amounts. Iijima analysed the deposit on the cathode and found macroscopic amounts of multi-walled carbon nanotubes (MWNTs) and facetted graphitic particles. The lack of fullerenes in the sample was unexpected. Moreover, the excitement at that time in carbon nanostructures, born out of the discovery of fullerenes [3] was a further favourable fac- tor and so his publication drew significant attention. Iiji- ma’s next step was to see if he could fill these structures with transition metals. Transition metals were mixed into the graphitic electrodes and the arc evaporation process was run. The resultant product sprung another surprise. This time, a new form of carbon nanotube, namely, single-walled carbon nanotubes (SWNTs) with diameters between 1.1 and 1.3 nm were obtained [4]. Almost at the exact same time Donald S. Bethune, at IBM research laboratory, made the same discovery (see Figure 1) [5]. The discovery of SWNT was particularly * Correspondence: m.ruemmeli@ifw-dresden.de 1IFW Dresden, P.O. Box 270116, 01069 Dresden, Germany Full list of author information is available at the end of the article exciting due to interesting structure-property correla- tions. In addition, it highlighted the use of transition metals as catalysts for carbon nanotube synthesis. Over the next years, a massive amount of synthesis routes and variations were developed. Most of these were based on the use of catalyst particles, including the che- mical vapour deposition (CVD) route. CVD synthesis of CNT is facile and can be set up in laboratories without difficulty. Moreover, it is easily scaled up for mass pro- duction and so has developed into the most popular technique. Metal catalyst particles Vapor-grown CNT generally use metal catalyst particles and some even claim CNT synthesis requires a catalyst for their formation, despite Iijima’s original work on MWNT synthesis never having used a catalyst. The use of metal catalysts and filamentous carbon from vapour- based routes has a long history dating back well before Iijima’s landmark work, perhaps even as far back as 1889 [6]. For the most part 3d valence transition metals such as Fe, Co and Ni were used for the catalytic growth of CNT. More recently, several groups have grown CNTs from metals such as Au, Ag and Cu [7-10] and poor metals, e.g. Pb, In [11,12]. The conventional arguments for CNT growth are argued to occur in a similar manner to the model proposed for filamentous © 2011 Rümmeli et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.