Delivered by Ingenta to: University of Waterloo IP : 129.97.47.66 Fri, 16 Apr 2010 14:28:58 Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 10, 3988–3993, 2010 Influence of Mo on the Growth of Single-Walled Carbon Nanotubes in Arc Discharge Huafeng Wang 1∗ , Zhenhua Li 2 , Sakae Inoue 1 , and Yoshinori Ando 1 1 21st COE Program “Nano Factory,” Department of Materials Science and Engineering, Meijo University, Nagoya 468-8502, Japan 2 Department of Mechanics, Zhejiang University, Hangzhou 310027, China In this study, we investigated the role of Mo on the growth of single-walled carbon nanotubes (SWNTs) in arc discharge method. Mo with various concentrations was incorporated into two typical arc systems, namely Ni/Y-He and Fe-Ar/H 2 . Based on analyses of yield and purity, we found the best concentration of Mo is 0.5 at% in Ni/Y-He system and 0.3 at% in Fe-Ar/H 2 system. For both systems, the incorporation of Mo has dramatically increased the yield of soot in their best concentrations. On the contrary, the promotion effects of Mo on purity of SWNTs were not same. Thermal gravimetric analysis showed that with the addition of Mo, the purity of SWNTs did not change effectively for Ni-Y/Mo-He system, but noticeable increment of purity was observed for Fe/Mo-Ar/H 2 system from 33 wt% to 50 wt%. Considering on these experimental results, we prove that Mo plays a positive role in arc discharge for the enhancement of SWNTs growth. Keywords: Single-Walled Carbon Nanotubes, Arc Discharge, Synthesis, Mo. 1. INTRODUCTION The method of arc discharge is widely used to produce single-walled carbon nanotubes (SWNTs) for its high- efficiency and good product quality. It may be the easiest way to get SWNTs compared to chemical vapor deposi- tion (CVD), laser ablation and any other methods. 1 In the past decades, researchers around world have done exten- sive works in order to improve the purity and quality as well as to control SWNTs structure such as chirality, diam- eter and so on by varying its growth conditions. 1–5 Till now, it is commonly recognized that using Ni/Y catalyst in helium, 1 Fe in mixture gas of argon and hydrogen 2 are very efficient way to get SWNTs by arc discharge. How- ever, the purity of as-grown products by this method is still far from satisfied, it is worth conducting researches to improve it. In view of synthesis of SWNTs, the selection of metal catalyst is the key for any methods. Although the growth mechanisms of SWNTs are still not clear, same kind of metals such as Fe, Co and Ni or their combinations have been used as catalysts in the arc discharge and CVD method. 36–8 It has been reported that the yield of products increases or the catalyst becomes more selective in grow- ing SWNTs when Mo is incorporated in CVD system. 69 Since Mo plays a positive role and works as an effective ∗ Author to whom correspondence should be addressed. promoter in CVD process, it is reasonable to try it in arc discharge because almost no research has been done in producing SWNTs with the help of Mo by this method. This paper focuses on the influence of Mo on the growth of SWNTs in arc discharge. We have selected two typ- ical arc discharge systems (Ni/Y-He 1 and Fe-Ar/H 2 2 ) to perform experiments. Mo with various concentrations is incorporated in these two systems. The yield, purity, ease of purification and diameter distribution of as-grown samples are characterized and used to evaluate the effects of Mo. Based on our experimental results, the optimal concentrations of Mo for these two systems have been obtained. We also propose some explanations on the role of Mo in arc discharge according to the theory of growth mechanisms. 2. EXPERIMENTAL DETAILS The cathode and anode were vertically fixed at the center of water-cooled chamber. The upper side movable cathode (diameter 10 mm, pure graphite rod) was used to adjust distance between two electrodes during arc evaporation. The down side anode was graphite rod with metal cat- alysts (square shape, 6.5 mm × 6.5 mm). In this paper, we have used Mo in two systems, namely Fe-Ar/H 2 and Ni-Y/He system. Same technique was applied to prepare the anode in two systems. The anode with homogenously 3988 J. Nanosci. Nanotechnol. 2010, Vol. 10, No. 6 1533-4880/2010/10/3988/006 doi:10.1166/jnn.2010.1971