Diamond and Related Materials 12 (2003) 1851–1857 0925-9635/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0925-9635(03)00209-7 The role of nitrogen in carbon nanotube formation Chao Hsun Lin , Hui Lin Chang , Chih Ming Hsu , An Ya Lo , Cheng Tzu Kuo * a,b a a a a, Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, ROC a Photoetching Laboratory, Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu 310, Taiwan, ROC b Abstract To examine the role of nitrogen, Co- and Ni-coated substrates were pretreated with three different gas compositions to compare the pretreated catalyst surfaces; the Fe, Co and Ni foils were subjected to carbon nanotube (CNT) growth experiments with CH y 4 H and CH yN as source gases; the catalyst pretreatment plus the CNT growth experiments on Co- and Ni-coated Si substrates 2 4 2 were carried out using both microwave plasma chemical vapor deposition and electron cyclotron resonance chemical vapor deposition (ECR-CVD) under different nitrogen-containing gases. The results show that the role of nitrogen may be summarized as follows: by comparing with hydrogen plasma, the bombardment energy of nitrogen plasma is greater. Therefore, the presence of nitrogen during CNT growth can keep the front catalyst surface clean and active to prolong surface passivation to enhance carbon bulk diffusion. The higher temperature due to higher bombardment energy of nitrogen plasma can promote agglomeration effects during catalyst pretreatment and the initial stage of CNT growth to produce larger size nano-particles. The presence of nitrogen is a favorable condition for formation of the bamboo-like CNTs, but not a necessary condition. Another favorable condition for formation of the bamboo-like CNTs is to deposit CNTs by ECR-CVD.  2003 Elsevier Science B.V. All rights reserved. Keywords: Nitrogen; Formation mechanism; Bamboo-like nanotubes; Chemical vapor deposition 1. Introduction Since the discovery of carbon nanotube (CNT) by Iijima through the arc discharge method w1,2x, the nanostructured materials have become the hottest research topics in the world including their synthesis methods, growth mechanisms, property measurement, computational modeling, manipulation techniques and their potential applications w3x. The CNTs high Young’s modulus (f1.8 TPa) w4x, high aspect ratio structure, low density and unique electrical properties make them promising materials for use as tips of scanning tunneling microscope or atomic force microscope w5x. The excel- lent field emission properties also make them suitable as electron field emitters for field emission displays w6,7x. The assembly of CNTs into electronic circuits or as a field-effect transistor have pointed out an amazing future for nanotube electronic and spintronic device applications w8–13x. However, the mechanical and elec- *Corresponding author. Department of Materials Science and Engi- neering, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan, ROC. Tel.: q886-3-5731949; fax: q886-3- 5721065. E-mail address: ctkuo@cc.nctu.edu.tw (C.T. Kuo). trical properties of CNTs are highly depending on their chirality, diameter and structural defects w14x. The single-walled carbon nanotubes (SWNTs) have a more perfect graphite layer and can be synthesized by laser ablation or arc discharge methods w14x. However, the as-grown deposits from the above methods need post purification processes, and the lack of well devel- oped manipulation techniques so far retards the schedule of CNT commercialization. The chemical vapor depo- sition (CVD) methods, including microwave plasma enhanced CVD (MPCVD) w15–20x, thermal CVD w21– 25x, hot filament CVD and electron cyclotron resonance CVD (ECR-CVD) w27x, can directly be used to grow the aligned CNTs on a substrate. Moreover, the catalyst filmyparticle on the substrate can be patterned by many methods, such as lithography, transfer printing, evapo- ration or sputtering. The nanotubes can then be selec- tively grown on the catalyst-patterned substrates. The unique advantages of CVD methods, by comparing with other methods, are no need of post-treatments, i.e. purification and manipulation, and the ease of scaling up for mass production. But, its main disadvantage is the tendency to mainly form MWNTs with larger diam- eter and more defects, instead of SWNTs. The ‘hol-