Effects of Fe film Thickness and Ammonia on the Growth Behavior of Carbon Nanotubes grown by thermal Chemical Vapor Depo
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Effects of Fe film thickness and ammonia on the growth behavior of carbon nanotubes grown by thermal chemical vapor deposition Jung Inn Sohn, Chel-Jong Choi, Tae-Yeon Seong and Seonghoon Lee Department of Materials Science and Engineering, Kwangju Institute of Science and Technology (K-JIST), Kwangju 500-712, Korea ABSTRACT The growth behaviour of carbon nanotubes on the Fe-deposited Si (001) substrates by thermal chemical vapor deposition (CVD) has been investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The Fe films are deposited for 20 s – 20 min by pulse-laser deposition. SEM results show that the growth characteristics of carbon nanotubes strongly depend on the Fe film deposition time. TEM and SEM results show that the pretreatment annealing at 800 ºC causes the continuous Fe films to be broken up into nanoparticles 8 – 50 nm across and discontinuous islands 100 nm – 1.1 µm in size. It is shown that the Fe nanoparticles are essentially required for the formation of aligned carbon nanotubes. SEM results show that the growth behaviors of carbon nanotubes are strongly dependent on the pretreatment atmospheres. In addition, for the Ar gas-pretreated sample, a carbonaceous layer is formed near the surface region. TEM results show direct evidence that a base growth mode is responsible for the growth of carbon nanotubes in the present work. Based on the microscopy results, the pretreatment condition dependence of the growth behaviors of carbon nanotubes is discussed. INTRODUCTION Carbon nanotubes have attracted significant attention because of their potential technological applications, such as gas reservoirs, battery electrodes, and field emission displays [1–3]. In particular, vertically aligned carbon nanotubes are required for field emission device applications. Several growth methods of laser vaporization, arc discharge and CVD have been used to synthesize carbon nanotubes [4-9]. Terrones et al.[8] fabricated vertically aligned carbon nanotubes on pulse-laser deposited Co films on silica substrates by means of thermal CVD. Li et al.[8] used a method based on CVD catalyzed by Fe nanoparticles embedded in mesoporous silica and produced large areas of vertically well-aligned long carbon nanotubes. Fan et al.[9] also synthesized aligned nanotubes on Fe-patterned porous Si substrates using thermal CVD. However, detailed studies of the effects of the structures of Fe films on the growth of nanotubes have not been hitherto performed. In this work, we investigate the effects of the Fe film thickness and pretreatment atmospheres on the growth behavior of carbon nanotubes. It is shown that the growth characteristics are significantly affected by the Fe film deposition time and pretreatment atmospheres. EXPERIMENTAL Carbon nanotubes were grown on Fe-deposited Si (001) substrates by thermal CVD. Fe films were deposited by pulse-laser deposition (PLD). Deposition time varied from 20 s to 20 min to control the thickness of the Fe films. (A Si substrat
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