Low Temperature Synthesis of Carbon Nanotube on Si substrate Using Alcohol Gas Source in High Vacuum
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1057-II14-03
Low Temperature Synthesis of Carbon Nanotube on Si substrate Using Alcohol Gas Source in High Vacuum Takahiro Maruyama, Kenji Tanioku, and Shigeya Naritsuka Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya, 468-8502, Japan ABSTRACT Carbon nanotube (CNT) growth in a high vacuum was achieved using alcohol gas source technique. Using Co catalyst, CNTs were grown on SiO2/Si substrate below 10-1 Pa without any carbon decomposition processes. By adjusting the growth pressure and temperature, we successfully grew CNTs under 1×10-4 Pa. In addition, we achieved CNT growth at 400oC by reduction of the growth pressure. We also investigated the relation between the growth condition and CNT diameter by Raman spectroscopy and showed that average diameter decreased as the growth pressure was reduced. INTRODUCTION Carbon nanotubes (CNTs) have been expected for a lot of applications as electronic devices due to their excellent electronic properties, for example, a field effect transistor (FET)[1, 2], an electron emitter [3] and wiring for LSI [4, 5]. Although the electronic properties of CNTs are strongly dependent on the structures, growth mechanism of CNT has not been evident, and control of CNT structure has never been realized. For clarification of growth mechanism, in situ observation of CNT growth is effective and CNT growth in a high vacuum is essential to perform in situ observation during CNT growth. In addition, the effects of residual gases also may be avoided in the growth under high vacuum. To date, CNT growth under low pressure has been reported by several groups. Homma et al. reported CNT growth under 20-40 Pa using ACCVD [6]. Recently, Shiokawa et al. grew SWNT by catalytic CVD at 0.05 Pa in an ultra-high vacuum (UHV) chamber [7]. However, in their growth conditions, the local pressure at the substrate was similar to that measured at the vacuum gage in the chamber. This suggests that the pressure during the CNT growth can be reduced by focusing alcohol gas beam effectively. In this study, we carried out CNT growth under high vacuum using a gas source technique with a fine nozzle for the gas introduction in a UHV chamber, and we achieved CNT growth at 10-4 Pa without any excitation processes of carbon source. EXPERIMENT After deposition of Co catalyst (less than 1 nm in thickness) on SiO2(100 nm)/Si substrate by electron beam (EB) evaporation in a UHV chamber, ethanol gas was supplied to the substrate surface through a stainless steel nozzle for 5 hours. During the growth, the samples were heated by a direct electric current. The growth temperature was monitored by a pyrometer, and set between 350 and 900○C by controlling the electrical current. The supply of ethanol gas was controlled by monitoring an ambient pressure, which was set at 1×10-1, 1×10-3 and 1×10-4 Pa. Taking into account the hole area of the nozzle (diameter: 0.5 mm) and the distance between the
tip of the nozzle and the sample (5 mm), the local pressures on the substrate surface wer
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