Delivered by Publishing Technology to: Deakin University Library IP: 75.107.238.136 On: Wed, 16 Mar 2016 12:54:19 Copyright: American Scientific Publishers Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 10, 4074–4077, 2010 Optical Study on Electronic Transport Properties of Single-Walled Carbon Nanotubes at High Temperature Mukhtar Effendi, Hiroyuki Yokoi ∗ , and Noritaka Kuroda Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan The transport properties of single-walled carbon nanotubes (SWNTs) above room temperature are studied in this work. The infrared optical properties of SWNTs were investigated to clarify their con- duction mechanism at high temperature. We present reflectivity spectra of SWNT mats in the infrared region between 0.08 eV and 0.8 eV under Ar gas flow at temperatures between 330 K and 840 K. These spectra have the typical appearance of the metallic reflectivity. Examination within the frame- work of the Drude-Lorentz model was performed to work out the electric resistivity for each reflectivity spectrum. It was found that the resistivity of SWNTs increases superlinearly with increasing the tem- perature from 330 K to 690 K, which can be explained by the quasi-1D metallic term model very well. However, the resistivity at higher temperatures than 690 K exhibited the tendency of saturation and deviated from the quasi-1D metallic term model. This behavior could be attributed to the thermal excitation of free carriers in the semiconducting SWNTs included in the mats. Keywords: Single-Walled Carbon Nanotube Mat, Infrared Optical Spectroscopy, High Temperature Conduction Mechanism, Quasi-One-Dimensional Metallic Term Model, Thermal Excitation of Carriers. 1. INTRODUCTION A single-walled carbon nanotube (SWNT) can be thought of as a graphene sheet rolled into a cylinder labeled with the index (n m) which describes its chirality. Depend- ing on the chirality, SWNTs could exhibit distinct elec- tronic properties, varying from semiconducting ones to metallic. 1 Many interesting properties are expected for this quasi one-dimensional electronic system. However, their transport properties, which are basic electrical prop- erties of SWNTs, are not fully understood although many efforts have been done. 2–12 It has been reported that one- dimensional (1D) variable range hopping (VRH) conduc- tion can be observed in SWNTs aligned in 1 nm sized channels of zeolite crystals. 2 1D VRH in SWNTs seems to be natural because of their quasi-1D structure, but there could be another interpretation whereby the 1D VRH is ascribable to the artificial 1D structure of zeo- lite. Kaiser et al. 5 investigated the resistivity of SWNT mats at low temperature. They suggested that temperature dependence of the resistivity in SWNT mats is given by a simple model of metallic conduction in aligned nanotubes with hopping or tunneling through small electrical barriers, ∗ Author to whom correspondence should be addressed. e.g., tangled regions, inter-rope or intertube contacts, or tubule defects (Eq. (1)).  = AT + B exp  T t T + T s  (1) In this model the resistivity of the total sample is described as the sum of metallic and barrier portions of conduction path. A and B are coefficients which include the geometrical contributions from the effective fractions of the length for the metallic and barrier portions and the fractions for cross-sectional areas of samples. T t is the tem- perature below which the conduction is dominated by the charge carrier tunneling through the barrier. T s denotes the temperature above which the thermal activated conduction over the barrier begins to occur. Shiraishi et al. 7 examined their experimental results on the temperature dependence of electric resistance of SWNT mats below room temperature and found that their results can be explained with both the quasi-one- dimensional (quasi-1D) metallic term model (Eq. (2)) and simple metallic term model (Eq. (1)) quantitatively.  = Q exp  - T m T  + B exp  T t T + T s  (2) In the quasi-1D metallic term model, the metallic term adopted by Kaiser et al. 5 is replaced to a quasi-1D metallic 4074 J. Nanosci. Nanotechnol. 2010, Vol. 10, No. 6 1533-4880/2010/10/4074/004 doi:10.1166/jnn.2010.1975