FET Characteristics of Chemically-Modified CNT
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FET Characteristics of Chemically-Modified CNT R. Kumashiro1, Y. Wang1,2, N. Komatsu1 and K. Tanigaki1,2 1 Department of Physics, Graduate School of Science, Tohoku University, 6-3 Aoba Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan 2 Advanced Institute for Materials Research - World Premier International Research Center, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
ABSTRACT Electric transport properties of chemically modificated carbon nanotubes (CNT) using Sicontaining organic molecules and polymers were investigated by means of the field effect transistors (FET) technique. From the results of FET measurements for each chemically surface modified CNT, it was shown that p-type semiconducting CNT can be converted to n-type ones by physical adsorption of Si-containing organic molecules and polymers having Ph-groups. It is suggested that the electron carrier are doped into CNT from the adsorbed molecules and polymers, and it was also confirmed by the results of adsorption spectra. That is, it can be said that the electronic properties of CNT can be controlled by chemically modifications of outer surface. INTRODUCTION CNT have a bright prospect as electronic materials for nano-scale devices in the future, and a large number of studies have been made in recent years [1-3]. In particular, it is well known that the FET fabricated from CNT having semiconducting properties show high ability in terms of the mobility [4]. However, carriers in pristine CNT are mostly hole, therefore, CNTFET usually show the p-type properties [5]. For applying CNT to electronic devices, it is necessary to control the carriers of both electrons and holes, that is, the electron carrier doping should be established. As electron carrier doping techniques for CNT, three major techniques are generally possible, substitution by hetero carbon atoms, endohedral doping, and exohedral modification. Recently, it has reported that the structural substitution of CNT by hetero carbon atoms, such as group III or V element, changes the electronic properties of CNT [6]. It has been also known that the doping into inner spaces of CNT with alkali metals or organic molecules can change the properties of CNT-FET [7, 8]. Exohedral modifications for CNT by organic reaction have been carried out for the purpose of purification, solubilization, functionalization, and so on [9, 10]. However, a small number of studies have been made relating to the investigation of physical properties. A similar carrier doping could exohedrally be possible when the SWNT surface is chemically modified. With such chemical modifications, the charge transfer from the substituent groups to SWNT will be expected and this could modify the electronic states of SWNT. Recently, we have reported the FET properties of individual SWNT exohedrally modified by Si-containing organic moieties, and demonstrated that p-type nanotubes can be converted to
n-type ones [11, 12]. However, because of ununiformity of the surface-chemical modifications of SWNTs, the t
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