Electrical Transport and Confocal Raman Studies of Electrochemically Modified Individual Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWCNTs), due to their excellent structural and electronic properties, [1] have emerged as an attractive material for various applications including molecular electronics [2,3] and field emission devices. [4] A variety of devices have been realized with SWCNTs, such as single electron transistors (SETs) operating at very low temperatures, [5] field-effect transistors (FETs), [6] chemical sensors, [7] and logic circuits. [8] Besides the use of pristine SWCNTs, it has been shown that SWCNTs can be chemically modified, [9±11] a process which, for example, allowed the fabrication of SETs [12] and memory devices [13] operating at room temperature. Electrochemistry is a well-suited tool for controlled modification of SWCNTs. [14] This approach has been followed using both reductive and oxidative coupling schemes, resulting in thin layers of molecules around the SWCNTs.[15] However, little is known about the nature of chemical coupling between the grafted layers and the carbon framework of an individual nanotube, and also about the effect of chemical modification on its electronic properties. Towards this objective, we report in this communication the detailed investigation of individual electrochemically modified SWCNTs. The characterization methods include electrical transport measurements and confocal Raman spectroscopy, both of which can address selected single SWCNTs or bundles. While transport measurements give information about the electronic properties of an individual SWCNT, confocal Raman spectroscopy on individual nanotubes [16] can detect changes of the vibrational properties and hence the disturbances in the lattice structure of an isolated nanotube. These studies were performed separately on metallic and semiconducting SWCNTs, in both cases comparing the effect of the oxidative and reductive coupling schemes. The electrochemical modification (ECM) of individual SWCNTs was performed with 4-aminobenzylamine (A) using the oxidative scheme and with 4-nitrobenzene diazonium tetrafluoroborate (B) employing the reductive scheme. The transport measurements were carried out on the same SWCNTs before and after ECM. Before ECM, the gate dependence of the 2-probe resistance was used to identify a given individual SWCNT as metallic or semiconducting. At room temperature, the unmodified metallic SWCNTs showed a 2-probe resistance in the range 10±25 kX, while the resistance of the semiconducting nanotubes was found to vary between 200 kX and 100 MX among different samples. As control experiments, ECM was performed on selected SWCNTs in the pure electrolyte solution in the absence of A or B. In both cases, neither an increase in height nor a change in the resistance could be detected after modification. Figure 1 summarizes a typical observation made on metallic SWCNTs after oxidative ECM. The SWCNTs were investigated by atomic force microscopy (AFM) before and after ECM to determine the thickness of the grafted layers. The AFM image in Figure 1a shows an individual metallic nanotube contact...

Raman spectroscopy of covalently functionalized single‐wall carbon nanotubes

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Interactions Between Amino Acid‐Tagged Naphthalenediimide and Single Walled Carbon Nanotubes for the Design and Construction of New Bioimaging Probes

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Highly Bendable, Transparent Thin‐Film Transistors That Use Carbon‐Nanotube‐Based Conductors and Semiconductors with Elastomeric Dielectrics

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