Single- and multi-wall carbon nanotube field-effect transistors

Abstract

We fabricated field-effect transistors based on individual single-and multi-wall carbon nanotubes and analyzed their performance. Transport through the nanotubes is dominated by holes and, at room temperature, it appears to be diffusive rather than ballistic. By varying the gate voltage, we successfully modulated the conductance of a single-wall device by more than 5 orders of magnitude. Multi-wall nanotubes show typically no gate effect, but structural deformations-in our case a collapsed tube-can make them operate as field-effect transistors. © 1998 American Institute of Physics. ͓S0003-6951͑98͒00143-0͔Carbon nanotubes ͑NTs͒ are a new form of carbon with unique electrical and mechanical properties.1 They can be considered as the result of folding graphite layers into carbon cylinders and may be composed of a single shell-single wall nanotubes ͑SWNTs͒, or of several shells-multi-wall nanotubes ͑MWNTs͒. Depending on the folding angle and the diameter, nanotubes can be metallic or semiconducting. Simple theory also shows that the band gap of semiconducting NTs decreases with increasing diameter. These predictions have been verified in recent scanning tunneling spectroscopy experiments. 2,3Their interesting electronic structure makes carbon nanotubes ideal candidates for novel molecular devices. Metallic NTs, for example, were utilized as Coulomb islands in single-electron transistors 4,5 and, very recently, Tans and coworkers built a molecular field-effect transistor ͑FET͒ with a semiconducting nanotube. 6In this letter, we report on the fabrication and performance of a SWNT-based FET and explore whether MWNTs can be utilized as the active element of carbon-based FETs. Despite their large diameter, we find that structurally deformed MWNTs may well be employed in NT-FETs. Based on the output and transfer characteristics of our NT devices, we evaluate their carrier density and discuss the transport mechanism.The SWNTs used in our study were produced by laser ablation of graphite doped with cobalt and nickel catalysts. For cleaning, the SWNTs were ultrasonically treated in an H 2 SO 4 /H 2 O 2 solution. MWNTs were produced by an arcdischarge evaporation technique 8 and used without further treatment. The NTs were dispersed by sonication in dichloroethane and then spread on a substrate with predefined electrodes. A schematic cross section of a NT device is shown in Fig. 1. They consist of either an individual SWNT or MWNT bridging two electrodes deposited on a 140 nm thick gate oxide film on a doped Si wafer, which is used as a back gate. The 30 nm thick Au electrodes were defined using electron beam lithography. For imaging, we used an atomic force microscope operating in the noncontact mode. The sourcedrain current I through the NTs was measured at room temperature as a function of the bias voltage V SD and the gate voltage V G . Figure 2͑a͒ shows the output characteristics I -V SD of a device consisting of a single SWNT with a diameter of 1.6 nm for several values of the gate voltage. At V G ϭ0 V, the I -V SD curv...

Carbon Nanotubes for Electronic and Electrochemical Detection of Biomolecules

“…For MWNTs, the large electronic (met-versus sem-) variability of the concentrically nested nanotubes results in significantly lower abundance of semiconducting-only species. Since the first demonstrations of SWNT-FETs by Dekker [89] and Avouris, [90] where p-type semiconductor FET characteristics were observed for carbon nanotubes, a number of nanotube configurations have emerged for efficient detection of a variety of biomolecules, with detection limits down to picomolar (pM) range. [23,91,92] FET-based biomolecular detection has been termed as "label-free" methodology owing to the fact that it does not employ fluorescence, electrochemical, or magnetic tags.…”

“…This causes bending of the conduction and valence bands of the nanotube and forms Schottky barriers at the nanotube/ metal contacts. [101] Because hole (h + ) transport is the dominant conduction pathway in these devices, [90,101] both downward band-bending and the Schottky barrier impede conduction based on the fact that holes prefer to move upwards. A negative V G tends to shift both valence and conduction bands of the SWNT channel upwards (Fig.…”

Photophysics of Individual Single-Walled Carbon Nanotubes

“…In particular, when an electric field passes through a nanotube that is stood on its end, the sharp nanotube tip concentrates the electrons and rapidly projects them onto a target. 50 As circuit miniaturization progresses, SWNTs offer the attractive advantage that they can act as metallic nanowires that have the potential to significantly impact the fields of energy storage 64 and molecular electronics [65][66][67][68][69] ( Figure 1 -5). NDC is observed for metallic nanotubes at low electric fields, which is significant for electronic applications and holds general implications for high-current applications based on 1D materials.…”

Parallel arrays of individually addressable single-walled carbon nanotube field-effect transistors

“…[5][6][7] The feasibility of single-walled carbon nanotube-͑SWNT͒ based electronic devices, such as interconnects 8,9 in molecular electronics, junction rectifiers, [9][10][11] field-effect transistors ͑FETs͒, 12,13 and logic gates, 14 has been demonstrated in recent experiments. More recently, experiments demonstrating the use of SWNTs as the active channel in metal-oxide-semiconductor ͑MOS͒ FETs, which opens the possibility for a wide range of integrated CNT-complementary ͑C͒ MOS nanoelectronics, have also been reported.…”