Electron Transport in Single-Walled Carbon Nanotubes
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Electron Transport
where L is the tube length. The total resistance is approximately the sum of these three contributions: R h4e2 Rc Rt.
in Single-Walled Carbon Nanotubes
(4)
In the following, we will discuss the resistance of SWNT devices at room temperature in terms of these contributions. At low temperatures, SWNT devices exhibit a number of interesting quantum phenomena, but we refer the reader to existing reviews for a discussion of these topics.7,10,11 To make devices, nanotube growth and deposition techniques (described in the article by Liu et al. in this issue) are combined with semiconductor processing technologies. An example is shown in Figure 1. Source and drain electrodes allow the conducting properties of the nanotube to be measured, and a third gate electrode is used to control the carrier density on the tube. When the conductance of the tube is measured as the gate voltage is varied, two classes of behavior are seen. In
Paul L. McEuen and Ji-Yong Park Abstract Single-walled carbon nanotubes (SWNTs) are emerging as an important new class of electronic materials. Both metallic and semiconducting SWNTs have electrical properties that rival or exceed the best metals or semiconductors known. In this article, we review recent transport and scanning probe experiments that investigate the electrical properties of SWNTs. We address the fundamental scattering mechanisms in SWNTs, both in linear response and at high bias. We also discuss the nature and properties of contacts to SWNTs. Finally, we discuss device performance issues and potential applications in electronics and sensing. Keywords: electron transport, phonon scattering, single-walled carbon nanotubes, scanning probe.
Introduction Single-walled carbon nanotubes (SWNTs) are nanometer-diameter cylinders consisting of a single graphene sheet wrapped up to form a tube. They were discovered in the early 1990s,1,2 and the first electrical measurements on individual tubes were performed in 1997–1998.3–5 Since then, a huge number of papers have been written on their electrical properties, including a number of excellent reviews.6–8 Both experiments and theory have shown that SWNTs can be either metals or semiconductors, and their electrical properties can rival, or even exceed, the best metals or semiconductors known. In this article, we give a brief update on the status of the field of SWNT electronics. The data presented here are taken from work in which the authors were collaborators, but they are representative of the field. The remarkable electrical properties of SWNTs stem from the unusual electronic structure of the two-dimensional (2D) material graphene. It has a bandgap in most directions in k-space, but has a vanishing bandgap along specific directions and is called a zero-bandgap semiconductor. When wrapped to form a SWNT, the momentum of the electrons moving around the circumference of the tube is quantized. The result is either a one-dimensional (1D) metal or semiconductor, depending on how 272
the allowed momentum states compare
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