Quantum Transport Through Intermolecular Nanotube Junctions
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Quantum Transport Through Intermolecular Nanotube Junctions Alper Buldum and Jian Ping Lu Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599 Abstract Quantum transport properties of intermolecular nanotube contacts are investigated. We find that atomic structure in the contact region plays important roles and resistance of contacts varies strongly with geometry and nanotube chirality. Nanotube end-end contacts have low resistance and show negative differential resistance (NDR) behavior. Exerting small pressure/force between the tubes can dramatically decrease contact resistance, if the contact is commensurate. Significant variation and nonlinearity of contact resistance may lead to new device applications.
Impressive progress has been achieved in employing carbon nanotubes for nanoelectronic devices [1-8]. Single-electron transistors [4,5], field effect transistors [6] and rectifying diodes[7] have been reported. Intramolecular nanotube devices have been demonstrated [8] and studied[9]. To further enable such devices and assembles it is clear that nanotube-nanotube contacts will play important roles. Here, we report our studies on contact resistance between nanotubes. We find that atomic scale structure in the contact region is crucial and resistance of contacts varies strongly with geometry and nanotube chirality. Nanotube end-end contacts have low resistance and show negative differential resistance (NDR) behavior. Exerting small pressure/force between tubes can dramatically decrease contact resistance. The significant variation and nonlinearity of contact resistance may lead to new device applications. We study the effect of tube-tube interaction on the transport properties of nanotubes for different positions, orientations and chiralities. Quantum conductance and current-voltage (I-V) characteristics of intermolecular nanotube contacts are investigated using π-orbital tight binding model [10,11] and Landauer-Büttiker formalism with surface Green's function matching method [12-14]. When two nanotubes are brought together interaction between the nanotubes modify the electronic and transport properties. Thus, tube-tube interaction leads to variation of quantum conductance that depends on chirality and local atomic structure in the contact region. For example, in the case of two metallic nanotubes placed in parallel, the interactions broke symmetry and an energy gap may be opened at the Fermi level. Similar effect was found in nanotube bundles [15]. The simplest form of two-terminal nanotube contact is constructed by bringing two tube's end together (Fig. 1(a)). Since the contact (or interaction) region is finite and the tube ends are closed, the junction shows quantum-interference effects. The interference of waves transmitted and reflected from the ends yields resonance structure in conductance (Fig. 1(b)). The number of resonance increases with increasing contact region length, l. This quantum-interference effect introduces Negative Differential Resistanc
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