Field Emission Properties of BN/C and BN@C Hybrid Nanotubes
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Field Emission Properties of BN/C and BN@C Hybrid Nanotubes Vincent Meunier1,2 , Marco Buongiorno Nardelli1,2 , William Shelton1 , Christopher Roland2 , Jerry Bernholc1,2 , and Thomas Zacharia3 . 1
Center for Computational Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, TN 2 Department of Physics, North Carolina State University, Raleigh, NC 3 Computing and Computational Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN ABSTRACT Our simulations predict that boron-nitride (BN) doping in carbon nanotubes can greatly improve the field emission properties of these systems. The intrinsic electric field associated with the polarity of the B-N bond enhances the emitted current density through a reduction of the work function at the tip. Using a combination of real-space and plane-wave ab initio methods, we show that this effect is present in both coaxial (BN@C) and linear (BN/C) nanotubular assemblies. While in the coaxial geometry the improvement amounts to a factor of five, the current density is predicted to increase by up to two orders of magnitude in BN/C superlattices. INTRODUCTION One decade after their discovery [1], it has been shown that carbon nanotubes possess outstanding potential for their mechanical and electrical properties [2]. The advent of carbon nanotubes, together with recent progress in nanomaterials design and processing, has led to a quest for other novel graphene-based materials with technologically desirable properties. The closely-related boron nitride (BN) nanotubes and mixed BN-C systems [3, 4, 5, 6, 7, 8], which are now produced in macroscopic quantities, have electronic properties that are complementary to pure carbon nanotubes and could therefore be useful in a variety of novel electronic devices. For instance, an early theoretical study predicted that BN/C junctions may well be a practical way to realize stable, nanoscale heterojunctions [9]. In this paper, we investigate BN/C heterojunctions and BN@C coaxial systems using large-scale ab initio simulations [10]. Our calculations show that the polarity of the B-N bond in BN/C heterostructures and related coaxial BN@C systems do dramatically enhance field emission properties, and lead to attractive electronic devices. Although carbon nanotubes are already considered to be good emitters, these desirable properties may be further enhanced by making use of the electronic properties of BN-doped carbon systems. The idea here is to make use of the dipole field as means to reduce the work function at the tips, thereby enhancing the extraction of electrons from the system. The orderly introduction of BN in pure carbon nanotubes may be obtained with two different techniques: either by substituting one CC pair by one BN pair in the hexagonal lattice and therefore mixing the C and BN phases (Fig. 1a), or by creating a system that presents two coaxial homogeneous phases of C and BN (Fig. 1b). The synthesis of pure BN nanotubes through a substitution reaction from a pure C nanotub
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