Synthesis, Analysis, and Electrical Property Measurements of Compound Nanotubes in the B-C-N Ceramic System
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Synthesis, Analysis, and Electrical Property Measurements of Compound Nanotubes in the B-C-N Ceramic System
Dmitri Golberg, Yoshio Bando, Pavel Dorozhkin, and Zhen-Chao Dong Abstract Nanotubular structures in the B-C-N ceramic system represent an intriguing alternative to conventional carbon nanotubes. Because of the ability to widely vary the chemical composition of nanotubes within the B-C-N ternary phase diagram and to change the stacking of C-rich or BN-rich tubular shells in multiwalled structures, a wide horizon opens up for tuning nanostructure electrical properties. Pure carbon nanotubes are metals or narrow-bandgap semiconductors, depending on the helicity and diameter, whereas those of BN are insulators with a 5.0 eV gap independent of these parameters. Thus, the relative B/C/N ratios and/or BN-rich and C-rich domain spatial arrangements, rather than tube helicity and diameter, are assumed to primarily determine the B-C-N nanotube electrical response. This characteristic is highly valuable for nanotechnology: while tube diameter and helicity are currently difficult to control, continuous doping of C with BN, or vice versa, proceeds relatively easily due to the isostructural nature of layered C and BN materials. In this article, recent progress in the synthesis, microscopic analysis, and electrical property measurements of a variety of compound nanotubes in the ceramic B-C-N system is documented and discussed. Keywords: ceramic nanostructures, electrical properties, nanotubes, transmission electron microscopy (TEM).
Introduction Soon after the identification of the carbon nanotube (CNT),1 boron nitride nanotubes were theoretically predicted2 and subsequently synthesized.3 BN nanotubes are 38
more thermally and chemically stable than those of carbon through inheriting the relevant properties of layered BN and graphite.4 In addition, while CNTs are
metallic or semiconducting depending on helicity (i.e., the crystallographic orientation of the graphitic-sheet wrapping axis to the tube axis), diameter, and the number of tubular shells,5 those of BN have been predicted to be insulating, independent of these difficult to control parameters.2 The ternary B-C-N system presents an exciting opportunity to prepare ceramic nanotubes of various compositions ranging from pure C to pure BN.6,7 Filmlike bulk B-C-N materials have been known for a decade,8 but large-scale synthesis of ternary B-C-N nanotubes has lingered far behind. Nanotubes may be advantageous materials in many fields. Reinforcing fibers, flat-panel display emitters, field-effect transistors, portions of complex electronic networks and ultralight hydrogen-storage containers are only a few of many promising nanotube applications.9 This wide range of nanotube-based devices arises from their ultrahigh aspect ratio, superior strength, and nanoscale diameters. The thermal conductivity of nanotubes has also been theoretically predicted to be superior even to that of diamond, making them highly promising for the cooling units for the new generation of ultra
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