B-C-N Nanotubes and Related Nanostructures

B–C–N is an emerging material system consisting of novel nanostructures of boron (B), carbon (C), boron nitride (BN), carbon nitride (CN _x ), boron-carbon nitride (B _x C _y N _z ), and boron carbide (B _x C _y ). These B–C–N materials are sometimes called as frontier carbon materials, because of their flexibility in forming materials of various types of hybridizations similar to those in the pure carbon system. This chapter provides a concise introduction on all these materials. Readers are referred to various references and other chapters compiled in this book for further reading.

This chapter provides a comprehensive review on the current research status of boron nitride nanotubes (BNNTs), especially the multiwalled nanostructures. Experimental and theoretical aspects of the properties, synthesis, and characterization of BNNTs, as well as their potential mechanical, electronic, chemical, and biological applications are compiled here.

In this chapter, we review the current status of research on heteroatomic single-walled nanotubes (SWNTs): boron nitride (BN), B–C, C–N, and B–C–N. We present developments in the synthesis, the characterization, and the properties measurements and theoretical studies. These nanotubes have unique properties when compared with that of their carbon counterparts. For instance, BN-SWNTs are chemically inert, resistant to oxidation at high-temperature, and most importantly, possess a uniform electronic structure that is independent of their geometry. In the first part of this chapter, we review the different synthesis methods employed to produce these nanotubes (high and medium-low temperature processes). We then turn to the study of the atomic structure of these nanomaterials by different transmission electron microscopy techniques as well as we review the works concerning the growth mechanism of these nanotubes. Finally, the main physical (electronic, vibrational, optical, mechanical, electromechanical, and thermal) and chemical (functionalization and hydrogen storage) properties of these heteroatomic SWNTs, particularly the case of BN, are outlined, followed by the presentation of the potential applications of these nanoobjects.

We review in the present chapter the electronic and optical properties of hexagonal boron-nitride and hexagonal composite boron carbonitride planar and nanotubular structures. We focus mainly on theoretical aspects, but illustrate in all situations the link with existing experimental findings. In a first part, the ­insulating nature, and the band gap stability, of boron-nitride nanotubes are shown to be related to the ionicity character of the boron-nitrogen bond. Specific ­emphasis is given to the optical properties and the related excitonic effects. In a second part, the evolution of the stability and band gap of boron carbonitride systems as a function of the degree of segregation in pure carbon or boron-nitride domains is illustrated and their potential in terms of rectifying hetero-junctions, quantum dots, or ­visible-light optoelectronics devices is emphasized.

As for carbon nanotubes, optical and vibrational spectroscopy – in particular Raman and luminescence spectroscopy – play an important role for the characterization of BN nanotubes. In this chapter we review, from a theoretical view point, the different spectroscopic techniques that are currently used for BN nanotubes and make a close link with available experimental data. We summarize experimental and theoretical data on optical absorption spectroscopy, luminescence spectroscopy, electron-energy loss spectroscopy, Raman spectroscopy, and infrared (IR) absorption spectroscopy. The combination of all those methods allows for a fairly complete characterization of the electronic structure and the vibrational properties of BN tubes. Possible applications in optoelectronic devices are briefly discussed.

Various types of boron nitride (BN) nanostructured materials such as nanocage clusters, nanotubes, nanohorns, nanoparticles, and nanocapsules were synthesized by arc melting, thermal annealing, and chemical vapor deposition methods, which were characterized by high-resolution electron microscopy and molecular orbital calculations, and their properties were discussed. The BN clusters consisted of 4-, 6-, 8- and 10-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. Total energy calculation showed that some elements stabilize and expand the B₃₆N₃₆ structure. Bandgap energies of the B₃₆N₃₆ clusters were found to be reduced by introducing a metal atom inside the cluster, which indicates controllability of the energy gap. Chiralities of BN nanotubes with zigzag- and armchair-type structures were directly determined from high-resolution images, and structure models are proposed. Total energies of BN nanotubes with a zigzag-type structure were lower than those of armchair-type structure, and these results agreed well with the experimental data. Cup-stacked BN nanotubes and Fe-filled BN nanotubes were also produced, and the atomic structures, structural stability, and electronic property were investigated and discussed. BN nanohorns were synthesized, and multiwalled BN nanohorns would be stabilized by stacking of BN nanohorns. Formation and structures of multiply twinned nanoparticles with fivefold symmetry in chemical vapor-deposited BN were also investigated. A new process for Fe or Co nanoparticles coated with BN layers in large quantity was developed, and they exhibited a soft magnetic characteristic and good oxidation resistances. These unique structures would be suitable materials for nanoelectronics devices, magnetic recording media, and biological sensors with excellent protection against oxidation and wear. Possibility of hydrogen gas storage in BN clusters was also investigated by molecular orbital calculations, which indicated possibility of hydrogen storage of ~5 wt%. The new BN nanostructured materials would be expected as future nanocale devices.

This chapter is devoted to carbon nitride and boron carbon nitride nanostructures, an important and indispensable member in the family of nanomaterials for various applications, especially in nanoelectronics. It covers all the main aspects of the current research on the carbon nitride and boron carbonitride nanostructures. The attention is mainly focused on the one-dimensional carbon nitride and boron carbon nitride nanotubes. The most critical issues were addressed from the perspectives of synthesis, composition, structure, property, and application. Due to the presence of multielements in graphite-like layers, the carbon nitride and boron carbon nitride nanotubes display much richer diversities than their carbon counterparts in structure and property. The carbon nitride nanotubes behave always as metallic wires, and the boron carbon nitride nanotubes exhibit semiconducting properties tailorable in a large range depending only on compositions. The properties of electrical conducting, electron field emission, photoluminescence, hydrogen storage, and lithium storage are also presented in this chapter based on the current knowledge.

Carbon nanotubes are very stable systems having a considerable chemical inertness due to the strong sp ² hybridized covalent carbon bonds on their surface. However, various applications of carbon nanotubes require their doping or ­chemical modification through the addition of atoms and/or molecules (covalently or ­noncovalently) in order to alter their physicochemical properties. In this chapter we review the importance of different types of doping in carbon nanotubes (single, double, and multiwalled). Regarding the location of the dopant species within the nanotubes, it is possible to classify the doping process as being exohedral ­(intercalation), endohedral (filling), and in-plane (replacing carbon atoms). The effects of doping on the electronic, vibrational, chemical, magnetic, and mechanical properties are discussed by analyzing the experimental results obtained with different spectroscopic techni­ques such as resonant Raman, X-ray photoelectron (XP), electron energy loss, and others. Applications of doped-carbon nanotubes are also summarized.

Owing to the rapid developments related to the novel B _x C _y N _z ternary structures, the pedagogical review chapter has several antecedents as new results have emerged. Specifically, we will focus on the B _x C _y (with x, y ;= ;0–1) hybrid material where the qualitative trend, in general, can be described by the ratio of its constituents. There is, however, a significant asymmetric popularity between the boron and carbon in the scientific literature. Carbon-based structures are well studied compared with boron-based structures. Consequently, understanding of the role played by boron in the formation of the B _x C _y hybrid structures remains somewhat incomplete. We, therefore, devote a substantial part of discussion on the boron-related structures with an aim to achieve the goal of a complete understanding of the physics and chemistry of the hybrid B _x C _y material.