Controlled synthesis of quasi-one-dimensional boron nitride nanostructures
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A floating catalyst chemical vapor deposition method was developed for the synthesis of quasi-one-dimensional (1D) boron nitride (BN) nanostructures. By carefully tuning the experimental parameters such as growth temperature, floating catalyst concentration, and boron precursor, high quality 1D BN nanostructures including nanotubes, nanobamboos, and nanowires were selectively produced. The microstructures of the obtained 1D BN nanomaterials were characterized, and it was found that the nanostructures are composed of hexagonal BN phase with (002) planes stacking in different manners. A growth mechanism of the BN nanostructures was proposed based on the analysis of their structural characteristics and growth conditions.
I. INTRODUCTION
One-dimensional (1D) boron nitride (BN) nanostructures have attracted much attention for their novel structures, interesting properties, and potential applications. They are uniform semiconducting materials,1,2 which makes them favorable for some electronic applications. The negative electron affinity (NEA)3 surface of h-BN indicates that BN nanostructures can be excellent field emitters. In addition, they are chemically stable, mechanically tough, and highly resistant to oxidation.4 Therefore, 1D BN nanostructures can be promising candidates for the reinforcement phase in composites, especially for those used in severe environments. Moreover, it was reported that BN nanotubes are excellent piezoelectric5 materials with response values higher than those of piezoelectric polymers. The properties of low-dimensional materials strongly depend on their structural characteristics, such as size, shape, and surface states. Thus controllable production of 1D BN nanostructures is important, for both the investigation of their fundamental properties and the exploration of their practical applications. Much attention has been paid to the synthesis of BN nanotubes.6–8 Chen et al.9 reported a solid-state ball-milling process for bulk production of BN nanotubes. Also, mass production of BN nanotubes up to the kilogram level was achieved by this method.10 It was reported recently that large-scale production of BN nanotubes could be achieved11 by using B, FeO, and MgO as boron precursors reacting with
II. EXPERIMENTAL SECTION A. Chemicals
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0350 J. Mater. Res., Vol. 22, No. 10, Oct 2007
http://journals.cambridge.org
N2 in an inducing furnace at high temperature. Onedimensional BN nanobamboos12,13 and nanowires14–17 have received far less attention, although their distinct structure may have interesting properties and potential applications different from those of BN nanotubes.13,17 However, the large-scale synthesis of these nanostructures is still a challenge. Our motivation in this study was to develop a synthesis technique by which various 1D BN nanostructures can be selectively prepared in an efficient way. We know that carbon nanotubes (CNTs) possess a structure analogous to that of BN nanotubes.18 Our pr
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