Kaifu Huo

Extended vapor–liquid–solid growth and field emission properties of aluminium nitride nanowires

Hexagonal AlN (h-AlN) nanowires with an average diameter of around 15 nm have been prepared by an extended vapor–liquid–solid growth technique and characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy and field emission measurements. This preparation is a rather simple route for bulk fabrication of h-AlN nanowires. The promising field emission property observed for h-AlN nanowires points to the important application potential of this material.

Synthesis of single-crystalline α-Si3N4 nanobelts by extended vapour–liquid–solid growth

A simple chemical method for the production of single-crystalline alpha-Si(3)N(4) nanobelts has been developed, consisting of nitridation of a high-Si-content Fe-Si catalyst by ammonia at 1300 degrees C. The as-synthesized product was characterized by means of x-ray diffraction, electron microscopy and energy-dispersive x-ray spectroscopy. The alpha-Si(3)N(4) nanobelts have widths of 60-120 nm, thicknesses of 10-30 nm and lengths up to microns. Four intense green-blue luminescence bands at 398 nm (3.12 eV), 434 nm (2.86 eV), 492 nm (2.52 eV) and 540 nm (2.30 eV) were observed and analysed for the product, which indicates the potential applications in optoelectronics. The growth mechanism has also been speculated upon. The potential technological importance of the product, the simplicity of the preparation procedure, as well as the cheap commercial precursor of Fe-Si alloy particles makes this study both scientifically and technologically interesting.

Synthesis and field emission properties of titanium carbide nanowires

Single crystalline TiC nanowires have been synthesized through a chloride-assisted carbothermal reduction process using active carbon, TiO2 and NaCl powders as precursors and carbon-coated cobalt or nickel nanoparticles as a catalyst. The products were characterized by x-ray diffraction, electron microscopy, energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The TiC nanowires have a face-centred cubic structure with a typical diameter of 20–50xa0nm and a length of up to a few microns. The formation of the product could be well correlated with the characteristic core–shell structure of the catalyst used. The field emission of the TiC nanowires follows the conventional Fowler–Nordheim behaviour and shows a low turn-on field of about 7.1xa0Vxa0µm−1 and good emission stability.

Self-templated synthesis of polycrystalline hollow aluminium nitride nanospheres

Polycrystalline hollow AlN nanospheres with diameters ranging from 20 to 200 nm and shell thickness of about 10 nm were successfully synthesized through the reaction of irregular Al nanopowder with a CH4–NH3 mixture at around 1000 °C by the self-templated method. The products were well characterized by X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy and photoluminescence measurements. The photoluminescence properties of the hollow AlN nanospheres showed the routine blue emissions for AlN nanoparticles as well as an unusual green emission at around 533 nm, indicating the potential for luminescent devices. The synthesis mechanism was reasonably speculated and further supported by the similar synthesis of hollow AlN nanospheres from regular Al particles.

The synthesis of boron nitride nanotubes by an extended vapour?liquid?solid method

An extended vapour?liquid?solid (VLS) growth method, which is the reaction of a mixture of nitrogen and ammonia gas over nanoscale Fe?B catalyst particles at 1100??C, has been developed. With this method, BN nanotubes of diameter about 20?nm have been prepared and well characterized by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. In contrast to traditional VLS growth, the boron component in the BN nanotubes comes from the Fe?B catalyst itself, rather than from the vapour precursor. A growing mechanism has been discussed accordingly.

Chemical synthesis and characterization of boron/boron nitride core–shell nanostructures

A moderate chemical method [i.e., the reaction of diborane (B 2 H 6 ) and a mixture gas of ammonia and nitrogen (NH 3 /N 2 ) over nanoscale iron boride at 1100 °C] was developed to explore the boron nitride (BN) nanostructures. The products were well characterized by high-resolution electron microscopy and energy-dispersive x-ray spectroscopy. Two types of novel core-shell nanocapsules of amorphous boron core encapsulated in crystalline boron nitride shell were obtained. The first one looked like a peanut with an amorphous B core containing a trace of BN crystallites, a transition layer of BN nanofibers and amorphous B, and a thornlike shell of BN nanofibers. The second one looked like a perfect sphere consisting of a pure amorphous B core and a rather smooth crystalline BN shell. These results not only provided us a new chemical method for preparing BN nanostructures but also enriched the important BN nanostructures family. A growth mechanism is also briefly discussed.

Synthesis and field emission characterization of titanium carbide nanowires

Spindt type field emitters are the mature electron sources in application though they have a series of drawbacks, such as expensive production, critical lifetime in vacuum, and high operating voltage. In recent years, carbon nanotubes (CNTs) have demonstrated superior field emission properties and wide potential applications (Bonard et al., 2001). The highlights of CNT have stimulated great interest to explore other one-dimensional (1D) nanomaterials as electron sources. Titanium carbide (TiC), a wide-bandgap semiconductor material, is well known for its high melting point, extreme hardness, and high chemical inertness. Hence, 1D TiC nanostructures could have advantages for field emission. Herein, we present the recent progress about fabrication and field emission characterization of TiC nanowires.

Synthesis and field emission of high pure AlN nanowires

Ever since Spindt field emitter arrays were invented, great efforts have been devoted to explore novel electron sources for better and more reliable performance. In addition to carbon series (diamond films, diamond-like carbon films, carbon nanotubes, and etc.), the one-dimensional (1D) nanostructures of group III nitrides, GaN, AlN, InN and their alloys, are expected to be a kind of promising candidates due to the combination of 1D geometries, small or even negative electron affinity (NEA) and adjustable bandgap which is beneficial for field emission. Our recent study did indicate the good field emission properties of AlN nanowires prepared by the extended vapor-liquid-solid growth (Wu et al., 2003). Herein we report a improved method to fabricate pure AlN nanowires. The white AlN nanowires were produced by the reaction of Al powder and carbon-coated Ni nanoparticles at 1400/spl deg/C and collected from the down-stream of the reaction tube. The products were well characterized by TEM, SEM, XRD and Raman spectrum. The field emission properties of AlN nanowires were measured in a vacuum chamber at a base pressure of /spl sim/1/spl times/10/sup -7/ Torr. The emission current-voltage (I-V) curve were repeatedly measured by a Keithley system for different distances (D) between the sample and anode. The I-V curve qualitatively follow the conventional Fowler-Nordheim behavior according to the straight line plot of log (J/E/sup 2/) versus I/E. The field emission mechanism is also discussed.