Yemin Hu

Fabrication, characterization and field emission properties of large-scale uniform ZnO nanotube arrays

Large-scale well-aligned ZnO nanotubes with outer diameters of 100-300 nm and lengths of tens of micrometres have been prepared by a template-based chemical vapour deposition method. The photoluminescence spectrum of the ZnO nanotube arrays consists of a strong violet band at 414 nm, a blue band at 462 nm and a weak shoulder peak at around 480 nm. The field emission of the ZnO nanotube arrays shows a turn-on field of about 7.3 V microm(-1) at a current density of 0.1 microA cm(-2) and emission current density up to 1.3 mA cm(-2) at a bias field of 11.8 V microm(-1).

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.

Synthesis and crystal structure of double-perovskite compound Sr2FeMoO6

Samples of single-phase Sr 2 FeMoO 6 were successfully prepared by solid-state reaction with long sintering times. The crystal structures of the Sr 2 FeMoO 6 samples were determined from X-ray powder diffraction data using the Rietveld refinement method. The structure results obtained by the Rietveld refinements show that an increase in the total sintering time of the solid-state reaction is an effective method to obtain single Sr 2 FeMoO 6 phase and to improve the ordering of Fe and Mo cations (or reducing antisite defects) in the double-perovskite structure. The volume of the tetragonal unit cell of Sr 2 FeMoO 6 contracts slightly after successive sintering treatments. The averaged Fe-O and Mo-O bond lengths as well as the tilt between the FeO 6 and the MoO 6 octahedra decrease with increasing total sintering time. Our results suggest that the detected subtle changes in crystal structure, such as bond lengths and bond angles between the Fe and Mo cations and oxygen, in the ordered double-perovskite structure may be responsible for the large effects on previously reported transport and magnetic properties of an oxide metal.