Junqing Hu

Bio: Junqing Hu is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Nanocrystalline material & Transmission electron microscopy. The author has an hindex of 7, co-authored 13 publications receiving 728 citations.

Thermal Reduction Route to the Fabrication of Coaxial Zn/ZnO Nanocables and ZnO Nanotubes

Abstract: Coaxial Zn/ZnO nanocables and ZnO nanotubes have been fabricated via a thermal reduction route using ZnS powder as the source material. The samples were characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectrometry. The as-synthesized Zn/ZnO nanocables consisted of a metallic core (Zn) ≈50 nm in diameter and a semiconductor outer shell (ZnO) ≈5 nm in thickness and several micrometers in length. A good epitaxial relationship between the Zn core and ZnO shell was observed, and misfit dislocations were observed at the Zn/ZnO interface, which accommodated the relatively large lattice mismatch. The outer diameter and wall thickness of the ZnO nanotubes are ≈60 and ≈10 nm, respectively. The possible formation mechanisms for the Zn/ZnO nanocables and ZnO nanotubes are discussed.

Growth of sic nanorods at low temperature

Abstract: Cubic-phase SiC (β-SiC) nanorods were synthesized through a one-step reaction under pressure at 400 °C by which the crystalline product can be obtained directly without annealing at high temperature. The reaction was carried out in an autoclave by using SiCl4 and CCl4 as reactants and metal Na as coreductant. The x-ray diffraction pattern indicates the formation of β-SiC and x-ray photoelectron spectra display the stoichiometric relation between Si and C. Transmission electron microscopy images reveal that the product consists of nanorods with diameters from 10 to 40 nm and lengths up to several micrometers.

Synthesis of β-Ga2O3 Nanowires by Laser Ablation

Abstract: A simple laser ablation method has been employed for the synthesis of β-Ga2O3 nanowires. The as-synthesized products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and room-temperature photoluminescence. The synthesized β-Ga2O3 nanowires have diameters of 15−50 nm and lengths up to several micrometers, and a few of the nanowires appear to have ring-shaped structures. Photoluminescence of the bulk β-Ga2O3 nanowires shows a stable and broad green emission band centered at 497 nm, which has a blueshift of 30 nm from β-Ga2O3 powder. Possible growth mechanisms of the β-Ga2O3 nanowires are briefly discussed.

A review of Ga2O3 materials, processing, and devices

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Growth of nanowires

Abstract: The tremendous interest in nanoscale structures such as quantum dots (zero-dimension) and wires (quasi-one-dimension) stems from their size-dependent properties. One-dimensional (1D) semiconductor nanostructures are of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. For 1D semiconductor nanomaterials to have wide practical application, however, several areas require further development. In particular, the fabrication of desired 1D nanomaterials with tailored atomic structures and their assembly into functional devices are still major challenges for nanotechnologists. In this review, we focus on the status of research on the formation of nanowire structures via highly anisotropic growth of nanocrystals of semiconductor and metal oxide materials with an emphasis on the structural characterization of the nucleation, initial growth, defects and interface structures, as well as on theoretical analyses of nanocrystal formation, reactivity and stability. We review various methods used and mechanisms involved to generate 1D nanostructures from different material systems through self-organized growth techniques including vapor–liquid–solid growth, oxide-assisted chemical vapor deposition (without a metal catalyst), laser ablation, thermal evaporation, metal-catalyzed molecular beam epitaxy, chemical beam epitaxy and hydrothermal reaction. 1D nanostructures grown by these technologies have been observed to exhibit unusual growth phenomena and unexpected properties, e.g., diameter-dependent and temperature-dependent growth directions, structural transformation by enhanced photothermal effects and phase transformation induced by the point contact reaction in ultra-thin semiconductor nanowires. Recent progress in controlling growth directions, defects, interface structures, structural transformation, contacts and hetero-junctions in 1D nanostructures is addressed. Also reviewed are the quantitative explorations and predictions of some challenging 1D nanostructures and descriptions of the growth mechanisms of 1D nanostructures, based on the energetic, dynamic and kinetic behaviors of the building block nanostructures and their surfaces and/or interfaces.