Ju Gao

Bio: Ju Gao is an academic researcher from University of Hong Kong. The author has contributed to research in topics: Nanorod & Transmission electron microscopy. The author has an hindex of 3, co-authored 4 publications receiving 172 citations.

Simple technique for bulk quantity synthesis of ZnO tetrapod nanorods

Abstract: In this work, we report a simple method for mass production of ZnO tetrapod nanorods. A mixture of Zn and graphite powders (ratio 2:1) was placed in a quartz tube. The quartz tube was placed in a horizontal tube furnace and heated up to 950°C. The tube was then removed from the furnance and quenched to room temperature. Fluffy products white in color were formed on the walls of the tube. Obtained products were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence. SEM images showed tetrapod-like ZnO nanorods. The four tetrapod legs were approximately equal in length, and the length of tetrapod legs was in the range ~1-3 μm. We investigated influence of the growth temperature (in the range from 700°C to 1100°C) and Zn to catalyst ratio to the properties of obtained products. Fabrication is different atmospheres (air, argon, nitrogen, humid argon, and humid nitrogen) was also performed. The influence of growth conditions (temperature, atmosphere, and catalyst concentration) to the formation and properties of ZnO nanorods is discussed.

One-Dimensional Metal-Oxide Nanostructures: Recent Developments in Synthesis, Characterization, and Applications

Abstract: 1D metal-oxide nanostructures have attracted much attention because metal oxides are the most fascinating functional materials. The 1D morphologies can easily enhance the unique properties of the metal-oxide nanostructures, which make them suitable for a wide variety of applications, including gas sensors, electrochromic devices, light-emitting diodes, field emitters, supercapacitors, nanoelectronics, and nanogenerators. Therefore, much effort has been made to synthesize and characterize 1D metal-oxide nanostructures in the forms of nanorods, nanowires, nanotubes, nanobelts, etc. Various physical and chemical deposition techniques and growth mechanisms are exploited and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the 1D metal-oxide nanostructures. Here a comprehensive review of recent developments in novel synthesis, exceptional characteristics, and prominent applications of one-dimensional nanostructures of tungsten oxides, molybdenum oxides, tantalum oxides, vanadium oxides, niobium oxides, titanium oxides, nickel oxides, zinc oxides, bismuth oxides, and tin oxides is provided.

Defect emissions in ZnO nanostructures

Abstract: Defects in three different types of ZnO nanostructures before and after annealing under different conditions were studied. The annealing atmosphere and temperature were found to strongly affect the yellow and orange-red defect emissions, while green emission was not significantly affected by annealing. The defect emissions exhibited a strong dependence on the temperature and excitation wavelength, with some defect emissions observable only at low temperatures and for certain excitation wavelengths. The yellow emission in samples prepared by a hydrothermal method is likely due to the presence of OH groups, instead of the commonly assumed interstitial oxygen defect. The green and orange-red emissions are likely due to donor acceptor transitions involving defect complexes, which likely include zinc vacancy complexes in the case of orange-red emissions.

Self-Organization of Bidisperse Colloids in Water Droplets

Abstract: Most of the colloidal clusters have been produced from oil-in-water emulsions with identical microspheres dispersed in oil droplets. Here, we present new types of binary colloidal clusters from phase-inverted water-in-oil emulsions using various combinations of two different colloids with several size ratios: monodisperse silica or polystyrene microspheres for larger particles and silica or titania nanoparticles for smaller particles. Obviously, a better understanding of how finite groups of different colloids self-organize in a confined geometry may help us control the structure of matter at multiple length scales. In addition, since aqueous dispersions have much better phase stability, we could produce much more diverse colloidal materials from water-in-oil emulsions rather than from oil-in-water emulsions. Interestingly, the configurations of the large microspheres were not changed by the presence of the small particles. However, the arrangement of the smaller particles was strongly dependent on the n...