Guangping Zhu

Two-photon excited whispering-gallery mode ultraviolet laser from an individual ZnO microneedle

Wurtzite structural ZnO microneedles with hexagonal cross section were fabricated by vapor-phase transport method and an individual microneedle was employed as a lasing microcavity. Under excitation of a femtosecond pulse laser with 800 nm wavelength, the ultraviolet (UV) laser emission was obtained, which presented narrow linewidth and high Q value. The UV emission, resonant mechanism, and laser mode characteristics were discussed in detail. The results demonstrated that the UV laser originated from the whispering-gallery mode induced by two-photon absorption assisted by Rabi oscillation.

Growth and spectral analysis of ZnO nanotubes

ZnO nanotubes were fabricated by vapor-phase transport using the mixture of ZnO and graphite powders in air. A self-catalyzed growth mechanism was proposed based on microstructure analysis by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Raman scattering, integrated photoluminescence, and time-resolved photoluminescence were employed to explore the optical properties and the dynamic process. Combing with crystal structure and the spectral characteristics of the ZnO nanotubes, the charge carrier transport process was discussed.

Hydrothermally grown ZnO nanorods on self-source substrate and their field emission

Vertically aligned zinc oxide nanorod arrays were grown directly using a zinc foil as both source and substrate in pure water at low temperature by a simple hydrothermal reaction. The morphology and crystal structure of the ZnO nanorod arrays were examined by scanning electron microscopy, transmission electron microscopy and x-ray diffraction, respectively. The nanorods grew along the [0?0?0?1] direction and were 80?nm in diameter and almost 2??m in length. Directly employing the zinc foil substrate as cathode, the field emission (FE) of the ZnO nanorods presented a two-stage slope behaviour in a ln(J/E2)?1/E plot according to the Fowler?Nordheim equation. The FE behaviour was investigated by considering the action of the defects in ZnO nanorods based on the measurement of the photoluminescence.

Zinc oxide hexagram whiskers

Through vapor-phase transport method, zinc oxide hexagram whiskers with uniform size and morphology were fabricated by heating a mixture source of zinc oxide, indium oxide, and graphite powders in air. Each whisker presented a hexagonal disk core closed by six equivalent surfaces of {101¯0} and was surrounded by side nanorods grown along the diagonal of the core disk in the 6-symmetric directions of ±[112¯0], ±[21¯1¯0], and ±[12¯10]. Based on the vapor-liquid-solid mechanism, the growth process of the zinc oxide hexagrams were discussed by considering the thermal dynamic properties of zinc oxide and indium oxide.

Electrochemically deposited zinc oxide arrays for field emission

Periodic zinc oxide rod arrays were fabricated on patterned templates by electrochemical deposition and were employed as field emitters. The morphology and crystal structure of the zinc oxide array were examined by scanning electron microscopy and x-ray diffraction, respectively. The dependence of the field emission current density J and the applied electric field E presented a two-stage slope behavior in ln(J∕E2)−1∕E plot according to Fowler-Nordheim equation. The mechanism of the electron emission is attributed to the defects in the electrochemically deposited zinc oxide rods.

Dielectrophoretic assembly of ZnO nanowires

The synthesis of zinc oxide (ZnO) nanowires is achieved by vapor phase transportation (VPT) method. The designed quartz tube, whose both ends are narrow and the middle is wider, is used to control the growth of ZnO nanowires. Dielectrophoresis (DEP) method is employed to align and manipulate ZnO nanowires which are ultrasonic dispersed and suspended in ethanol solution. Under the dielectrophoretic force, the nanowires are trapped on the pre-patterned electrodes, and further aligned along the electric field and bridge the electrode gap. The dependence of the alignment yield on the applied voltage and frequency is investigated.

Patterned growth of ZnO nanofibers

A simple method is adopted to grow ZnO nanofibers laterally among the patterned seeds designed in advance on silicon substrate. The preparation of seed lattices is carried out by lithographing the metal zinc film evaporated on the substrate. A layer of aluminum is covered on the zinc layer to prevent the ZnO nanorods vertically growing on the top surface. After oxidation, the patterned ZnO/Al2O3 spots are formed at the sites for the horizontal growth of ZnO nanofibers by the vapor phase transportation (VPT) method using the zinc powders as source material.

Optical function of bionic nanostructure of ZnO

A novel bionic network nanostructure of zinc oxide (ZnO), which is similar to the microstructure of a butterfly wing, was first fabricated by a vapor-phase transport method using zinc powder as a source. These bionic nanostructures are composed of three ordered multi-aperture gratings. Similar to the optical effect of butterfly wings, the diffraction patterns of the bionic network of ZnO were observed. The mechanism of the optical function was discussed based on the physical model of multi-aperture diffraction.

Field Emission from ZnO by Morphological and Electronic Design

In this paper, field emission from ZnO was studied by morphological and electronic design. By fabricating ZnO into nanopin structure with sharp tip, we can obtain low threshold and high emission current density. By doping ZnO with gallium, we can lift up the Fermi level and increase the conductivity to enhance the field emission. The fabrication of nanostructures and analysis of field emission will be discussed.