Boqian Yang

Growth of ZnO nanostructures on metallic and semiconducting substrates by pulsed laser deposition technique

ZnO nanostructures were fabricated on metallic and semiconducting substrates by the pulsed laser deposition technique. Nanoneedles having tips of ~20–50 nm and roots of ~50–100 nm, nanowires with a diameter of 50–70 nm and a length of 5–10 µm and flowers of diameters 1–3 µm with the base of leaves around 150–200 nm were obtained on Si, W and rough Cu substrates, respectively. Growth of nanostructures was explained on the basis of the island growth mechanism. Raman spectroscopy showed that all first order optical normal modes of nanostructured ZnO on W and Cu substrates confirmed the wurtzite structure. Nanoneedles grown on the Si substrate exhibited the absence of two normal modes of A1(LO) and E1(LO) suggesting weak deviation from the wurtzite structure. The field emission from nanoflowers prepared on the Cu substrate exhibited a current density of 1 mA cm−2 at an applied field of 7.2 V µm−1 at ambient temperature, suggesting its utility for flat panel display devices.

Tungsten Oxide Nanorods Array and Nanobundle Prepared by Using Chemical Vapor Deposition Technique

Tungsten oxide (WO3) nanorods array prepared using chemical vapor deposition techniques was studied. The influence of oxygen gas concentration on the nanoscale tungsten oxide structure was observed; it was responsible for the stoichiometric and morphology variation from nanoscale particle to nanorods array. Experimental results also indicated that the deposition temperature was highly related to the morphology; the chemical structure, however, was stable. The evolution of the crystalline structure and surface morphology was analyzed by scanning electron microscopy, Raman spectra and X-ray diffraction approaches. The stoichiometric variation was indicated by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

Structural degradation and optical property of nanocrystalline ZnO films grown on Si (100)

Structural degradation of nanocrystalline ZnO films was observed with an increase in films thickness. Nanocrystalline epitaxial thin film with thickness of ∼170nm changed to polycrystalline ∼900nm with an increase in deposition time. Surface morphology revealed an average grain size of 30–50nm. Spatial correlation model indicated structural disorder due to relative disorientation of crystalline phases at nanoscale. The photoluminescence spectra showed free exciton (FX) ∼3.31eV, donor bound-exciton (DoX) ∼3.26 and donor-acceptor-pair (DAP) ∼3.22eV for thin films, which redshift, i.e., FX ∼3.30, DoX ∼3.24eV, and DAP ∼3.19–3.17eV for thicker films (400–900nm).

Study of the structural evolutions of crystalline tungsten oxide films prepared using hot-filament CVD

Structural evolutions of tungsten oxide(WO3) samples on different substrates are studied using Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The WO3 samples are prepared using hot-filament CVD techniques. The focus of the study is on the evolutions of nano structures at different stages following deposition time. The experimental measurements reveal evolutions of the surface structures from uniform film to fractal-like structures, and eventually to nano particles, and crystalline structures from mono (0 1 0) crystalline thin film to polycrystalline thick film developments. The effect of high temperature on the nanostructured WO3 is also investigated. Well-aligned nanoscale WO3 rod arrays are obtained at a substrate temperature of up to 1400 °C. Further increasing the substrate temperature yields microscale crystalline WO3 particles.

Ambient pressure synthesis of nanostructured tungsten oxide crystalline films

We report the results of the ambient pressure synthesis of tungsten oxide nanowires and nanoparticles on AlN substrates using the hot filament CVD techniques. The morphologic surface, crystallographic structures, chemical compositions, and bond structures of the obtained samples have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and Raman scattering, respectively. Different morphologies were observed for different substrate temperatures, but otherwise identical growth conditions. The experimental measurements reveal the evolutions of the crystalline states and bond structures following the substrate temperatures. Besides, different substrate materials also affected the tungsten oxide nanostructures. Bundles of wire-type tungsten oxide nanowires with a length of up to 5mm were obtained on Al2O3 substrate. Furthermore, the sensitive properties of the super long nanowires to the gas and different temperature were investigated. The dependence of the sensitivity of tungsten oxide nanowires to the methane as a function of the time was obtained. The sensitive properties of the tungsten oxide nanowires have almost linear relationship with the temperature.

Study of temporal current stability and fluctuations of field emitted electrons from ZnO nanostructure films

Stable field emission currents and low fluctuations are important feasibility requirements for the application of materials in field emission devices and displays, more than the low turn on fields that are generally considered. The current stability and current fluctuations of field emitted electrons from ZnO nanostructures were investigated over the period of 2, 12, and 24 h. The films with nanoneedle structure having density around ten/μm2 showed better short and long-term (temporal) stability over a period of 24 h. The short- and long-term stability and the current fluctuations of the nanostructures are reported and the causes for the degradation of the emission current are discussed.