Peter-Xian Feng

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.

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.

Electrical and structural characterizations of one-dimensional carbon nanostructures synthesized at ambient pressure

One-dimensional carbon nanostructures were synthesized at ambient pressure on molybdenum substrates using the pulsed laser deposition techniques. Scanning electron microscopy images revealed the evolutions of the nanostructures for different substrate temperatures, but otherwise identical growth conditions. Transmission electron microscopy images showed that the obtained carbon nanorods were about 20 nm in diameter and 1 µm in length. The crystallographic structures, chemical compositions and bond structures of the carbon materials were investigated using x-ray diffraction, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and Raman scattering spectroscopy, respectively.The electron field emission behaviours of the carbon nanostructures were considerably improved with the increase in substrate temperature. The rod-shaped nanostructures synthesized at 600 °C geometrically increase the effective emission sites, which consequently leads to a high value of field enhancement factor.

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.

Properties of one-dimensional tilted carbon nanorod arrays synthesized by the catalyst-assisted oblique angle deposition technique

One-dimensional tilted carbon nanorod arrays were synthesized on molybdenum substrates by using the catalyst-assisted oblique angle deposition technique. The structures of the one-dimensional tilted carbon nanorods evolve with substrate temperatures, but otherwise identical growth conditions. The crystallographic structures, chemical compositions and bond structures of the tilted carbon nanorods were investigated by using x-ray diffraction, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and Raman scattering spectroscopy. The cross-sectional SEM image showed that multilayered tilted carbon nanorods were also obtained. The electron field emission (FE) behaviours of the obtained one-dimensional carbon tilted nanorod arrays were greatly improved with the increase in substrate temperature. Meanwhile, the sample with multiple layers of carbon tilted nanorods exhibits better FE behaviours than those with single layer.