Zi Qin

Controllable fabrication and electromechanical characterization of single crystalline Sb-doped ZnO nanobelts

We report the fabrication of the high-quality Sb-doped ZnO nanobelts by using a simple chemical vapor deposition method. The nanobelts consist of single-crystalline wurtzite ZnO crystal and grow along [011¯2] direction. An electromechanical system is constructed to explore the transverse electrical properties of a single nanobelt under the different applied loading forces. The I-V results indicate that a little barrier exists in between the nanobelt and the atomic force microscopy tip. An almost linear relationship between the force and the resistance was found at small deformation regions, which demonstrates that the nanobelts have potential applications as force/pressure sensor for measuring the nano-Newton forces.

Electrical bistability and negative differential resistance in single Sb-doped ZnO nanobelts/SiOx/p-Si heterostructured devices

We report the electrical bistability and negative differential resistance (NDR) in single Sb-doped ZnO nanobelts/SiOx/p-type Si heterostructured devices. The current-voltage (I-V) characteristics of the devices were discussed in terms of the energy band diagram of the devices. The origin of the electrical bistability and NDR is suggested to be associated with the electric-field-induced charge transfer. The performance of the fabricated devices can be enhanced under the ultraviolet light illumination.

Controllable synthesis of well-dispersed and uniform-sized single crystalline zinc hydroxystannate nanocubes

Single crystalline zinc hydroxystannate (ZnSn(OH)6) nanocubes have been synthesized on α-{Cu,Sn} copper foils by a low-temperature hydrothermal method. The obtained ZnSn(OH)6 nanocubes have the cubic perovskite crystalline structure and uniform arrangement on the substrate. The possible growth process of the ZnSn(OH)6 crystalline is proposed. The well-dispersed distribution and uniform size of the ZnSn(OH)6 cubes are successfully achieved thanks to the substrate which plays an important role to control the nucleation site and provide Sn4+ ions. The size of the cubes can be adjusted from nanometre to micrometre scale by prolonging the reaction time. After the secondary nucleation, a novel morphology of mother–daughter double cubes was formed. The decomposition of ZnSn(OH)6 cubes annealed at high temperature is also investigated, and interesting hollow-shaped morphology changes are discovered. This method will be useful for the controllable fabrication of nanomaterials and potential applications in nanoscale devices.

High intensity, plasma-induced emission from large area ZnO nanorod array cathodes

High intensity electron emission cathodes based on a well-aligned ZnO nanorod array were fabricated. An investigation of the properties of the plasma and the electron beams produced by ZnO nanorod array cathodes was presented. Intense current electron beams were obtained from the cathodes. At an electric field of 7–8V∕μm and pulse duration of ∼100ns, the highest emission current density reached 76–91A∕cm2. The production mechanism of the electron beams was the plasma-induced emission. The morphology and structure of the ZnO nanorod after the application of the accelerating pulses were characterized. The plasma expanded at a velocity of about 10.7cm∕μs during the pulse interval. Whether the emission currents are high or low, the plasma on the cathode surface were always distributed uniformly. The ZnO nanorod array cathodes are expected to be applied to high power vacuum electronic devices as electron beam sources.

Fast sensitization process of ZnO-nanorod-array electrodes by electrophoresis for dye-sensitized solar cells

A novel electrophoresis based dye adsorption technique is developed for the process of ZnO-nanorod-array dye-sensitized solar cells (DSSC). By applying a constant current electrophoresis procedure, ZnO electrodes were successfully sensitized by N719 dye, and the effects of varying the electrophoretic current and duration time on the performance of DSSC were investigated. It is found that abundant dye adsorption can be obtained within significantly reduced sensitization time by electrophoresis compared to standard immersion method. Thicker ZnO-nanorod-array film and lower electrophoretic current requires longer electrophoresis time to reach the optimal sensitization effect, while very long sensitization time will result in dye agglomeration, which is harmful to the performance of DSSC. The fast dye adsorption process is more advantageous as the ZnO-nanorod-array film becomes thicker because dye molecules can readily penetrate into the depth of ZnO film in a very short time, during which the formation of Zn2+/dye complex can be suppressed.

Investigation on the Plasma-Induced Emission Properties of Large Area Carbon Nanotube Array Cathodes with Different Morphologies

Large area well-aligned carbon nanotube (CNT) arrays with different morphologies were synthesized by using a chemical vapor deposition. The plasma-induced emission properties of CNT array cathodes with different morphologies were investigated. The ratio of CNT height to CNT-to-CNT distance has considerable effects on their plasma-induced emission properties. As the ratio increases, emission currents of CNT array cathodes decrease due to screening effects. Under the pulse electric field of about 6 V/μm, high-intensity electron beams of 170–180 A/cm2 were emitted from the surface plasma. The production mechanism of the high-intensity electron beams emitted from the CNT arrays was plasma-induced emission. Moreover, the distribution of the electron beams was in situ characterized by the light emission from the surface plasma.

Dye-sensitized solar cells with composite ZnO/SnO 2 nanoporous electrodes

Composite nanoporous electrodes made of ZnO/SnO2 nanopowders were fabricated and applied to dye-sensitized solar cells. The morphology and structure of the prepared electrodes was investigated by field emission scanning electron microscope (FE-SEM). It is found that the overall conversion efficiency of DSSCs with composite electrodes was enhanced by almost 32% as compared to DSSCs with pure ZnO electrodes. Adding SnO2 nanopowders to ZnO nanoporous electrodes improved the stability and microstructure of the whole nanoporous electrodes during the dye absorption, thus enhanced the photovoltaic efficiency of the DSSCs based on ZnO nanoporous electrodes.

EFFECT OF LOCALIZED UV IRRADIATION ON TRANSPORT PROPERTY IN ZNO NANOTETRAPOD DEVICES

Semiconductor optoelectronic devices based on a single ZnO nanotetrapod were constructed with Ohmic contact characteristics and the effect of localized UV irradiation on transport property in ZnO nanotetrapod device has been investigated. The measurements for the I-V characteristics and time-resolved measurements of current were conducted. The results indicate that the irradiation under UV light irradiation at the third leg of the tetrapod can readily tune the electrical transport property of the tetrapod along with favorable repeatability and reversibility. The current becomes larger as the UV light power density increases. A probable mechanism has been proposed and discussed. The ZnO nanotetrapod could be potentially used as detectors in irradiation environments.

PREPARATION OF GA-DOPED ZNO NANOROD ARRAYS FOR DYE SENSITIZED SOLAR CELLS APPLICATIONS

Ga-doped ZnO nanorods have been prepared directly on fluorine-doped tin oxide (FTO) by a hydrothermal method at 150C. Crystallization and morphology and effects of Ga doping concentration on efficiency of Dye-sensitized solar cells (DSSCs) were studied by energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), and scanning electron microscopy (SEM). The DSSC using Ga-doped nanorods array exhibited an efficiency of 1.37%, which is much higher than that of DSSC fabricated by undoped ZnO nanorods array. The high energy conversion efficiencies is due to the large carrier concentration in Ga doped ZnO nanorods and high specific surface area of the morphology.

Field Emission Properties of Large Area Carbon Nanotube Cathodes in DC and Pulse Modes

A large area carbon nanotube cathode was fabricated by use of a screen printing method. The emission properties of the cathode were investigated in both direct current and pulse mode experiments. In the direct current mode, the cathode has high field enhancement factor and high emission current density. In the double-pulse mode, the emission current density can approach 267 A/cm at an applied electric field of 15.4 V/um. Steady intense electron beams were obtained from the cathode. The results proved that the emission mechanism of CNTs at pulse electric field is plasma-induced field emission. The carbon nanotube cathode is suitable for not only field emission display applications but also high-power microwave device applications.