Dingqu Wang

Controlled assembly of zinc oxide nanowires using dielectrophoresis

A structure similar to a field effect transistor with two isolated top electrodes comprising the source and drain and a lower substrate electrode as the gate was used for the dielectrophoresis-based assembly of zinc oxide nanowires. The results reveal that the assembly of nanowires is significantly affected by the gap distance between the two top electrodes as well as the magnitude and frequency of the applied electric field. Gate assisted assemblies using direct current and alternating current dielectrophoresis were also investigated and determined to improve the assembly effect of nanowires.

Piezoelectric characterization of a single zinc oxide nanowire using a nanoelectromechanical oscillator.

In this paper, we present a nanoelectromechanical oscillator with a single semiconducting zinc oxide nanowire (ZnO) doubly clamped and suspended on two metal electrodes by which the piezoelectric property on the growth of the ZnO nanowire along the c-axis, [0001], is characterized by the resonant frequency shift of the oscillator. We report that the resonance of the nanowire oscillator can be detected in ambient air and the effective piezoelectric coefficient on the growth of a ZnO nanowire along the c-axis, [0001], is significantly larger than that of bulk (0001) ZnO.

Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

We have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

Single semiconducting zinc oxide nanowire based device for thermal and airflow sensing

This paper reports a technology for fabricating a novel nanostructure-based device comprised of a single semiconducting zinc oxide (ZnO) nanowire suspended between two micro Au electrodes for sensor applications. The electric characteristics of the device before and after processed by Pt deposition using focused ion beam microscope were comparatively studied. Furthermore, the potential applications by using the device for thermal and airflow sensing were also investigated. The temperature coefficient of resistance of the ZnO nanowire was estimated to be about -2.61 times 10-3degC-1. The airflow sensitivity of the device is about 3 kOmega/m/s. Compared with conventional sensors, this device takes advantages of high sensitivity and ultra-low power.

Modeling and experimental study of nanoelectromechanical oscillator using single zinc oxide nanowire

This paper reports a novel nanoelectromechanical oscillator using a single zinc oxide (ZnO) nanowire suspended across two micromachined Au electrodes. The oscillator is self-driven into a motion that is self-detected by using a field effect transistor (FET) configuration and a lock-in detection method. A continuum electromechanical model is established to realize a theoretical analysis on the oscillator and the primary experimental measurements are performed to validate the effectiveness of the device. Compared with other nanoelectromechanical oscillators, such as that with carbon nanotubes, the oscillator based on ZnO nanowire is provided with an enhanced electromechanical response and an observable resonance with a frequency on the order of tens of megahertz driven in an air environment. These merits significantly enhance the devices practicability. The device can be potentially applied for actuators and sensors.

Current-voltage and Optoelectronic Properties of Semiconducting ZnO Nanobelts

We report on electrophoretic alignment of ZnO nanobelt bunches and their electrical and optical properties. The nanobelts were trapped onto a pair of electrodes by using alternating electrical current at frequency between 5 ~ 50 MHz and peak-to-peak amplitude from 2 to 20 V. Their electrical transport properties associated with the photoelectricity were studied at room temperature in the air ambient by using a xenon arc lamp source. Three typical IV characteristics were observed: asymmetry, symmetry and infinite impedance. The photoconductivity measurements show that the photocurrent through ZnO nanobelts increases as about 1.6 power of light intensity. The electron concentration Delta n is estimated to be 3.3times107 cm-1 at a bias voltage of -3V. Photocurrent decay was also studied through the experiment of photoresponse to illumination, and the decay time was estimated to be about 3 s. Collectively, ZnO nanobelts are demonstrated to be a remarkable optoelectronic material that holds wide applications for nanoscale photonic devices.

Design of a Hybrid Micro/Nano Cantilever-based Resonant Sensor and its Fabrication Method

Due to novel mechanical and electrical properties of nanomaterials, such as carbon nanotubes and semiconducting oxide nanobelts, utilizing nanomaterials in micro electromechanical structure to improve performances of sensors has attracted many interests. In this paper, we report a novel micro/nano cantilever structure applying to sense accelerations based on resonant detection. The structure is comprised of a seismic micromachined inertial mass supported by two parallel ZnO nanobelts as doubly-clamped nano-cantilevers suspending between two metal electrodes located over a micromachined trench. Another bottom electrode located underneath the mass is utilized to apply electrostatic force on the mass. The acceleration normal to the mass plane induces electrostatic stiffness change and, in turn, a change in the resonant frequency. We propose design and an effective fabrication for this sensor structure.