Zengze Wang

Size Dependence of Dielectric Constant in a Single Pencil-Like ZnO Nanowire

Scanning conductance microscopy (SCM) is used to measure the dielectric constant of a single pencil-like zinc oxide (ZnO) nanowire with the diameters ranging from 85 to 285 nm. As the diameter decreases, the dielectric constant of ZnO nanowire is found to decrease from 6.4 to 2.7, which is much smaller than that of the bulk ZnO of 8.66. A core-shell composite nanowire model in terms of the surface dielectric weakening effect is proposed to explore the origin of the size dependence of dielectric constant, and the experimental results are well explained.

Piezotronic interface engineering on ZnO/Au-based Schottky junction for enhanced photoresponse of a flexible self-powered UV detector.

Exploiting piezoelectric effect to engineer material interface has been confirmed as a promising way to optimize the performance of optoelectronic devices. Here, by using this effect, we have greatly improved the photoresponse of the fabricated ZnO/Au Schottky junction based self-powered UV detector. A 440% augment of photocurrent, together with 5× increased sensitivity, was obtained when the device was subjected to a 0.580% tensile strain. The enhancement can be attributed to the facility separation and extraction of photoexcites due to the formation of the stronger and expanding built-in field, which is a result of charge redistribution induced by piezoelectric polarization at the ZnO/Au interface. This study not only can strengthen the understanding of piezoelectric effects on energy devices but also can be extended to boost performances of optoelectronic devices made of piezoelectric semiconductor materials.

Size effect in a cantilevered ZnO micro/nanowire and its potential as a performance tunable force sensor

Multi-axis force sensing in the nanonewton range is essential in M/NEMS, intelligent electron devices, and structure monitoring areas. Here a nanonewton force sensor with tunable performances based on a cantilevered ZnO micro/nanowire has been fabricated. Owing to the modification effect of the strain induced piezopotential on the carrier transport at the M/S interface, the force can be linearly related to the natural logarithm of the current. More importantly, through changing the position of the applied force along the c-axis direction of the ZnO wire, which can also be regarded as the size effect of the wire, not only do the detection limit and the sensitivity change, but also the resolution of the sensor can be effectively modulated. A mechanical model is proposed to explain the observed phenomenon. This prototype device guides the design of spatial force sensors with tunable performances, which may have great applications in smart M/NEMS, nanorobotics, high resolution touchscreens and even personal electronics.

A self-powered strain senor based on a ZnO/PEDOT:PSS hybrid structure

We report a self-powered strain sensor based on ZnO/PEDOT:PSS hybrid structure on a flexible polystyrene substrate. The electrical transport of the hybrid structure was modulated by the strain. The sensitivity of the fabricated device is enhanced to 1.0 × 104 under solar light, due to the piezo-phototronic effect of ZnO. The possible mechanism was discussed using energy band diagrams.

Electrically pumped lasing from single ZnO micro/nanowire and poly(3,4-ethylenedioxythiophene):poly(styrenexulfonate) hybrid heterostructures

We report electrically driven ultraviolet lasing by electrical injection in a single ZnO micro/nanowire. Heterojunctions were fabricated by contacting poly(3,4-ethylenedioxythiophene): poly(styrenexulfonate) (PEDOT:PSS) with one end of a single ZnO wire. At an excitation injection of ∼1 A/cm2, the electroluminescence spectrum showed a near-ultraviolet lasing action. This phenomenon was understood based on whispering-gallery mode, which results from trajectories that traverse a polygonal cross-section near the edges of the cylinder. The reduction of some modes was associated with the surface states or defects and the resonance below the intrinsic exciton emission of ZnO is related to electron accumulation at the polymer/ZnO interface.

Saturated blue-violet electroluminescence from single ZnO micro/nanowire and p-GaN film hybrid light-emitting diodes

Saturated electroluminescence behavior was observed in single ZnO micro/nanowire and GaN film heterojunctions fabricated by transferring an individual ZnO micro/nanowire onto p-type GaN substrate. A strong blue emission of ∼460 nm was observed, as a result of interfacial radiative recombination of electrons from n-ZnO and holes from p-GaN. Light-output-current characteristic followed a power law of L ∼ Im, which revealed a superlinear dependence at low current (m = 1.16) and became sublinear (m = 0.72) at high current. According to theoretical analysis, the saturated electroluminescence at high current could be attributed to the saturation of nonradiative recombination and the limitation of electrical-to-optical conversion efficiency.

Enhancing sensitivity of force sensor based on a ZnO tetrapod by piezo-phototronic effect

A force sensor based on a zinc oxide tetrapod is provided in this paper. The performance of the device was fully investigated by atomic force microscopy. Tuning Schottky barrier height by Piezo-phototronic effect leads to the increasing sensitivity of sensor from 0.17 A/N to 2.05 A/N under forward bias. The possible mechanisms have been proposed and discussed.

Size dependence and UV irradiation tuning of the surface potential in single conical ZnO nanowires

Investigating and tailoring surface potential changes of a system at the interfaces is of significance in the fundamental understanding and application of semiconductor devices. Thus the surface potential of zinc oxide (ZnO) nanowires is a vital factor to tune the performance of devices. In this paper, Kelvin probe force microscopy (KPFM) is used to measure the surface potential of single conical ZnO nanowires with different diameters. A size dependence of the surface potential in single conical ZnO nanowires is experimentally revealed. As the diameter decreases, the surface potential of the ZnO nanowires is found to decrease linearly under 400 nm. At large diameters (≥400 nm), the surface potential remains almost constant. The contact potential difference of the ZnO–PtIr tip increases to saturation after 40 min UV illumination and remains stable. An energy band theory is introduced to explore the surface potential change of ZnO nanowires under UV illumination. This study provides an understanding of the surface electrical properties of semiconductors at the nanoscale, which is valuable for optimizing functional nanodevices based on semiconductor nanowires.

An enzymatic biosensor based on three-dimensional ZnO nanotetrapods spatial net modified AlGaAs/GaAs high electron mobility transistors

We designed and constructed three dimensional (3D) zinc oxide Nanotetrapods (T-ZnOs) modified AlGaAs/GaAs high electron mobility transistors (HEMTs) for enzymatic uric acid (UA) detection. The chemical vapor deposition synthesized T-ZnOs was distributed on the gate areas of HEMTs in order to immobilize uricase and improve the sensitivity of the HEMTs. Combining with the high efficiency of enzyme immobilization by T-ZnOs and high sensitivity from HEMT, the as-constructed uricase/T-ZnOs/HEMTs biosensor showed fast response towards UA at ∼1 s, wide linear range from 0.2 nM to 0.2 mM and the low detect limit at 0.2 nM. The results point out an avenue to design electronic device as miniaturized lab-on-chip device for high sensitive and specific in biomedical and clinical diagnosis applications.

High-throughput fabrication of large-scale highly ordered ZnO nanorod arrays via three-beam interference lithography

Large-scale highly ordered ZnO nanorod arrays with precise period control and uniform distribution are easily fabricated via three-beam interference lithography, top anti-reflective coating and hydrothermal synthesis. This new method demonstrates an efficient way to fabricate large-scale highly ordered semiconductor nanorod arrays and could meet the needs of nanomaterial design, nanodevice optimization and nanosystem integration.