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We demonstrated the first piezoelectric effect on the performance of a pH sensor using an MSM back-to-back Schottky contacted ZnO micro/nanowire device. When the device is subjected to an external strain, a piezopotential is created in the micro/nanowire, which tunes the effective heights of the Schottky barriers at the local contacts, consequently increasing the sensitivity and signal level of the sensors. Furthermore, the strain-produced piezopotential along the ZnO micro/nanowire will lead to a nonuniform distribution of the target molecules near the micro/nanowire surface owing to electrostatic interaction, which will make the sensor proactive to detect the target molecules even at extremely low overall concentration, which naturally improves the sensitivity and lowers the detection limit. A theoretical model is proposed to explain the observed performance of the sensor using the energy band diagram. This prototype device offers a new concept for designing supersensitive and fast-response micro/nanowire sensors by introducing an external strain and piezotronic effect, which may have great applications in building sensors with fast response and reset time, high selectivity, high sensitivity, and good signal-to-noise ratio for chemical, biochemical, and gas sensing.

The piezo-phototronic effect on transport properties of flexible CdSe NW devices is investigated. An optimum sensitivity of the flexible CdSe NW devices can be achieved by adjusting the applied strain and illumination intensity. The piezo-phototronic effect under compressive strain increases the internal electric field of the Schottky barrier, and assists the separation of the photo-excited electron-hole pairs, resulting in the increase of photocurrent. A trap-mediated mechanism is responsible for the decreased hole separation when the strain is larger than the critical strain., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The piezoelectric characteristics of nanowires, thin films and bulk crystals have been closely studied for potential applications in sensors, transducers, energy conversion and electronics. With their high crystallinity and ability to withstand enormous strain, two-dimensional materials are of great interest as high-performance piezoelectric materials. Monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. Here we report the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. The coupling between piezoelectricity and semiconducting properties in two-dimensional nanomaterials may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics. [ABSTRACT FROM AUTHOR]

Nanowire solar cells are promising candidates for poweringnanosystemsand flexible electronics. The strain in the nanowires, introducedduring growth, device fabrication and/or application, is an importantissue for piezoelectric semiconductor (like CdS, ZnO, and CdTe) basedphotovoltaic. In this work, we demonstrate the first largely enhancedperformance of n-CdS/p-Cu2S coaxial nanowire photovoltaic(PV) devices using the piezo-phototronics effect when the PV deviceis subjected to an external strain. Piezo-phototronics effect couldcontrol the electron–hole pair generation, transport, separation,and/or recombination, thus enhanced the performance of the PV devicesby as high as 70%. This effect offers a new concept for improvingsolar energy conversation efficiency by designing the orientationof the nanowires and the strain to be purposely introduced in thepackaging of the solar cells. This study shed light on the enhancedflexible solar cells for applications in self-powered technology,environmental monitoring, and even defensive technology. [ABSTRACT FROM AUTHOR]

A comprehensiveinvestigation was carried out on n-type ZnO nanowiresfor studying the temperature dependence of the piezotronic effectfrom 77 to 300 K. In general, lowering the temperature results ina largely enhanced piezotronic effect. The experimental results showthat the behaviors can be divided into three groups depending on thecarrier doping level or conductivity of the ZnO nanowires. For nanowireswith a low carrier density (<1017/cm3at77 K), the pieozotronic effect is dominant at low temperature fordictating the transport properties of the nanowires; an opposite changeof Schottky barrier heights at the two contacts as a function of temperatureat a fixed strain was observed for the first time. At a moderate doping(between 1017/cm3and 1018/cm3at 77 K), the piezotronic effect is only dominant at onecontact, because the screening effect of the carriers to the positivepiezoelectric polarization charges at the other end (for n-type semiconductors).For nanowires with a high density of carriers (>1018/cm3at 77 K), the piezotronic effect almost vanishes.This studynot only proves the proposed fundamental mechanism of piezotroniceffect, but also provides guidance for fabricating piezotronic devices. [ABSTRACT FROM AUTHOR]