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Flexible sensors have attracted increasing research interest due to their broad application potential in the fields of human-computer interaction, medical care, sports monitoring, etc. Constructing an integrated sensor system with high performance and being capable of discriminating different stimuli remains a challenge. Here, we proposed a flexible integrated sensor system for motion monitoring that can measure bending strain and pressure independently with a low-cost and simple fabrication process. The resistive bending strain sensor in the system is fabricated by sintering polyimide (PI), demonstrating a gauge factor of 9.54 and good mechanical stability, while the resistive pressure sensor is constructed based on a composite structure of silver nanowires (AgNWs) and polydimethylsiloxane (PDMS)-expandable microspheres with a tunable sensitivity and working range. Action recognition is demonstrated by attaching the flexible integrated sensor system on the wrist with independent strain and pressure information recorded from corresponding sensors. It shows a great application potential in motion monitoring and intelligent human-machine interfaces.

A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.

The piezophototronic effect is known as a three-way coupling between piezoelectric polarization, semiconductor property, and optical excitation in piezoelectric semiconductor materials to modify their energy band structures by strain-induced piezoelectric polarization charges, and thus to tune/control their optoelectronic processes of charge carrier generation, separation, recombination, and transport. In this work, the temperature dependence of the piezophototronic effect in wurtzite-structured CdS nanowires is investigated from 77 to 300 K. The piezophototronic effect is enhanced by over 550% under lower temperature due to the increased effective piezoelectric polarization surface/interface charges resulting from the reduced screening effect by decreased mobile charge carriers in CdS nanowires. Optoelectronic performances of CdS nanowires are systematically investigated under various light illuminations, strains, and temperatures. By analyzing the corresponding band diagrams, the piezophototronic effect is found to dominate the transport and separation processes of charge carriers. This study presents in-depth fundamental understanding about the piezophototronic effect and provides guidance for its future applications in optoelectronic devices. [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]

Abstract: In this paper, we fabricated transparent flexible nanogenerators (NGs) by employing flexible polydimethylsiloxane (PDMS) substrate for the growth of ZnO nanowires. The fully packaged NG showed good transparency with a transmittance of 50–60% in the visible range. The output voltage and current was 8V and 0.6μA, respectively, corresponding to an output power density of ∼5.3mW/cm3. The NG also showed excellent robustness and could stably scavenge energy from the motion of a vehicle. Based on this characteristic, we demonstrated its application as a self-powered sensor for monitoring vehicle speed and detecting vehicle weight. [Copyright &y& Elsevier]

Abstract: Relying on the piezopotential created in ZnO under straining, nanogenerators, piezotronics and piezo-phototronics developed based on laterally bonded nanowires on a polymer substrate have been reviewed. The principle of the nanogenerator is a transient flow of electrons in external load as driven by the piezopotential created by dynamic straining. By integrating the contribution made by millions of nanowires, the output voltage has been raised to 1.2V. Consequently, self-powered nanodevices have been demonstrated. This is an important platform technology for the future sensor network and the internet of things. Alternatively, the piezopotential can act as a gate voltage that can tune/gate the transport process of the charge carriers in the nanowire, which is a gate-electrode free field effect transistor (FET). The device fabricated based on this principle is called the piezotronic device. Piezo-phototronic effect is about the tuning and controlling of electro-optical processes by strain induced piezopotential. The piezotronic, piezophotonic and pieozo-phototronic devices are focused on low frequency applications in areas involving mechanical actions, such as MEMS/NEMS, nanorobotics, sensors, actuators and triggers. [ABSTRACT FROM AUTHOR]