High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices.

ZnO nanomaterials with their unique semiconducting and piezoelectric coupled properties have become promising materials for applications in piezotronic devices including nanogenerators, piezoelectric field effect transistors, and diodes. This article will mainly introduce the research progress on piezotronic properties of ZnO nanomaterials investigated by scanning probe microscopy (SPM) and ZnO-based prototype piezotronic nanodevices built in virtue of SPM, including piezoelectric field effect transistors, piezoelectric diodes, and strain sensors. Additionally, nanodamage and nanofailure of ZnO materials and their relevant piezotronic nanodevices will be critically discussed in their safe service in future nanoelectromechanical system (NEMS) engineering.

Well-aligned ZnO nanowires were synthesized by simple physical vapor deposition using c-oriented ZnO thin films as substrates without catalysts or additives. The synthesized ZnO nanowires have two typical average diameters: 60nm in majority and 120nm in minority. They are about 4μm in length and well aligned along the normal direction of the substrate. Most of the synthesized ZnO nanowires are single crystalline in a hexagonal structure and grow along the [001] direction. The c-oriented ZnO thin films control the growth direction. Photoluminescence spectrum was measured showing a single strong ultraviolet emission (380nm). Such result indicates that the ZnO nanowire arrays can be applied to excellent optoelectronic devices.

Strain sensors with high sensitivity, broad sensing ranges and excellent durable stability are highly desirable due to their promising potential in electronic skins and human-friendly wearable interactive systems. Herein, we report a high-performance strain sensor based on rGO (reduced graphene oxide)/DI (deionized water) sensing elements. The strain sensors were fabricated by using Ecoflex rubber filled with rGO/DI conductive liquids via template methods, making the process simple, low-cost and scalable. The as-assembled strain sensors can be used to reflect both stretching and compressing with high sensitivity (a maximum gauge factor of 31.6 and a pressure sensitivity of 0.122 kPa), an ultralow limit of detection (0.1% strain), and excellent reliability and stability (>15 000 cycles for pressuring and >10 000 cycles for stretching). In particular, the maximum sensing range is up to 400%, much wider than that of the sensor recently reported. More significantly, the strain sensors are able to distinguish between touch/compressive (resistance decrease) and tensile (resistance increase) deformation, which has not been explored before. This interesting property of strain sensors is due to the micro-contact of nanomaterials in a liquid environment. The sensing liquid of the device can be refilled when it fails, and this enables the recycling of the materials and reduces the waste rate. Therefore, it is attractive and promising for practical applications in multifunctional wearable electronics such as the detection of acoustic vibration, human vocalization and other human motions.

We report a self-powered ultraviolet photodetector based on a single Sb-doped ZnO nanobelt bridging an Ohmic contact and a Schottky contact. The photoresponse sensitivity and the response time of the fabricated device are as high as 2200% and less than 100 ms, respectively. The performance of the device dramatically degrades as the Sb-doping concentration decreases in the ZnO nanobelt. The possible mechanisms have been proposed and discussed.

Here, it is first reported that a self‐powered photodetector based on a MoS2/CH3NH3PbI3 vertical type heterojunction, which has responsivity of 60 mAW−1 and response/recovery time of 2149/899 ms. Under bias, it exhibits a photoswitching ratio exceeding 1522, fast response/recovery time of 205/206 ms, and high photoresponsivity of 68.11 AW−1. The optoelectronic performances of the photodetector are closely related to the type of the MoS2/CH3NH3PbI3 heterojunction, which acts as a hole (electron) transport field and can effectively decrease the recombination of holes and electrons. Additionally, the MoS2/CH3NH3PbI3 planar type heterojunction is also built to compare with the vertical type in optoelectronics behavior. Due to the existence of internal field, the properties of vertical type photodetector are better than those of the planar type which also presents good performance with on/off ratio up to 1476, photoresponsivity of 28 AW−1, and response rate of 356/204 ms. These results pave a new way to form an ultrahigh performance MoS2/CH3NH3PbI3 heterojunction, hold the promise for construction of a self‐powered photodetector, and develop promising atomically thin MoS2 heterostructure device for photovoltaic and optoelectronic applications.

Here surface potential of chemical vapor deposition (CVD) grown 2D MoS with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS are investigated. The surface potential of MoS on Si/SiO substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO , Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS , with the increase in light intensity, the surface potential of MoS on Si/SiO substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I-V curves on vertical of monolayer MoS /Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS /Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field.

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.