1wileyonlinelibrary.com schemes, the fl exible functional sensors are competitive and attractive candidates for promoting the advancement of sensing system. Recently, for the achievement of sensing devices, the printing technique has attracted widespread attention and been pursued to deposit various materials, like carbon materials, [ 13,23,24 ] polymers, [ 25,26 ] metals, [ 12,27 ] and semiconductors, [ 28,29 ] because the process is low energy consumption while maintaining the unique properties of the materials. By this way, the fl exible devices can be cheaper and easily produced.Graphite, one of carbon allotropes, has been increasing wide and keen interests of researchers, due to a wonder material of graphene. [ 9,[30][31][32] Pencil, a day-to-day material, is a nanocomposite of graphite and intercalated clay. [33][34][35] Being layered or pelleted, pencil lead can be exfoliated by using a gentle force. The drawing process can easily deposit graphite onto a rough paper, which contains massive amounts of cellulose fi bers and offer a naturally porous structure. [ 13,36 ] Pencil-trace drawn on printing papers is perhaps the simplest and easiest way of constructing graphite-based devices. The pen-on-paper (PoP) approach, a basic printing technique, offers a unique method to fabricate fl exible devices, such as strain sensors, [ 35 ] biosensors, [ 19,37 ] microfl uidic chips, [ 38 ] electronic devices, [ 34,39 ] photoconductive sensors, [ 29,40 ] and energy-storage devices. [ 33,41,42 ] Most of these devices have a response to force-induce changes in capacitance [ 33 ] and resistivity. [ 35 ] The microcontact-reversible sensing can effectively translate the microstructural deformations into electrical signals on active fl exible substrates. [ 6,9,43,44 ] As the potential to make fl exible, lightweight, portable, biocompatible, economical, and environment-friendly products, the PoP approach has an important role on the breakthroughs toward fl exible and wearable sensing devices.Herein, we demonstrate that the application of PoP approach can be expanded further to crucial fl exible sensing devices. We evaluated the repeatability of bending-unbending and the robustness of the strain sensors applied by loading. The strain sensors have a rapid respond to microdeformation changes and can be used to monitor various structural change and even human motion through facilitative and effective installing designs. Typically, the microdeformation of <0.13% strain can be detected. Compared with the recently reported fl exible sensing devices, the strain sensors behave signifi cant Flexible and Highly Sensitive Strain Sensors Fabricated by Pencil Drawn for Wearable MonitorXinqin Liao , Qingliang Liao , Xiaoqin Yan , Qijie Liang , Haonan Si , Minghua Li , Hualin Wu , Shiyao Cao , and Yue Zhang * Functional electrical devices have promising potentials in structural health monitoring system, human-friendly wearable interactive system, smart robotics, and even future multifunctional intelligent room. Here, a low-cost fabrication s...

Stretchable and multifunctional sensors can be applied in multifunctional sensing devices, safety forewarning equipment, and multiparametric sensing platforms. However, a stretchable and multifunctional sensor was hard to fabricate until now. Herein, a scalable and efficient fabrication strategy is adopted to yield a sensor consisting of ZnO nanowires and polyurethane fibers. The device integrates high stretchability (tolerable strain up to 150%) with three different sensing capabilities, i.e., strain, temperature, and UV. Typically achieved specifications for strain detection are a fast response time of 38 ms, a gauge factor of 15.2, and a high stability of >10 000 cyclic loading tests. Temperature is detected with a high temperature sensitivity of 39.3% °C−1, while UV monitoring features a large ON/OFF ratio of 158.2. With its fiber geometry, mechanical flexibility, and high stretchability, the sensor holds tremendous prospect for multiparametric sensing platforms, including wearable devices.

The well-defined silver (Ag) nanowires with five-twinned structure have been prepared by polyol reduction in the presence of poly(vinylpyrrolidone) (PVP K-30, 40 000). The obtained Ag nanowires are nearly monodispersed with an average diameter of 70 nm and length of 6 μm. It is confirmed from the results of thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Fourier transform Raman spectra (FT-Raman) that one monolayer of the PVP molecules might be absorbed on the surface of the Ag nanowires through Ag−O coordination. On the basis of the experimental analysis, the probable spatial conformation of the PVP molecules is supposed to be that the CH skeleton chain of the PVP is close to the surface of the Ag nanowires. The pyrrolidone ring might be tilted on the surface of the Ag nanowires through Ag:O coordination. These results may provide direct evidence for the role of the PVP molecules in the formation of the Ag nanowires.

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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.