Recently, the quest for new highly stretchable transparent tactile sensors with large-scale integration and rapid response time continues to be a great impetus to research efforts to expand the promising applications in human-machine interactions, artificial electronic skins, and smart wearable equipment. Here, a self-powered, highly stretchable, and transparent triboelectric tactile sensor with patterned Ag-nanofiber electrodes for detecting and spatially mapping trajectory profiles is reported. The Ag-nanofiber electrodes demonstrate high transparency (>70%), low sheet resistance (1.68-11.1 Ω □ ), excellent stretchability, and stability (>100% strain). Based on the electrode patterning and device design, an 8 × 8 triboelectric sensor matrix is fabricated, which works well under high strain owing to the effect of the electrostatic induction. Using cross-locating technology, the device can execute more rapid tactile mapping, with a response time of 70 ms. In addition, the object being detected can be made from any commonly used materials or can even be human hands, indicating that this device has widespread potential in tactile sensing and touchpad technology applications.

A pressure-sensor matrix (PSM) with full dynamic range can accurately detect and spatially map pressure profiles. A 100 × 100 large-scale PSM gives both electrical and optical signals by itself without applying an external power source. The device represents a major step toward digital imaging, and the visible display of the pressure distribution covers a large dynamic range.

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Two-dimensional (2D) materials, possessing numerous remarkable properties including high electrical conductivity, optical transparency and mechanical strength, have supplied a fertile soil for theoretical research and practical application in electronics and optoelectronics. Due to a persistent need of strain sensors, microelectromechnical system (MEMS), nanorobots and active flexible electronics, piezotronic and piezo-phototronic effect of 2D materials have been attracting growing attentions in latest years. Therefore, a comprehensive and intensive understanding of piezotronic and piezo-phototronic effect of 2D materials is required. Here we review the recent progress in theoretical analysis and experimental observation of piezotronic and piezo-phototronic effect of 2D materials enabled by non-centrosymmetric crystal structure. After introducing the fundamental physics of piezotronic and piezo-phototronic effect concisely, the origination and analysis of the piezoelectricity in 2D materials are discussed in detail. Furthermore, we focus on the application in piezotronic and piezo-phototronic effect of transition-metal dichalcogenides (TMDCs) including transistor, nanogenerator, humidity sensor and photodetector. Moreover, some other 2D piezoelectric materials (PEMs) are also been summarized owing to their potential applications in piezotronics and piezo-phtotronics. Finally, some perspectives are put forward on the following opportunities and challenges for future research in this emerging field.

We report a dynamic tuning on coherent light emission wavelengths of single ZnO microwire by using the piezoelectric effect. Owing to the dominant role occupied by the piezoelectric polarization effect in the wurtzite-structure ZnO microwire, the effective dielectric constant (or refraction index) of the gain media was modulated toward an increasing trend by applying a tensile strain, resulting in a shift of the strain-mediated whispering-gallery mode (WGM) lasing at room temperature. Also, the strain required to resolve the spectra in the two operating types of PL and lasing were systematically analyzed and compared. Because of the narrow line width in the lasing mode, the strain-dependent spectral resolution was improved by an order of magnitude, making it feasible for achieving high-precision, ultrasensitive, and noncontact stress sensing. Our results have an important impact on laser modulation, optical communication, and optical sensing technology.

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