Publications

Flexible tactile sensors show promise for artificial intelligence applications due to their biological adaptability and rapid signal perception. Triboelectric sensors enable active dynamic tactile sensing, while integrating static pressure sensing and real-time multichannel signal transmission is key for further development. Here, we propose an integrated structure combining a capacitive sensor for static spatiotemporal mapping and a triboelectric sensor for dynamic tactile recognition. A liquid metal-based flexible dual-mode triboelectric-capacitive-coupled tactile sensor (TCTS) array of 4 × 4 pixels achieves a spatial resolution of 7 mm, exhibiting a pressure detection limit of 0.8 Pa and a fast response of 6 ms. Furthermore, neuromorphic computing using the MXene-based synaptic transistor achieves 100% recognition accuracy of handwritten numbers/letters within 90 epochs based on dynamic triboelectric signals collected by the TCTS array, and cross-spatial information communication from the perceived multichannel tactile data is realized in the mixed reality space. The results illuminate considerable application possibilities of dual-mode tactile sensing technology in human-machine interfaces and advanced robotics.

Using a two-step seed-mediated growth method, we synthesized bimetallic nanoparticles (NPs) having a gold octahedron core and a palladium epitaxial shell with controlled Pd-shell thickness. The mismatch-release mechanism between the Au core and Pd shell of the NPs was systematically investigated by high-resolution transmission electron microscopy. In the NPs coated with a single atomic layer of Pd, the strain between the surface Pd layer and the Au core is released by Shockley partial dislocations (SPDs) accompanied by the formation of stacking faults. For NPs coated with more Pd (>2 nm), the stacking faults still exist, but no SPDs are found. This may be due to the diffusion of Au atoms into the Pd shell layers to eliminate the SPDs. At the same time, a long-range ordered L11 AuPd alloy phase has been identified in the interface area, supporting the assumption of the diffusion of Au into Pd to release the interface mismatch. With increasing numbers of Pd shell layers, the shape of the Au−Pd NP changes, step by step, from truncated-octahedral to cubic. After the bimetallic NPs were annealed at 523 K for 10 min, the SPDs at the surface of the NPs coated with a single atomic layer of Pd disappeared due to diffusion of the Au atoms into the surface layer, while the stacking faults and the L11 Au−Pd alloyed structure remained. When the annealing temperature was increased to 800 K, electron diffraction patterns and diffraction contrast images revealed that the NPs became a uniform Au−Pd alloy, and most of the stacking faults disappeared as a result of the annealing. Even so, some clues still support the existence of the L11 phase, which suggests that the L11 phase is a stable, long-range ordered structure in Au−Pd bimetallic NPs.

Abstract This study reports a self‐powered pressure sensor based on a monocharged electret nanogenerator (MENG). The sensor exhibits great advantages in terms of high reliability, ease of fabrication, and relatively high sensitivity. The working mechanism of the MENG sensor is studied by both theoretical derivations and finite element analyses to determine the electric potential distribution during the device operation. The MENG sensor exhibits a stable open circuit voltage ≈10 V at a 30.8 kPa pressure and a corresponding sensitivity of 325 mV kPa −1 . The stability testing result shows that the device has only ≈5% attenuation after 10 000 cycles of repeated testing at 30.8 kPa pressure. Furthermore, it is found that the MENG sensor responds not only to a dynamic force but also a static force. Finally, a sensor array consisting of nine MENG sensor elements is fabricated. The testing results from the sensor array also reveal that a single touch of the sensor element can immediately light up an LED light at the corresponding position. This device holds great promise for use in future tactile sensors and artificial skin applications.

The piezotronic effect uses strain-induced piezoelectric charges at interfaces and junctions to tune and/or control carrier transport in piezoelectric semiconductor devices. This effect has recently been observed in single-layer 2D MoS2 materials. However, previous work had found that metallic states are generated at the edge of a free-standing MoS2 flat sheet, and these states may screen the piezoelectric charges. Using density functional theory simulations, we found that the metal–MoS2 interface structure plays an important role in enhancing both the piezoelectric and piezotronic effects in MoS2 transistors by breaking the metallic state screening effect at the MoS2 edge. This study not only provides an understanding of the piezoelectric and piezotronic effects based on first principles calculations but also offers guidance for the design of two-dimensional piezotronic devices.

Abstract As a coupling effect of pyroelectric and photoelectric effect, pyro‐phototronic effect has demonstrated an excellent tuning role for fast response p–n junction photodetectors (PDs). Here, a comprehensive pyro‐phototronic effect is utilized to design and fabricate a self‐powered and flexible ultraviolet PD based on the ZnO/Ag Schottky junction. By using the primary pyroelectric effect, the maximal transient photoresponsivity of the self‐powered PDs can reach up to 1.25 mA W −1 for 325 nm illumination, which is improved by 1465% relative to that obtained from the steady‐state signal. The relative persistent secondary pyroelectric effect weakens the height of Schottky barrier, leading to a reduction of the steady‐state photocurrent with an increase in the power density. When the power density is large enough, the steady‐state photocurrent turns into a reverse direction. The corresponding tuning mechanisms of the comprehensive pyro‐phototronic effect on transient and steady‐state photocurrent are revealed based on the bandgap diagrams. The results may help us to further clarify the mechanism of the pyro‐phototronic effect on the photocurrent and also provide a potential way to optimize the performance of self‐powered PDs.

The equilibrium piezoelectric potential distribution in a deformed ZnO semiconductive nanowire has been systematically investigated in order to reveal its dependence on the donor concentration, applied force, and geometric parameters. In particular, the donor concentration markedly affects the magnitude and distribution of the electric potential. At a donor concentration of N D>1018 cm−3, the piezopotential is almost entirely screened. Among the other parameters, a variation in the length of the nanowire does not significantly affect the potential distribution.

Tin dioxide is the most used material for gas sensing because its three-dimensional nanostructures and properties are related to the large surface exposed to gas adsorption. We propose the use of a two-dimensional nanostructure of SnO2 in the form of nanobelts; such newly achieved layers have been found to exhibit electrical properties that are similar to their three-dimensional counterpart but with the unique feature of being a pure crystal. Such a characteristic would guarantee long-term stability for the nanobelts, a condition which is not always met with three-dimensional nanostructures because of the occurrence of grain coalescence. In this framework, we developed an analytical approach to model the electrical properties of one-, two-, or three-dimensional nanostructures.

By combining contact-mode atomic force microscopy (AFM) and scanning Kevin probe microscopy (SKPM), we demonstrated an in situ method for quantitative characterization of the triboelectrification process at the nanoscale. We systematically characterized the triboelectric charge distribution, multifriction effect on charge transfer, as well as subsequent charge diffusion on the dielectric surface: (i) the SiO2 surface can be either positively or negatively charged through triboelectric process using Si-based AFM probes with and without Pt coating, respectively; (ii) the triboelectric charges accumulated from multifriction and eventually reached to saturated concentrations of (-150 ± 8) μC/m(2) and (105 ± 6) μC/m(2), respectively; (iii) the charge diffusion coefficients on SiO2 surface were measured to be (1.10 ± 0.03) × 10(-15) m(2)/s for the positive charge and (0.19 ± 0.01) × 10(-15) m(2)/s for the negative charges. These quantifications will facilitate a fundamental understanding about the triboelectric and de-electrification process, which is important for designing high performance triboelectric nanogenerators. In addition, we demonstrated a technique for nanopatterning of surface charges without assistance of external electric field, which has a promising potential application for directed self-assembly of charged nanostructures for nanoelectronic devices.

We demonstrate the first electric field induced transverse deflection of a single-crystal, free-standing ZnO microbelt as a result of converse piezoelectric effect. For a microbelt growing along the c-axis, a shear stress in the a-c plane can be induced when an electric field E is applied along the a-axis of the wurtzite structure. As amplified by the large aspect ratio of the microbelt that grows along the c-axis, the strain localized near the root can be detected via the transverse deflection perpendicular to the ZnO microbelt. After an experimental approach was carefully designed and possible artifacts were ruled out, the experimentally observed degree of deflection of the microbelt agrees well with the theoretically expected result. The device demonstrated has potential applications as transverse actuators/sensors/switches and electric field induced mechanical deflectors.

Abstract The development of wearable electronics and sensing networks has increased the demand for wearable power modules that have steady output, high energy density, and long cycle life. Current power modules, such as batteries, suffer from low energy density due to their limited storage capacity. One solution to avoid the issue is to build a hybrid device consisting of both energy harvesting elements that continuously harvest ambient mechanical energy, and electrochemical energy storage units to store the harvested energy. Here, a hybrid energy harvesting bracelet, which combines a dual electromagnetic and triboelectric nanogenerator to harvest wrist motions, is reported. The bracelet is able to charge the RuO 2 ‐based microsupercapacitor to 2 V with a single shake of human wrist, which allows the supercapacitor to power most electronic devices for minutes, such as a calculator, relative humidity, and temperature sensors.

Abstract Recently, piezoelectric characteristics have been a research focus for 2D materials because of their broad potential applications. Black phosphorus (BP) is a monoelemental 2D material predicted to be piezoelectric because of its highly directional properties and non‐centrosymmetric lattice structure. However, piezoelectricity is hardly reported in monoelemental materials owing to their lack of ionic polarization, but piezoelectric generation is consistent with the non‐centrosymmetric structure of BP. Theoretical calculations of phosphorene have explained the origin of piezoelectric polarization among P atoms. However, the disappearance of piezoelectricity in multilayer 2D material generally arises from the opposite orientations of adjacent atomic layers, whereas this effect is limited in BP lattices due to their spring‐shaped space structure. Here, the existence of in‐plane piezoelectricity is experimentally reported for multilayer BP along the armchair direction. Current–voltage measurements demonstrate a piezotronic effect in this orientation, and cyclic compression and release of BP flakes show an intrinsic current output as large as 4 pA under a compressive strain of −0.72%. The discovery of piezoelectricity in multilayer BP can lead to further understanding of this mechanism in monoelemental materials.