Publications

The piezo-phototronic effect on transport properties of flexible CdSe NW devices is investigated. An optimum sensitivity of the flexible CdSe NW devices can be achieved by adjusting the applied strain and illumination intensity. The piezo-phototronic effect under compressive strain increases the internal electric field of the Schottky barrier, and assists the separation of the photo-excited electron-hole pairs, resulting in the increase of photocurrent. A trap-mediated mechanism is responsible for the decreased hole separation when the strain is larger than the critical strain.

A highly efficient TENG is achieved based on a charge reversion process arising from the electrostatic breakdown effect, which is supported by a modified dielectric capacitance model in theory, to improve the output performance.

A spherical TENG with a spring-assisted multilayered structure was power-managed to effectively harvest multidirectional water wave energy.

Abstract Electronic skin (e‐skin) has been under the spotlight due to great potential for applications in robotics, human–machine interfaces, and healthcare. Meanwhile, triboelectric nanogenerators (TENGs) have been emerging as an effective approach to realize self‐powered e‐skin sensors. In this work, bioinspired TENGs as self‐powered e‐skin sensors are developed and their applications for robotic tactile sensing are also demonstrated. Through the facile replication of the surface morphology of natural plants, the interlocking microstructures are generated on tribo‐layers to enhance triboelectric effects. Along with the adoption of polytetrafluoroethylene (PTFE) tinny burrs on the microstructured tribo‐surface, the sensitivity for pressure measurement is boosted with a 14‐fold increase. The tactile sensing capability of the TENG e‐skin sensors are demonstrated through the characterizations of handshaking pressure and bending angles of each finger of a bionic hand during handshaking with human. The TENG e‐skin sensors can also be utilized for tactile object recognition to measure surface roughness and discern hardness. The facile fabrication scheme of the self‐powered TENG e‐skin sensors enables their great potential for applications in robotic dexterous manipulation, prosthetics, human–machine interfaces, etc.

Strain-gated flexible optoelectronics are reported based on monolayer MoS2 . Utilizing the piezoelectric polarization created at the metal-MoS2 interface to modulate the separation/transport of photogenerated carriers, the piezophototronic effect is applied to implement atomic-layer-thick phototransistor. Coupling between piezoelectricity and photogenerated carriers may enable the development of novel optoelectronics.

Converting mechanical energy into direct-current electric power based on the tribovoltaic effect is a typical characteristic of tribovoltaic nanogenerators (TVNGs). Although this newly discovered physics effect has been devoted to numerous research studies recently, a generalized theoretical model is still missing, thus unable to comprehensively elaborate the working principles of TVNG. Unlike previous qualitative explanations restricted to the conventional diffusion-drift theory, a new theoretical model is proposed according to classical semiconductor physics. Using the model, the governing equation of a TVNG is derived for the first time, which provides possibilities for revealing the variations of basic physical variables whether within the device or in an external circuit. The direct-current output is suggested to be the coupling of the tribovoltaic effect and contact electrification; in detail, it directly results from the movement and realignment of quasi-Fermi levels for excess carriers that are contiguous to the junction/contacting interface under non-equilibrium conditions. Moreover, an equivalent circuit model is established, equivalent to a constant current source parallel to a p–n junction diode according to the lumped parameter circuit theory. Notably, a new term, mechano-induced electric field EM, is defined and introduced to describe the impact of triboelectric charges at interfaces. Furthermore, using the COMSOL Multiphysics software, a dynamic simulation model for TVNGs is proposed, allowing the simulation and calculation of various TVNGs with different geometric constructions and charge distributions.

Abstract Magnesium as a promising alloy‐type anode material for lithium‐ion batteries features both high theoretical specific capacity (2150 mAh g −1 ) and stack energy density (1032 Wh L −1 ). However, the poor cycling performance of Mg‐based anodes severely limits their application, mainly because high‐impedance films can grow easily on the surface of Mg and cause diminished electrochemical activity. As a result, the capacities of reported Mg anodes fade quickly in less than 100 cycles. To improve the stability of Mg anodes, 3D Cu@Mg@C structures are prepared by depositing Mg/C composite on 3D Cu current collectors. The resulting 3D Cu@Mg@C anodes can deliver an initial capacity of 1392 mAh g −1 . With a second‐cycle capacity of 1255 mAh g −1 , 91% can be retained after 1000 cycles at 0.5 C. When cycled at 2 C, the initial capacity can be maintained for 4000 cycles. This remarkably improved cycling performance can be attributed to both the 3D structure and the embedded carbon layers of the 3D Cu@Mg@C electrodes that facilitate electrical contact and prevent the growth of high‐impedance films during cycling. With 3D Cu@Mg@C anodes and LiFePO 4 cathodes, full cells are assembled and charging by a rotating triboelectric nanogenerator that can harvest mechanical energy is demonstrated.

There is an increasing demand for portable, reliable, and cost effective bioelectronic systems for applications ranging from clinical diagnosis to homeland security. Conventional detection systems involve labeling the probe molecules, large amount of target molecules to enable detection, and elaborate signal transduction methods. Most of them also have to couple with optical detection equipments that are bulky and expensive. One dimensional (1-D) and two dimensional (2-D) structures such as nanowire, nanobelts and films are capable of detecting the molecular interactions in terms of significant change in their electrical properties leading to ultrahigh sensitivity and easy integration. In this paper, we demonstrate ZnO nanowires based bio-sesnors to detect IgG antibodies. Current-voltage (I-V) and Scanning Electron Microscopy (SEM) characterization were used to monitor the change in the conductivity as well as morphology. By comparing with the reference sample, the specific binding event between anti-IgG and IgG antibodies was detected. The data indicated a conductivity change by more than 12% after the protein hybridization. SEM images confirm the morphological change from reference samples to reacted samples. In addition, same experiment protocols are carried out for ZnO thin film devices. Similar change in I-V characteristics and morphologies are observed. Through this work, we have demonstrated to use ZnO nanowires as building blocks to fabricate bio-sensors which can potentially detect any protein. Conductimetric sensing results in a label-free detection system as it detects the protein hybridization events electrically. It is a cost effective process, which can be exploited further by expanding into arrays and integrating with microfluidics. When integrated on the SOP platform, this technology can lead to portable, reliable and cost effective biosensors with applications in many areas.