Ruomeng Yu

Triboelectric-Generator-Driven Pulse Electrodeposition for Micropatterning

By converting ambient energy into electricity, energy harvesting is capable of at least offsetting, or even replacing, the reliance of small portable electronics on traditional power supplies, such as batteries. Here we demonstrate a novel and simple generator with extremely low cost for efficiently harvesting mechanical energy that is typically present in the form of vibrations and random displacements/deformation. Owing to the coupling of contact charging and electrostatic induction, electric generation was achieved with a cycled process of contact and separation between two polymer films. A detailed theory is developed for understanding the proposed mechanism. The instantaneous electric power density reached as high as 31.2 mW/cm(3) at a maximum open circuit voltage of 110 V. Furthermore, the generator was successfully used without electric storage as a direct power source for pulse electrodeposition (PED) of micro/nanocrystalline silver structure. The cathodic current efficiency reached up to 86.6%. Not only does this work present a new type of generator that is featured by simple fabrication, large electric output, excellent robustness, and extremely low cost, but also extends the application of energy-harvesting technology to the field of electrochemistry with further utilizations including, but not limited to, pollutant degradation, corrosion protection, and water splitting.

Recent Progress in Electronic Skin.

The skin is the largest organ of the human body and can sense pressure, temperature, and other complex environmental stimuli or conditions. The mimicry of human skins sensory ability via electronics is a topic of innovative research that could find broad applications in robotics, artificial intelligence, and human–machine interfaces, all of which promote the development of electronic skin (e‐skin). To imitate tactile sensing via e‐skins, flexible and stretchable pressure sensor arrays are constructed based on different transduction mechanisms and structural designs. These arrays can map pressure with high resolution and rapid response beyond that of human perception. Multi‐modal force sensing, temperature, and humidity detection, as well as self‐healing abilities are also exploited for multi‐functional e‐skins. Other recent progress in this field includes the integration with high‐density flexible circuits for signal processing, the combination with wireless technology for convenient sensing and energy/data transfer, and the development of self‐powered e‐skins. Future opportunities lie in the fabrication of highly intelligent e‐skins that can sense and respond to variations in the external environment. The rapidly increasing innovations in this area will be important to the scientific community and to the future of human life.

Dynamic Pressure Mapping of Personalized Handwriting by a Flexible Sensor Matrix Based on the Mechanoluminescence Process

A self-powered pressure-sensor matrix based on ZnS:Mn particles for more-secure signature collection is presented, by recording both handwritten signatures and the pressure applied by the signees. This large-area, flexible sensor matrix can map 2D pressure distributions in situ, either statically or dynamically, and the piezophotonic effect is proposed to initiate the mechanoluminescence process once a dynamic mechanical strain is applied.

Enhanced Cu2S/CdS Coaxial Nanowire Solar Cells by Piezo-Phototronic Effect

Nanowire solar cells are promising candidates for powering nanosystems and flexible electronics. The strain in the nanowires, introduced during growth, device fabrication and/or application, is an important issue for piezoelectric semiconductor (like CdS, ZnO, and CdTe) based photovoltaic. In this work, we demonstrate the first largely enhanced performance of n-CdS/p-Cu(2)S coaxial nanowire photovoltaic (PV) devices using the piezo-phototronics effect when the PV device is subjected to an external strain. Piezo-phototronics effect could control the electron-hole pair generation, transport, separation, and/or recombination, thus enhanced the performance of the PV devices by as high as 70%. This effect offers a new concept for improving solar energy conversation efficiency by designing the orientation of the nanowires and the strain to be purposely introduced in the packaging of the solar cells. This study shed light on the enhanced flexible solar cells for applications in self-powered technology, environmental monitoring, and even defensive technology.

Piezotronic Effect on the Transport Properties of GaN Nanobelts for Active Flexible Electronics

The transport properties of GaN nanobelts (NBs) are tuned using a piezotronic effect when a compressive/tensile strain is applied on the GaN NB. This is mainly due to a change in Schottky barrier height (SBH). A theoretical model is proposed to explain the observed phenomenon.

High performance of ZnO nanowire protein sensors enhanced by the piezotronic effect

Based on a metal–semiconductor–metal structure, the performance of a ZnO nanowire (NW) based sensor has been studied for detecting Immunoglobulin G (IgG)-targeted protein. By applying a compressive strain, the piezotronic effect on ZnO NW protein sensors can not only increase the resolution of such sensors by tens of times, but also largely improve the detection limit and sensitivity. A theoretical model is proposed to explain the observed behaviors of the sensor. This study demonstrates a prospective approach to raise the resolution, improve the detection limit and enhance the general performance of a biosensor.

Piezotronic Effect on the Sensitivity and Signal Level of Schottky Contacted Proactive Micro/Nanowire Nanosensors

We demonstrated the first piezoelectric effect on the performance of a pH sensor using an MSM back-to-back Schottky contacted ZnO micro/nanowire device. When the device is subjected to an external strain, a piezopotential is created in the micro/nanowire, which tunes the effective heights of the Schottky barriers at the local contacts, consequently increasing the sensitivity and signal level of the sensors. Furthermore, the strain-produced piezopotential along the ZnO micro/nanowire will lead to a nonuniform distribution of the target molecules near the micro/nanowire surface owing to electrostatic interaction, which will make the sensor proactive to detect the target molecules even at extremely low overall concentration, which naturally improves the sensitivity and lowers the detection limit. A theoretical model is proposed to explain the observed performance of the sensor using the energy band diagram. This prototype device offers a new concept for designing supersensitive and fast-response micro/nanowire sensors by introducing an external strain and piezotronic effect, which may have great applications in building sensors with fast response and reset time, high selectivity, high sensitivity, and good signal-to-noise ratio for chemical, biochemical, and gas sensing.

Electret film-enhanced triboelectric nanogenerator matrix for self-powered instantaneous tactile imaging.

We report the first self-powered electronic skin that consists of light-emitting diode (LED) and triboelectric nanogenerator (TENG) arrays that can be utilized for spatially mapping applied instantaneous-touch events and tracking the movement location of the target object by recording the electroluminescent signals of the LEDs without external power sources. The electret film-based TENG can deliver an open-circuit voltage of about -1070 V, a short-circuit current density of 10 mA/m(2), and a power density of 288 mW/m(2) on an external load of 100 MΩ. The LEDs can be turned on locally when the back surface of the active matrix is touched, and the intensity of the emitted light depends on the magnitude of the applied local pressure on the device. A constructed active matrix of the LED-TENG array (8 × 7 pixels) can achieve self-powered, visual, and high-resolution tactile sensing by recording the electroluminescent signals from all of the pixels, where the active size of each pixel can be decreased to 10 mm(2). This work is a significant step forward in self-powered tactile-mapping visualization technology, with a wide range of potential applications in touchpad technology, personal signatures, smart wallpapers, robotics, and safety-monitoring devices.

Optimizing performance of silicon-based p-n junction photodetectors by the piezo-phototronic effect.

Silicon-based p-n junction photodetectors (PDs) play an essential role in optoelectronic applications for photosensing due to their outstanding compatibility with well-developed integrated circuit technology. The piezo-phototronic effect, a three-way coupling effect among semiconductor properties, piezoelectric polarizations, and photon excitation, has been demonstrated as an effective approach to tune/modulate the generation, separation, and recombination of photogenerated electron-hole pairs during optoelectronic processes in piezoelectric-semiconductor materials. Here, we utilize the strain-induced piezo-polarization charges in a piezoelectric n-ZnO layer to modulate the optoelectronic process initiated in a p-Si layer and thus optimize the performances of p-Si/ZnO NWs hybridized photodetectors for visible sensing via tuning the transport property of charge carriers across the Si/ZnO heterojunction interface. The maximum photoresponsivity R of 7.1 A/W and fastest rising time of 101 ms were obtained from these PDs when applying an external compressive strain of -0.10‰ on the ZnO NWs, corresponding to relative enhancement of 177% in R and shortening to 87% in response time, respectively. These results indicate a promising method to enhance/optimize the performances of non-piezoelectric semiconductor material (e.g., Si) based optoelectronic devices by the piezo-phototronic effect.

Light-induced pyroelectric effect as an effective approach for ultrafast ultraviolet nanosensing

Zinc oxide is potentially a useful material for ultraviolet detectors; however, a relatively long response time hinders practical implementation. Here by designing and fabricating a self-powered ZnO/perovskite-heterostructured ultraviolet photodetector, the pyroelectric effect, induced in wurtzite ZnO nanowires on ultraviolet illumination, has been utilized as an effective approach for high-performance photon sensing. The response time is improved from 5.4 s to 53 μs at the rising edge, and 8.9 s to 63 μs at the falling edge, with an enhancement of five orders in magnitudes. The specific detectivity and the responsivity are both enhanced by 322%. This work provides a novel design to achieve ultrafast ultraviolet sensing at room temperature via light-self-induced pyroelectric effect. The newly designed ultrafast self-powered ultraviolet nanosensors may find promising applications in ultrafast optics, nonlinear optics, optothermal detections, computational memories and biocompatible optoelectronic probes.