Wenzhuo Wu

Transparent Triboelectric Nanogenerators and Self-Powered Pressure Sensors Based on Micropatterned Plastic Films

Transparent, flexible and high efficient power sources are important components of organic electronic and optoelectronic devices. In this work, based on the principle of the previously demonstrated triboelectric generator, we demonstrate a new high-output, flexible and transparent nanogenerator by using transparent polymer materials. We have fabricated three types of regular and uniform polymer patterned arrays (line, cube, and pyramid) to improve the efficiency of the nanogenerator. The power generation of the pyramid-featured device far surpassed that exhibited by the unstructured films and gave an output voltage of up to 18 V at a current density of ∼0.13 μA/cm(2). Furthermore, the as-prepared nanogenerator can be applied as a self-powered pressure sensor for sensing a water droplet (8 mg, ∼3.6 Pa in contact pressure) and a falling feather (20 mg, ∼0.4 Pa in contact pressure) with a low-end detection limit of ∼13 mPa.

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO2 is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO2 core-shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm(2) and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm(2) and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems.

Nanotechnology-enabled energy harvesting for self-powered micro-/nanosystems.

Health, infrastructure, and environmental monitoring as well as networking and defense technologies are only some of the potential areas of application of micro-/nanosystems (MNSs). It is highly desirable that these MNSs operate without an external electricity source and instead draw the energy they require from the environment in which they are used. This Review covers various approaches for energy harvesting to meet the future demand for self-powered MNSs.

Taxel-Addressable Matrix of Vertical-Nanowire Piezotronic Transistors for Active and Adaptive Tactile Imaging

A Touchy Subject The ability to hold a glass being filled with water without dropping it depends on our ability to touch objects and to know the correct pressure to exert. Thus, for robotics or artificial skin design, methods are needed for sensitive pressure detection. Wu et al. (p. 952, published online 25 April) designed a device based on an array of zinc oxide nanowires that generate a small voltage when flexed that could be translated into a pressure signal. The device has a pressure-sensing range of up to 30 kPa, comparable to the 10 to 40 kPa range of a human finger. An active, addressable pressure-sensitive device facilitates high-resolution tactile imaging. Designing, fabricating, and integrating arrays of nanodevices into a functional system are the key to transferring nanoscale science into applicable nanotechnology. We report large-array three-dimensional (3D) circuitry integration of piezotronic transistors based on vertical zinc oxide nanowires as an active taxel-addressable pressure/force sensor matrix for tactile imaging. Using the piezoelectric polarization charges created at a metal-semiconductor interface under strain to gate/modulate the transport process of local charge carriers, we designed independently addressable two-terminal transistor arrays, which convert mechanical stimuli applied to the devices into local electronic controlling signals. The device matrix can achieve shape-adaptive high-resolution tactile imaging and self-powered, multidimensional active sensing. The 3D piezotronic transistor array may have applications in human-electronics interfacing, smart skin, and micro- and nanoelectromechanical systems.

Triboelectric active sensor array for self-powered static and dynamic pressure detection and tactile imaging.

We report an innovative, large-area, and self-powered pressure mapping approach based on the triboelectric effect, which converts the mechanical stimuli into electrical output signals. The working mechanism of the triboelectric active sensor (TEAS) was theoretically studied by both analytical method and numerical calculation to gain an intuitive understanding of the relationship between the applied pressure and the responsive signals. Relying on the unique pressure response characteristics of the open-circuit voltage and short-circuit current, we realize both static and dynamic pressure sensing on a single device for the first time. A series of comprehensive investigations were carried out to characterize the performance of the TEAS, and high sensitivity (0.31 kPa(-1)), ultrafast response time (<5 ms), long-term stability (30,000 cycles), as well as low detection limit (2.1 Pa) were achieved. The pressure measurement range of the TEAS was adjustable, which means both gentle pressure detection and large-scale pressure sensing were enabled. Through integrating multiple TEAS units into a sensor array, the as-fabricated TEAS matrix was capable of monitoring and mapping the local pressure distribution applied on the device with distinguishable spatial profiles. This work presents a technique for tactile imaging and progress toward practical applications of nanogenerators, providing potential solutions for accomplishment of artificial skin, human-electronic interfacing, and self-powered systems.

Wafer-Scale High-Throughput Ordered Growth of Vertically Aligned ZnO Nanowire Arrays

This article presents an effective approach for patterned growth of vertically aligned ZnO nanowire (NW) arrays with high throughput and low cost at wafer scale without using cleanroom technology. Periodic hole patterns are generated using laser interference lithography on substrates coated with the photoresist SU-8. ZnO NWs are selectively grown through the holes via a low-temperature hydrothermal method without using a catalyst and with a superior control over orientation, location/density, and as-synthesized morphology. The development of textured ZnO seed layers for replacing single crystalline GaN and ZnO substrates extends the large-scale fabrication of vertically aligned ZnO NW arrays on substrates of other materials, such as polymers, Si, and glass. This combined approach demonstrates a novel method of manufacturing large-scale patterned one-dimensional nanostructures on various substrates for applications in energy harvesting, sensing, optoelectronics, and electronic devices.

Strain-Gated Piezotronic Logic Nanodevices

www.MaterialsViews.com C O M Strain-Gated Piezotronic Logic Nanodevices M U N By Wenzhuo Wu , Yaguang Wei , and Zhong Lin Wang * IC A IO N A self-powered [ 1 ] autonomous intelligent nanoscale system should consist of ultrasensitive nanowire (NW) based sensors, [ 2–5 ] integrated high-performance memory and logic computing components for data storage and processing as well as decision making, [ 6–12 ] and an energy scavenging unit for sustainable, self-suffi cient, and independent operation. [ 1 , 13–20 ] The existing semiconductor NW logic devices are based on electrically-gated fi eld-effect transistors, which function as both the drivers and the active loads of the logic units by adjusting the conducting channel width. [ 22 , 23 ] Moreover, the currently existing logic units are “static” and are almost completely triggered or agitated by electric signals, while the “dynamic” movable mechanical actuation is carried out by another unit possibly made of different materials. Here, we present the fi rst piezoelectric triggered mechanicalelectronic logic operation using the piezotronic effect, through which the integrated mechanical electrical coupled and controlled logic computation is achieved using only ZnO NWs. By utilizing the piezoelectric potential created in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) have been fabricated, using which universal logic components such as inverters, NAND, NOR, XOR gates have been demonstrated for performing piezotronic logic calculations, which have the potential to be integrated with the NEMS technology for achieving advanced and complex functional actions in applications of vital importance in portable electronics, medical sciences and defense technology, such as in nanorobotics for sensing and actuating, in microfl uidics [ 24 ] for controlling the circuitry of the fl uid fl ow, in other micro/nano-systems for intelligent control and action. ZnO is unique because of its coupled piezoelectric and semiconductor properties, which is the piezotronic effect dealing with the piezoelectric potential (piezopotential) tuned/gated charge carrier transport process in a semiconductor material. [ 25–27 ] The piezopotential created inside a ZnO NW under strain can be effectively used as a gate voltage, which has been applied for fabricating a range of piezotronic nanodevices, [ 26 , 28 ]

Piezotronic Nanowire-Based Resistive Switches As Programmable Electromechanical Memories

We present the first piezoelectrically modulated resistive switching device based on piezotronic ZnO nanowire (NW), through which the write/read access of the memory cell is programmed via electromechanical modulation. Adjusted by the strain-induced polarization charges created at the semiconductor/metal interface under externally applied deformation by the piezoelectric effect, the resistive switching characteristics of the cell can be modulated in a controlled manner, and the logic levels of the strain stored in the cell can be recorded and read out, which has the potential for integrating with NEMS technology to achieve micro/nanosystems capable for intelligent and self-sufficient multidimensional operations.

Triboelectric Nanogenerator Built on Suspended 3D Spiral Structure as Vibration and Positioning Sensor and Wave Energy Harvester

An unstable mechanical structure that can self-balance when perturbed is a superior choice for vibration energy harvesting and vibration detection. In this work, a suspended 3D spiral structure is integrated with a triboelectric nanogenerator (TENG) for energy harvesting and sensor applications. The newly designed vertical contact-separation mode TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m(2) on a load of 6 MΩ. The position of an in-plane vibration source was identified by placing TENGs at multiple positions as multichannel, self-powered active sensors, and the location of the vibration source was determined with an error less than 6%. The magnitude of the vibration is also measured by the output voltage and current signal of the TENG. By integrating the TENG inside a buoy ball, wave energy harvesting at water surface has been demonstrated and used for lighting illumination light, which shows great potential applications in marine science and environmental/infrastructure monitoring.

Dual-Mode Triboelectric Nanogenerator for Harvesting Water Energy and as a Self-Powered Ethanol Nanosensor

When water is passing through the air or an insulating tube, it will contain not only the mechanical energy but also the electrostatic energy due to the existence of triboelectric charges on its surface as a result of contact with the air/solid surface. In this paper, a hybrid triboelectric nanogenerator (TENG) is designed to simultaneously harvest the electrostatic and mechanical energies of flowing water. Water-TENG, mainly constructed by a superhydrophobic TiO2 layer with hierarchical micro/nanostructures, is used to collect the electrostatic energy of water (Output 1). Contact-TENG, composed by a polytetrafluoroethylene film and a layer of assembled SiO2 nanoparticles, is used to collect the mechanical energy of water (Output 1 and Output 2). Using TiO2 nanomaterials in water-TENG provides the advantages of photocatalytic activity and antibacterial property for water purification. Under the impact of a water stream from a household faucet at a flowing rate of 40 mL s(-1), the generated short-circuit current from Output 1 and Output 2 of dual-mode TENG can reach 43 and 18 μA, respectively. The instantaneous output power densities from Output 1 and Output 2 of dual-mode TENG are 1.31 and 0.38 W m(-2), respectively, when connecting to a load resistor of 44 MΩ. The rectified outputs have been applied to drive light-emitting diodes and charge commercial capacitors. Besides, the water-TENG has also been demonstrated as a self-powered nanosensor for ethanol detection.