uyu Ji

Flexible piezoelectric nanogenerators based on ZnO nanorods grown on common paper substrates.

Nanogenerators capable of harvesting energy from environmental mechanical energy are attractive for many applications. In this paper, we present a simple, low-cost approach to convert low-frequency mechanical energy into electric power using piezoelectric ZnO nanorods grown on a common paper substrate. This energy conversion device has ultrahigh flexibility and piezoelectric sensitivity and can produce an output voltage of up to 10 mV and an output current of about 10 nA. It is demonstrated that the devices electric output behavior can be optionally changed between four types of mode simply by controlling the straining rate. Furthermore, it is also shown that the electric output can be enhanced by scaling the size of the device. This energy-harvesting technology provides a simple and cost-effective platform to capture low-frequency mechanical energy, such as body movements, for practical applications.

Flexible piezoelectric nanogenerator based on Cu2O–ZnO p–n junction for energy harvesting

In this study, a nanogenerator based on Cu2O–ZnO p–n junction has been fabricated on Cu wire substrates for harvesting mechanical energy from the environment. The flexible nanogenerator is composed of a Cu substrate, a Cu2O layer, ZnO nanorods and an outer Au-coated paper electrode; the Cu2O layer was obtained by oxidizing Cu wires directly and the ZnO nanorods were grown on the Cu2O layer using a low-temperature hydrothermal method. The existence of the Cu2O–ZnO p–n junction makes a contribution towards reducing the number of excess electrons in the ZnO, which facilitates in improving the output signal and also overcomes short circuits. An Au-coated paper electrode can involve more nanorods in the power generation process. The DC output voltage was up to 42 mV and the maximum output current density was 400 nA, which are approximately a 13-fold higher voltage and a one order of magnitude larger current in comparison to devices without a Cu2O layer, respectively. This study may provide important insight into a facile fabrication method for low-cost and high-performance energy harvesting devices.

Fabrication of p-NiO/n-ZnO heterojunction devices for ultraviolet photodetectors via thermal oxidation and hydrothermal growth processes

Abstract In this research work, a p-NiO/n-ZnO heterostructure was fabricated using thermal oxidation and hydrothermal growth processes. The p-NiO films were oxidized at different temperatures. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–visible spectral analysis were used to characterize the p-NiO/n-ZnO heterostructure. The results indicated that the NiO films oxidized at higher temperature have wider optical band gap and lower defect density. In particular, by comparing the photoresponse properties of the UV photodetectors oxidized at different temperatures we suggest that the oxidation temperatures have a great influence on the photoresponse time. The defect density of NiO film decreases with increasing oxidation temperature. And the defect density affects the photoresponse characteristics that the decay time decreases with the decreasing of defect density as the NiO oxidation temperature increases. This work could serve as a valuable guideline for designing and improving the p-NiO/n-ZnO UV photodetectors in a low-cost and large-scale way.

Enhanced performance of wearable piezoelectric nanogenerator fabricated by two-step hydrothermal process

A simple two-step hydrothermal process was proposed for enhancing the performance of the nanogenerator on flexible and wearable terylene-fabric substrate. With this method, a significant enhancement in output voltage of the nanogenerator from ∼10 mV to 7 V was achieved, comparing with the one by conventional one-step process. In addition, another advantage with the devices synthesized by two-step hydrothermal process was that their output voltages are only sensitive to strain rather than strain rate. The devices with a high output voltage have the ability to power common electric devices and will have important applications in flexible electronics and wearable devices.

Controlled growth of ZnO nanorods on common paper substrate and their application for flexible piezoelectric nanogenerators

A simple and effective method of synthesizing nanorods (NRs) and the ability to control the size and aspect ratio of them are crucial for fabricating nanodevices. In this paper, we present a systematic study of the growth of ZnO NRs on common paper substrates using a hydrothermal approach by adjusting the growth conditions. By a slight variation of the solution concentration and the growth time, significant changes in morphology and size (aspect ratio) of the obtained ZnO NRs have been controlled. Moreover, the piezoelectric power generation from ZnO-paper nanogenerators grown with different precursor concentration and growth time are also investigated. It is found that the morphology and aspect ratio of NRs have significant influence on the piezoelectric behavior. This type of flexible piezoelectric nanogenerator will have potential applications in implantable biosensors and wearable self-powered electronic devices.

Low-frequency flexible piezoelectric nanogenerators based on ZnO nanorods grown on Cu wires

A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing and personal electronics. In this paper, we present a simple, low-cost approach to convert low-frequency mechanical energy into electric power using piezoelectric ZnO nanorods grown on common Cu wires. This energy conversion device has ultrahigh flexibility and piezoelectric sensitivity and can produce an output current of about 50 nA, which can last for almost 5 seconds. Furthermore, the I–V curves of the device under different strains are also examined, and the I–V characteristic is highly sensitive to strain. This energy-harvesting technology provides a simple and cost-effective platform to capture low-frequency mechanical energy, such as body movements, for practical applications.

Piezoelectric nanogenerator with 3D-ZnO micro-thornyballs prepared by chemical vapour deposition

Piezoelectric nanogenerators have been intensively developed in terms of their materials and applications; however, only modest structural progress has been made due to limitations in the growth mechanisms of nano-materials. In this work, a piezoelectric nanogenerator based on ZnO micro-thornyballs (ZMTBs) was introduced. ZMTBs were synthesized by chemical vapor deposition method without the presence of any seed layers or substrates. Electrical characterization was subsequently performed to reveal the characteristics of the contacts formed between the ZnO micro-thornyballs and the copper electrode. The electric output ability of the ZNTTs nanogenerators has been studied in reference to the experiment and the numerically calculation.

A vibration-driven nanogenerator fabricated on common paper substrate for harvesting energy from environment

There are numerous sources of mechanical energy in our environment, such as ultrasonic waves, body movement, and irregular air flow/vibration. Here, we present a simple, cost-effective approach for fabricating a flexible nanogenerator and apply it to harvest energy from environmental mechanical vibrations. The nanogenerator was based on ZnO nanorods grown on common paper substrate using a low-temperature hydrothermal method. Piezoelectric currents were measured by attaching the nanogenerator on the surface of a cantilever and a wind-up drum, respectively. At the same time, the vibrations of the cantilever and wind-up drum could also be characterized by the corresponding output signals. This is a practical and versatile technology with the potential for converting a variety of environment energy into electric energy, and also with the application for pre-warning of emergency, such as earthquake and burgling.

Piezoelectric effect of 3-D ZnO nanotetrapods

In this work the piezoelectric effect of 3-D ZnO nanotetrapods (ZNTs) is studied by the finite element method. The results show that the nanogenerator based on ZnO nanotetrapods has a number of advantages over the generators based on traditional hexagonal nanorods due to the unique tetrapod structure. Different from double-terminal sensors, the sensors based on ZnO nanotetrapods can give multiple responses to a single signal at the same time. Therefore, ZnO nanotetrapods could be designed as multiterminal strain sensors for enhancing sensitivity and directivity. Here we demonstrate that lateral bending of ZnO nanotetrapods (ZNTs) results in higher output piezopotentials than vertical compression. Effect of geometric size on piezopotential is also studied. The results provide guidance for optimizing the output of piezoelectric nanogenerators and designing high-performance strain sensors.

Photoluminescence and Raman analysis of ZnO microwires synthesized by chemical vapour deposition

ZnO microwires have been synthesized by a simple chemical vapour deposition method. The morphology and optical properties were investigated by scanning electron microscopy, photoluminescence, and Raman spectrum, respectively. The strong ultraviolet emission with the weak deep-level emission observed in the photoluminescence spectrum indicates that the ZnO microwires have good optical properties with limited structural defects. In the Raman spectrum, the intense E2 modes indicate that the ZnO microwires have perfect wurtzite structure. Additionally, the red shift of the Raman peaks can be attributed to the lattice distortion and piezoelectric effect of the nanostructures.