Xuexian Chen

Synthesis, optical, and magnetic properties of diluted magnetic semiconductor Zn1−xMnxO nanowires via vapor phase growth

Diluted magnetic semiconductor Zn1−xMnxO nanowires were synthesized via an in situ doping of manganese in ZnO nanowires using vapor phase growth at 500 °C. The maximum content of the manganese in the ZnO is around 13 at. %, approaching the maximum thermal equilibrium limit of Mn solubility in ZnO at the growth temperature. Structure and composition analysis revealed that the manganese was doped into the lattice structure, forming solid solution instead of precipitation. Magnetic property measurements revealed that the as-doped Zn1−xMnxO nanowires exhibit ferromagnetic behavior with Curie temperature around 37 K.

Single-Step Fluorocarbon Plasma Treatment-Induced Wrinkle Structure for High-Performance Triboelectric Nanogenerator.

A triboelectric nanogenerator (TENG) has been thought to be a promising method to harvest energy from environment. To date, the utilization of surface structure and material modification has been considered the most effective way to increase its performance. In this work, a wrinkle structure based high-performance TENG is presented. Using the fluorocarbon plasma treatment method, material modification and surface structure are introduced in one step. The output ability of TENG is dramatically enhanced. After the optimization of plasma treatment, the maximum current and surface charge density are 182 μA about 165 μC m(-2). Compared with untreated TENG, the wrinkle structure makes the current and surface charge density increase by 810% and 528%, separately. X-ray photoelectron spectroscopy is employed to analyze the chemical modification mechanism of this fluorocarbon plasma treatment. Facilitated by its high output performance, this device could directly light 76 blue light emitting diodes under finger typing. The output electric energy could be stored then utilized to power a commercial calculator. As a result of the simple fabrication process and high output ability, devices fabricated using this method could bring forward practical applications using TENGs as power sources.

Integrated self-charging power unit with flexible supercapacitor and triboelectric nanogenerator

With the rapid development of wearable devices and portable electronics, highly efficient and stable self-powered systems are in great demand. However, most harvesting and storage devices of such systems are separate units, which reduce the power density and limit their applications. In this work, we implemented an integrated sandwich-shaped, self-charging power unit (SCPU) with a wrinkled PDMS-based triboelectric nanogenerator and CNT/paper-based solid-state supercapacitor. During ambient vibration process, this SCPU could simultaneously harvest and store energy, efficiently converting mechanical energy into electrochemical energy. The self-charging capability of this SCPU is demonstrated by periodic compressive stress, charging 900 mV within 3 h. Additionally, using three serially connected SCPUs as power supply, it could drive a commercial calculator working continuously and an electrochromic device as a smart window during the coloration and bleaching processes. Considering its efficient structure and facile fabrication, this novel integrated SCPU provides a feasible solution for sustainable power supply and shows great potential in micro-energy fields and self-powered systems.

Highly Compressible Integrated Supercapacitor–Piezoresistance-Sensor System with CNT–PDMS Sponge for Health Monitoring

Rapid improvement of wearable electronics stimulates the demands for the matched functional devices and energy storage devices. Meanwhile, wearable microsystem requires every parts possessing high compressibility to accommodate large-scale mechanical deformations and complex conditions. In this work, a general carbon nanotube-polydimethylsiloxane (CNT-PDMS) sponge electrode is fabricated as the elementary component of the compressible system. CNT-PDMS sponge performs high sensitivity as a piezoresistance sensor, which is capable of detecting stress repeatedly and owns great electrochemical performance as a compressible supercapacitor which maintains stably under compressive strains, respectively. Assembled with the piezoresistance sensor and the compressible supercapacitor, such highly compressible integrated system can power and modulate the low-power electronic devices reliably. More importantly, attached to the epidermal skin or clothes, it can detect human motions, ranging from speech recognition to breathing record, thus showing feasibility in real-time health monitor and human-machine interfaces.

An ultrathin stretchable triboelectric nanogenerator with coplanar electrode for energy harvesting and gesture sensing

Stretchable electronics with excellent elastic characteristics are attracting extensive interest in the area of wearable devices and epidermal electronics. Here, we demonstrate an ultrathin stretchable triboelectric nanogenerator (s-TENG) with coplanar electrode for harvesting diverse biomechanical energies and acting as a self-powered gesture sensor. The s-TENG employs electrospun polyurethane nanofibers and conductive nanomaterials as the stretchable electrode. With the coplanar electrode configuration, the device can generate electricity from diverse working situations, such as folding/unfolding of the device and contact/separation with other objects. Facilitated by the increased contact area of nanostructure and paired electrodes design, the s-TENG can generate enhanced instantaneous peak power density of 316.4 μW cm−2 when working in the folding/unfolding situation. When in contact with other objects such as cotton cloth and human skin, peak voltages of 330 V and 286 V are obtained, respectively. Thanks to the ultrathin structure of the device, it can be conformally attached on skin and deforms as the body moves. By adjusting the dimensions of the device, the s-TENG can be used to detect human motion in different body parts, showing its great application prospects in sustainable wearable devices, self-powered electronic skins and smart wireless sensor networks.

All-fabric-based wearable self-charging power cloth

We present an all-fabric-based self-charging power cloth (SCPC), which integrates a fabric-based single-electrode triboelectric generator (STEG) and a flexible supercapacitor. To effectively scavenge mechanical energy from the human motion, the STEG could be directly woven among the cloth, exhibiting excellent output capability. Meanwhile, taking advantage of fabric structures with a large surface-area and carbon nanotubes with high conductivity, the wearable supercapacitor exhibits high areal capacitance (16.76 mF/cm2) and stable cycling performance. With the fabric configuration and the aim of simultaneously collecting body motion energy by STEG and storing in supercapacitors, such SCPC could be easily integrated with textiles and charged to nearly 100 mV during the running motion within 6 min, showing great potential in self-powered wearable electronics and smart cloths.

High performance triboelectric nanogenerators with aligned carbon nanotubes

As the essential element of a triboelectric nanogenerator (TENG), friction layers play key roles that determine the device performance, which can be enhanced by material selection and surface modification. In this work, we have embedded aligned carbon nanotubes (CNTs) on the polydimethylsiloxane (PDMS) surface as the effective dielectric layer to donate electrons. This layer not only increases the electron generation for the output, but also shows notable stretchability. The length and the properties of the aligned CNTs can be controlled precisely. Using the 40 μm CNT as an example, the fabricated CNT-PDMS TENG shows an output voltage of 150 V and a current density of 60 mA m-2, which are 250% and 300% enhancement compared to the TENG using directly doped PDMS/multiwall carbon nanotubes, respectively. The maximum power density of this TENG reaches 4.62 W m-2 at an external load of 30 MΩ. The TENG has demonstrated superior stability during cyclic measurement of over 12 000 cycles. Besides, the aligned CNT-PDMS film shows superhydrophobicity (154°) and good sheet resistance of 280 Ω sq-1. This stretchable aligned CNT-PDMS film can be universally utilized as a positive triboelectric layer pairing with polymeric materials such as polyethylene terephthalate, polyimide, PDMS and polytetrafluoroethylene for TENGs. This work provides an effective method of structure design for flexible and stretchable nanogenerators.

Controlled fabrication of nanoscale wrinkle structure by fluorocarbon plasma for highly transparent triboelectric nanogenerator

In this paper, we report a novel nanoscale wrinkle-structure fabrication process using fluorocarbon plasma on poly(dimethylsiloxane) (PDMS) and Solaris membranes. Wrinkles with wavelengths of hundreds of nanometers were obtained on these two materials, showing that the fabrication process was universally applicable. By varying the plasma-treating time, the wavelength of the wrinkle structure could be controlled. Highly transparent membranes with wrinkle patterns were obtained when the plasma-treating time was <125 s. The transmittances of these membranes were >90% in the visible region, making it difficult to distinguish them from a flat membrane. The deposited fluorocarbon polymer also dramatically reduced the surface energy, which allowed us to replicate the wrinkle pattern with high precision onto other membranes without any surfactant coating. The combined advantages of high electron affinity and high transparency enabled the fabricated membrane to improve the performance of a triboelectric nanogenerator. This nanoscale, single-step, and universal wrinkle-pattern fabrication process, with the functionality of high transparency and ultra-low surface energy, shows an attractive potential for future applications in micro- and nanodevices, especially in transparent energy harvesters.

A flexible and wearable generator with fluorocarbon plasma induced wrinkle structure

This work presents a flexible and wearable energy harvester for harvesting muscle motion energy. A novel single-step fluorocarbon plasma induced wrinkle structure is employed as the friction layer to increase its performance by enlarging the contact area and introducing material modification at the same time. Under bending or pressing, this device could produce an alternating current. Additionally, by adjusting the spin-coating speed, this wrinkle morphology and the thickness of PDMS (polydimethylsiloxane) film could be controlled. Therefore, through the optimizing of this parameter, 225 V peak voltage and 375 μA maximum current is achieved under finger typing. Moreover, this device is successfully mounted on an adults arm to scavenge the mechanical energy during his motion. Due to its well flexibility, simple manufacturing process, and high output performance, the generator has much potential for powering up wearable electronics or e-skin.

Liquid metal droplet based tube-shaped electrostatic energy harvester

This paper presents a liquid metal droplet (LMD) based tube-shaped electrostatic energy harvester, which for the first time, utilize LMD as tribo-electrification material. This device use double-helix electrodes around the tube to obtain cycle transferred charges which multiple output frequency and enhance efficiency tremendously. As using the tube-shaped structure, this generator can be wound up to users wrist, which is very convenience to harvest energy from human movement. The voltage output can be reached to 3.52 V when user swung arm irregularly. It gives great potential to power up the wearable electronics.