A Compact-Sized Fully Self-Powered Wireless Flowmeter Based on Triboelectric Discharge

Flow sensing exhibits significant potential for monitoring, controlling, and optimizing processes in industries, resource management, and environmental protection. However, achieving wireless real-time and omnidirectional sensing of gas/liquid flow on a simple, self-contained device without external power support has remained a formidable challenge. In this study, a compact-sized, fully self-powered wireless sensing flowmeter (CSWF) is introduced with a small size diameter of down to less than 50 mm, which can transmit real-time and omnidirectional wireless signals, as driven by a rotating triboelectric nanogenerator (R-TENG). The R-TENG triggers the breakdown discharge of a gas discharge tube (GDT), which enables flow rate wireless sensing through emitted electromagnetic waves. Importantly, the performance of the CSWF is not affected by the R-TENG's varied output, while the transmission distance is greater than 10 m. Real-time wireless remote monitoring of wind speed and water flow rate is successfully demonstrated. This research introduces an approach to achieve a wireless, self-powered environmental monitoring system with a diverse range of potential applications, including prolonged meteorological observations, marine environment monitoring, early warning systems for natural disasters, and remote ecosystem monitoring.

High-performance self-desalination powered by triboelectric-electromagnetic hybrid nanogenerator

Freshwater is an essential resource in today's world, and how to produce freshwater with low or even zero power consumption is a major challenge. Here, a desalination system powered by a triboelectric-electromagnetic hybrid nanogenerator (TEHG) is presented, which can utilize the water's own energy to remove the salt ions from itself, demonstrating a new concept of "self-desalination". At a relatively low rotation speed of 150 rpm, the system can dilute NaCl brine from 4000 ppm to 145 ppm with a high salt removal rate of 147.1 μg cm-2 min-1 and a freshwater productivity of up to 31.1 L m-2 h-1. The actual seawater can also be treated with a total ion removal efficiency of 99.6 % and a freshwater productivity of 2.7 L m-2 h-1, which is superior to other renewable-energy-powered desalination systems. More importantly, fully self-powered desalination process can be realized by manual cranking and hydrokinetic energy impact, both of which are capable of treating 1000 ppm salt feed to the drinking water level. The TEHG-powered desalination system not only provides excellent desalination performance but also addresses the challenges of power consumption and limited capacity, which offers a completely new paradigm of "self-desalination".

Celebrating 60 Years of The Chinese University of Hong Kong: Research Highlights in Nanoscience and Nanotechnology

Recent breakthroughs and advances in nanoscience and nanotechnology have profoundly impacted young-generation education, accelerated knowledge transfer to enhance the quality of life, and improved environmental and economic sustainability. The Chinese University of Hong Kong (CUHK), a globally recognized education and research institute, has played a crucial role in promoting major strategic research directions in nanoscience, including translational biomedicine and information and automation technology, as well as environment and sustainability. To celebrate the 60th Anniversary of CUHK, we present this Virtual Issue that showcases the cutting-edge research at CUHK published in ACS Nano.

Passive Internet of Events Enabled by Broadly Compatible Self-Powered Visualized Platform Toward Real-Time Surveillance

Surveillance is an intricate challenge worldwide especially in those complicated environments such as nuclear plants, banks, crowded areas, barns, etc. Deploying self-powered wireless sensor nodes can increase the system's event detection capabilities by collecting environmental changes, while the incompatibility among components (energy harvesters, sensors, and wireless modules) limits their application. Here, a broadly compatible self-powered visualized platform (SPVP) is reported to construct a passive internet of events (IoE) network for surveillance systems. By encoding electric signals into reference and working LEDs, SPVP can visualize resistance change generated by commercial resistive sensors with a broad working range (<107  Ω) and the transmission distance is up to 30 meters. Visible light signals are captured by surveillance cameras and processed by the cloud to achieve real-time event monitoring and identification, which forms the passive IoE network. It is demonstrated that the passive-IoE-based surveillance system can detect intrusion, theft, fire alarm, and distress signals quickly (30 ms) for 106 cycles. Moreover, the confidential information can be encrypted by SPVPs and accessed through a phone application. This universal scheme may have huge potential for the construction of safe and smart cities.

Excellent-Moisture-Resistance Fluorinated Polyimide Composite Film and Self-Powered Acoustic Sensing

As a clean, sustainable energy source, sound can carry a wealth of information and play a huge role in the Internet of Things era. In recent years, triboelectric acoustic sensors have received increasing attention due to the advantages of self-power supply and high sensitivity. However, the triboelectric charge is susceptible to ambient humidity, which reduces the reliability of the sensor and limits the application scenarios significantly. In this paper, a highly moisture-resistant fluorinated polyimide composited with an amorphous fluoropolymer film was prepared. The charge injection performance, triboelectric performance, and moisture resistance of the composite film were investigated. In addition, we developed a self-powered, highly sensitive, and moisture-resistant porous-structure acoustic sensor based on contact electrification. The detection characteristics of the acoustic sensor are also obtained.

High output soft-contact fiber-structure triboelectric nanogenerator and its sterilization application

Infectious diseases are spreading rapidly with the flow of the world population, and the prevention of epidemic diseases is particularly important for public and personal health. Therefore, there is an urgent need to develop a simple, efficient, and non-toxic method to control the spread of bacteria and viruses. The newly developed triboelectric nanogenerator (TENG) can generate high voltage, which inhibits bacterial reproduction. However, the output performance is the main factor limiting the real-world applications of the TENGs. Herein, we report a soft-contact fiber-structure TENG to avoid insufficient friction states and to improve the outputs, especially at a high rotation speed. Rabbit hair, carbon nanotubes, PVDF film, and paper all contain fiber structures, which are used to guarantee soft contact between the friction layers and improve the contact state and abrasion problem. Compared with the direct-contact triboelectric nanogenerator, the outputs of this soft-contact fiber-structure TENG are improved by about 350%. Meanwhile, the open circuit voltage can be enhanced to 3500 V, which solves the matching problems when driving high-voltage devices, and then a TENG-driven ultraviolet sterilization system is developed. The bactericidal rate of this sterilization system can reach 91%, which significantly reduces the risk of disease breeding. This work has improved a forward-looking strategy to improve the outputs and service life of TENG. It has also expanded the applications of self-powered TENG sterilization systems.

Ultrastrong yet Ductile 2D Titanium Nanomaterial for On-Skin Conformal Triboelectric Sensing

Conventional titanium (e.g., bulk or thin films) is well-known for its relatively high mechanical strength, excellent corrosion resistance, and superior biocompatibility, which are suitable for biomedical engineering and wearable devices. However, the strength of conventional titanium often trades off its ductility, and their use in wearable devices has not been explored yet. In this work, we fabricated a series of large-sized 2D titanium nanomaterials with the method of polymer surface buckling enabled exfoliation (PSBEE), which possess a unique heterogeneous nanostructure containing nanosized titanium, titanium oxide, and MXene-like phases. As a result, these 2D titaniums exhibit both superb mechanical strength (6-13 GPa) and remarkable ductility (25-35%) at room temperature, outperforming all other titanium-based materials reported so far. More interestingly, we demonstrate that the 2D titanium nanomaterials also showed good performance in triboelectric sensing and can be used to fabricate self-powered, on-skin conformal triboelectric sensors with good mechanical reliability.

Universal Energy Solution for Triboelectric Sensors Toward the 5G Era and Internet of Things

The launching of 5G technology provides excellent opportunity for the prosperous development of Internet of Things (IoT) devices and intelligent wireless sensor nodes. However, deploying of tremendous wireless sensor nodes network presents a great challenge to sustainable power supply and self-powered active sensing. Triboelectric nanogenerator (TENG) has shown great capability for powering wireless sensors and work as self-powered sensors since its discovery in 2012. Nevertheless, its inherent property of large internal impedance and pulsed "high-voltage and low-current" output characteristic seriously limit its direct application as stable power supply. Herein, a generic triboelectric sensor module (TSM) is developed toward managing the high output of TENG into signals that can be directly utilized by commercial electronics. Finally, an IoT-based smart switching system is realized by integrating the TSM with a typical vertical contact-separation mode TENG and microcontroller, which is able to monitor the real-time appliance status and location information. Such design of a universal energy solution for triboelectric sensors is applicable for managing and normalizing the wide output range generated from various working modes of TENGs and suitable for facile integration with IoT platform, representing a significant step toward scaling up TENG applications in future smart sensing.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

The shift of percent excess mortality from zero-COVID policy to living-with-COVID policy in Singapore, South Korea, Australia, New Zealand and Hong Kong SAR

Introduction

With the economic recession and pandemic fatigue, milder viral variants and higher vaccine coverage along the time lay the basis for lifting anti-COVID policies to restore COVID-19 normalcy. However, when and how to adjust the anti-COVID policies remain under debate in many countries.

Methods

In this study, four countries (Singapore, South Korea, Australia, and New Zealand) and one region (Hong Kong SAR), that have shifted from the zero-COVID (ZC) policy to or close to the living-with-COVID (LWC) during or after the Omicron outbreak, were selected as research objects. All-cause mortality data were collected for these objects from 2009 to 2019. The expected mortality was estimated by a simple linear regression method. Excess mortality over time was calculated as the difference between the expected mortality and the observed mortality. Finally, percent excess mortality (PEM) was calculated as the excess mortality divided by the expected mortality.

Results

In the examined four countries, PEM fluctuated around 0% and was lower than 10% most of the time under the ZC policy before 2022. After shifting to the LWC policy, all the examined countries increased the PEM. Briefly, countries with high population density (Singapore and South Korea) experienced an average PEM of 20-40% during the first half of 2022, and followed by a lower average PEM of 15-18% during the second half of 2022. For countries with low population density under the LWC policy, Australia experienced an average PEM of 39.85% during the first half of 2022, while New Zealand was the only country in our analysis that achieved no more than 10% in average PEM all the time. On the contrary, Hong Kong SAR under their ZC policy attained an average PEM of 71.14% during the first half of 2022, while its average PEM decreased to 9.19% in the second half of 2022 with LWC-like policy.

Conclusion

PEM under different policies within each country/region overtime demonstrated that the mortality burden caused by COVID-19 had been reduced overtime. Moreover, anti-COVID policies are suggested to control the excess mortality to achieve as low as 10% in PEM.

Persistent triboelectrification-induced electroluminescence for self-powered all-optical wireless user identification and multi-mode anti-counterfeiting

Persistent triboelectrification-induced electroluminescence (TIEL) is highly desirable to break the constraints in the transient-emitting behavior of existing TIEL technologies as it addresses the hindrance caused by incomplete information in optical communication. In this work, a novel self-powered persistent TIEL material (SP-PTM) has been created for the first time, by incorporating the long-afterglow phosphors SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) in the material design. It was found that the blue-green transient TIEL derived from ZnS:Cu, Al serves as a reliable excitation source to trigger the persistent photoluminescence (PL) of SAOED. Notably, the aligned dipole moment formed along the vertical direction in the bottom ferroelectric ceramics layer acts as an "optical antenna" to promote variation in the electric field of the upper luminescent layer. Accordingly, the SP-PTM exhibits intense and persistent TIEL for about 10 s in the absence of a continuous power supply. Due to such unique TIEL afterglow behavior, the SP-PTM is applicable in many fields, such as user identification and multi-mode anti-counterfeiting. The SP-PTM proposed in this work not only represents a breakthrough in TIEL materials due to its recording capability and versatile responsivity but also contributes a new strategy to the development of high-performance mechanical-light energy-conversion systems, which may inspire various functional applications.

Porous-Structure-Promoted Tribo-Induced High-Performance Self-Powered Tactile Sensor toward Remote Human-Machine Interaction

Self-powered tactile sensor with versatile functions plays a significant role in the development of an intelligent human-machine interaction (HMI) system. Herein, a hybrid self-powered porous-structured tactile sensor (SPTS) is proposed by monolithically integrating a porous triboelectrification-induced electroluminescence (TIEL) component and a single-electrode triboelectric nanogenerator with the high charge generation in the bulk volume. At a low pressure of 10 kPa, TIEL intensity can be significantly improved by three times, which is superior to that in previous reports, with enhanced triboelectricity. Based on the enhancement brought by the porous structure and optimized parameters, the SPTS achieves significant sensing performance in both optical and electrical modes. To demonstrate the potential of practical applications, a programmable optical and electrical dual-mode HMI system is established based on SPTS to remotely control an intelligent vehicle and operate a computer game through identifying finger touch trajectories. This work not only contributes a new economical-effective methodology toward a high-performance tribo-induced self-powered tactile sensor but also facilitates the remote control of HMI with dual-mode functionality, which has broad potential applications in the fields of intelligent robots, augmented reality, flexible wearable electronics, and smart home.

Understanding the Time-Lag Behavior of the Breakdown-Discharge Voltage

As the world enters the era of the Internet of Things (IoT), wireless devices and their networks become essential fundamental components. Recently, with the rapid development of the triboelectric nanogenerator (TENG), breakdown discharge has become an emerging hot topic in the field since it is the key limiting factor of the output performance, and it may also trigger new applications such as self-powered wireless sensing. However, understandings of the discharge behaviors in TENG are still limited. This study proposed a method to study the breakdown discharge with a large serial resistance and discovered the time-lag behavior of the breakdown discharge. A model based on the Eyring equation is demonstrated to explain this time-lag phenomenon. A convenient method to adjust the breakdown-discharge voltage is developed through this study. As an application, a wireless spark switch being modulated by a series-connected resistance is designed, which may be potentially utilized in wireless applications.

Density of Surface States: Another Key Contributing Factor in Triboelectric Charge Generation

The triboelectric nanogenerator (TENG) has been invented as a technology for harvesting mechanical energy, as well as for allocating quantized charge for scientific instruments. The charge generation of the TENG is mainly related to the triboelectric effect or contact electrification (CE) as usually described by the potential-well-electron-cloud model, while the triboelectric charge transfer is related to the difference in the occupied energy levels of electrons. However, in our experiment, we observed an abnormal triboelectric charge generation phenomena between ternary materials, which cannot be explained by the occupied energy level difference only. To address this issue, we proposed the model based on the density of surface states (DOSS) as another key contributing factor to the triboelectric charge generation. To demonstrate our model, we introduced an approach to measure the DOSS through applying external electric field between two triboelectric surfaces. Our experiments confirmed the contribution of the DOSS to the triboelectric charge generation, with the derived charge density consistent with the measured results, which verified our model. We also predicted that the FEP has the potential to achieve a high charge density of ∼5.6 × 10^-4 C/m², which is close to the reported maximum values. This study provides another key contributing factor to the triboelectric charge generation, which may provide a more complete model for guiding the material selection and modification to tailor the surface charge generated by the CE.

A paradigm shift fully self-powered long-distance wireless sensing solution enabled by discharge-induced displacement current

The rapid development of the Internet of Things depends on wireless devices and their network. Traditional wireless sensing and transmission technology still requires multiple modules for sensing, signal modulation, transmission, and power, making the whole system bulky, rigid, and costly. Here, we proposed a paradigm shift wireless sensing solution based on the breakdown discharge–induced displacement current. Through that, we can combine the abovementioned functional modules in a single unit of self-powered wireless sensing e-sticker (SWISE), which features a small size (down to 9 mm by 9 mm) and long effective transmission distance (>30 m) when compared to existing wireless sensing technologies. Furthermore, SWISEs have functions of multipoint motion sensing and gas detection in fully self-powered manner. This work proposes a solution for flexible self-powered wireless sensing platforms, which shows great potential for implantable and wearable electronics, robotics, health care, infrastructure monitoring, human-machine interface, virtual reality, etc.

Tribo-charge enhanced hybrid air filter masks for efficient particulate matter capture with greatly extended service life

Face masks have been an effective and indispensable personal protective measure against particulate matter pollutants and respiratory diseases, especially the novel Coronavirus disease recently. However, disposable surgical face masks suffer from low filtration efficiency for particles ranging from nano- to micro-size, and the limited service life of ~ 4 h. Here, a nano/micro fibrous hybrid air filter mask composing of electrospun nanofibrous network and poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) coated polypropylene (PP) is proposed. Furthermore, the resultant filter is supplied with tribo-charges by a freestanding sliding triboelectric nanogenerator. Through the enhanced synergistic effect of mechanical interception and electrostatic forces, the hybrid air filter demonstrates high filtration efficiency for particle size of 11.5 nm to 2.5 µm, with a 9.3-34.68% enhancement for particles of 0.3-2.5 µm compared to pristine PP, and 48-h stable filtration efficiency of 94% (0.3-0.4 µm) and 99% (1-2.5 µm) with a low pressure drop of ~110 Pa. In addition, sterilization ability of the tribo-charge enhanced air filter is demonstrated. This work provides a facile and cost-effective approach for state-of-the-art face masks toward high filtration performance of nano- to micro- particles with greatly extended service life.

Tribo-Induced Color Tuner toward Smart Lighting and Self-Powered Wireless Sensing

The color-tuning capability of solid-state lighting (SSL) systems are highly demanded for smart lighting according to the environmental conditions, as well as wireless sensing of the environmental information. In the meanwhile, state-of-the-art triboelectric nanogenerator (TENG)-based sensing systems rely on bulky and expensive devices, which require cable connections and additional power consumptions. This work aims at solving these challenges, through developing a tribo-induced color tuner that can be integrated into the vastly distributed commercial SSL system. This tribo-induced color tuner includes a concentric color conversion plate consisting of (Sr,Ca)AlSiN3:Eu phosphor and TiO2, a tribo-induced liquid lens, and a rotary freestanding sliding TENG. The color oscillation between purple and pink is achieved upon the tribo-charging by the TENG, which reveals the input mechanical motion signals. The signal can be conveniently sent by everywhere-existed lamps and processed by everyone-owned smartphone cameras or closed-circuit televisions. Through this approach, the function of wireless sensing is achieved without the need of preamplification, with no additional power supply required, as demonstrated for wireless sensing of the rotation speed. The smart lighting for underwater photographing is also demonstrated by the color-tunable SSL system with the best imaging quality achieved.

Tribo-Induced Smart Reflector for Ultrasensitive Self-Powered Wireless Sensing of Air Flow

Air-flow sensing is essential in broad applications of weather forecasting, ocean monitoring, gas leakage alarming, and health monitoring. However, in severe environments where electrical power supply and cable connection are not available, the sensing of air flow in a self-powered way is a challenging issue. In this work, we reported a tribo-induced smart reflector to achieve the self-powered wireless sensing of the air flow by combining an aerodynamics-driven triboelectric nanogenerator (TENG) and a silver-coated polymer network liquid crystal. Upon being driven by the air flow, the developed reflector performed specular and diffused reflectance without and with charging by the TENG, respectively, enabling wireless sensing through mechanical-electrical-optical signal conversion. In the developed sensing paradigm, the sensing module can be fully self-powered without the need of signal pre-amplification, which is electrically separated from the light source and detection modules without cable connections. The applications of self-powered wireless wind speed sensing and breath monitoring were performed to demonstrate the effectiveness of the developed paradigm toward self-powered wireless sensing nodes in the internet of things.

Boosting the Output Performance of the Triboelectric Nanogenerator through the Nonlinear Oscillator

The rapid development of the internet of things and autonomous vehicles requires plenty of sensors to monitor environmental conditions continuously. Hence, the high energy density and reliable power supply are demanded. The nonlinear oscillator has been widely utilized to enhance the output performance of piezoelectric and electromagnetic energy harvesters, which can operate in high-energy orbits under proper excitation frequencies. Here, the nonlinear oscillator-based triboelectric nanogenerator (NL-TENG) is proposed based on the grating structure. The mechanism to boost the output of the NL-TENG is analyzed and discussed with an electromechanical coupling model proposed, and the impacts of excitation frequency, external resistance, and spring stiffness were investigated. The peak power of the fabricated NL-TENG is 22 mW, which is 3 times enlarged compared to the traditional linear configuration. Furthermore, the stable and continuous power output of up to 244 W/m³ is demonstrated, which can power a calculator and a large quantity of light-emitting diodes persistently. This study presents a new perspective to boost the output of the TENG by utilizing the benefits from the nonlinear oscillator.

Fully Biodegradable Water Droplet Energy Harvester Based on Leaves of Living Plants

Triboelectric nanogenerators (TENGs) have obtained soaring interest due to their capability for environmental energy harvesting. However, as a harvester for green energy, the frequent adoption of the hardly degradable plastic films is not desirable. Here, we report a fully biodegradable TENG (FBD-TENG) that all elements are made from natural substances, and the utilization of plastic materials is avoided. The leaf cuticle and the inside conductive tissue are utilized as the tribo-material and electrode for one part in the FBD-TENG, and water droplets are employed as the counterpart. By using water droplets to bridge the originally disconnected components into a closed-loop electrical system, we successfully collect energy from the droplet impact onto a plant leaf. The electricity generation phenomenon and the working mechanism of the FBD-TENG have been investigated. Five kinds of plants, as well as rain water droplets, are employed to demonstrate the wide availability of the proposed approach. This study provides a strategy to utilize the pervasively presented electrostatic charges in nature in an eco-friendly way.

Achieving Ultrahigh Output Energy Density of Triboelectric Nanogenerators in High-Pressure Gas Environment

Through years of development, the triboelectric nanogenerator (TENG) has been demonstrated as a burgeoning efficient energy harvester. Plenty of efforts have been devoted to further improving the electric output performance through material/surface optimization, ion implantation or the external electric circuit. However, all these methods cannot break through the fundamental limitation brought by the inevitable electrical breakdown effect, and thus the output energy density is restricted. Here, a method for enhancing the threshold output energy density of TENGs is proposed by suppressing the breakdown effects in the high-pressure gas environment. With that, the output energy density of the contact-separation mode TENG can be increased by over 25 times in 10 atm than that in the atmosphere, and that of the freestanding sliding TENG can also achieve over 5 times increase in 6 atm. This research demonstrates the excellent suppression effect of the electric breakdown brought by the high-pressure gas environment, which may provide a practical and effective technological route to promote the output performance of TENGs.

Carbon Dot-Based Composite Films for Simultaneously Harvesting Raindrop Energy and Boosting Solar Energy Conversion Efficiency in Hybrid Cells

Energy harvesting has drawn worldwide attention as a sustainable technology, while combining several approaches in a single device to maximize the overall energy output holds great promise to offer valuable technologies able to alleviate the energy crisis. Here, we present a hybrid cell composed of a silicon solar cell and a water-droplet-harvesting triboelectric nanogenerator (WH-TENG) with the capacity of harvesting both solar and raindrop energies. A transparent and solution processable carbon dot-based composite film is introduced as a dual-functional layer, acting as the transmittance enhancement layer of the solar cell as well as an ionic conductor of the WH-TENG. At an optimal loading of carbon dots in the composite, the significant enhancement of transmittance in visible spectral range increases the short-circuit current density of the solar cell, which results in an increase of its power conversion efficiency from 13.6% to 14.6%. In addition, the transparent WH-TENG consisting of fluorinated ethylene propylene as a triboelectrification layer can generate a maximum power of 13.9 μW by collecting raindrop energy. This study provides a promising strategy to boost the energy conversion through multiple sources with the aid of a dual-functional layer for enhancing solar cell performance as well as harvesting raindrop energy.

Employing a MEMS plasma switch for conditioning high-voltage kinetic energy harvesters

Triboelectric nanogenerators have attracted wide attention due to their promising capabilities of scavenging the ambient environmental mechanical energy. However, efficient energy management of the generated high-voltage for practical low-voltage applications is still under investigation. Autonomous switches are key elements for improving the harvested energy per mechanical cycle, but they are complicated to implement at such voltages higher than several hundreds of volts. This paper proposes a self-sustained and automatic hysteresis plasma switch made from silicon micromachining, and implemented in a two-stage efficient conditioning circuit for powering low-voltage devices using triboelectric nanogenerators. The hysteresis of this microelectromechanical switch is controllable by topological design and the actuation of the switch combines the principles of micro-discharge and electrostatic pulling, without the need of any power-consuming control electronic circuits. The experimental results indicate that the energy harvesting efficiency is improved by two orders of magnitude compared to the conventional full-wave rectifying circuit.

Conditioning efficiently high-voltage triboelectric nanogenerators for low-voltage applications remains a challenge. Here, the authors demonstrate two orders of magnitude improvement of the energy harvesting efficiency by applying a conditioning circuit with self-sustained and automatic hysteresis MEMS micro-plasma switches.

Multifunctional Self-Powered Switch toward Delay-Characteristic Sensors

With the development of the internet of things (IoT) and 5th generation communication technology, construction of smart cities is making a great progress. However, the IoT system needs millions of sensing nodes; therefore, it is rather challenging to power various sensors. Here, we design an electrostatic force-based switch (EFS) that can work as either an optical or an electrical switch. The EFS provides a method to directly detect or control high-voltage electrical systems with delay characteristics. Advantages of the EFS include self-contained delay characteristics, ease of fabrication, low cost, and high stability, especially when used in combination with the triboelectric nanogenerator (TENG) to realize self-powered sensors. Based on the self-powered sensor, a mechanical motion-sensing system is built with high sensitivity and active response to the mechanical trigger. This study proposes a multifunctional self-powered switch, which realizes a high-voltage delay control system and can also combine with the TENG to expand the application of self-powered smart sensing systems.

Normally Transparent Tribo-Induced Smart Window

Self-powered smart windows are desirable with the expectations of their energy-saving, weather-independent, user-controllable, and miniature performance. Recently developed solar- or thermal-powered smart windows largely depend on the weather conditions and have an extremely slow response, and only a certain portion of the saved energy can be utilized by the external circuit for mode conversion. In this work, a self-powered normally transparent smart window was developed by the conjunction of a rotary freestanding sliding triboelectric nanogenerator (RFS-TENG) and a polymer network liquid crystal (PNLC) cell. To fabricate the PNLC cell, the alignment layer with randomly distributed microdomains was constructed to encapsulate a mixture of LC polymers and nematic LCs. The opacity of the smart window exposed to an alternating electric field was considerably improved owing to the embedded microdomains and a dense web of LC polymers. The ultrahigh haziness greatly alleviates the charge density required for the LC actuation and thus enables the driving by the TENG where the charge amount is usually limited. The RFS-TENG was elaborately designed with six periodic bent triboelectric films and Ag electrodes, which presented an ultralow friction wear and met the frequency requirement to achieve the steady opacity. By harvesting the mechanical energies from ambient environments, the tribo-induced smart window can benefit a wide variety of fields, such as self-powered sunroofs, wind-driven smart farming systems etc.

Inductor-Free Output Multiplier for Power Promotion and Management of Triboelectric Nanogenerators toward Self-Powered Systems

The output voltage of triboelectric nanogenerators (TENGs) is much higher than the overload capacity of most commercial electronics, making it hard to power them directly; so the power-management solution is indispensable. In the meanwhile, it is critical for practical applications to enhance the output performance of the TENG toward its breakdown limit, which is usually ignored before. Here, an inductor-free output multiplier (OM) for power promotion and management of TENGs is proposed, with the breakdown effect considered. This OM, as expanded based on bennet's doubler, is theoretically studied and experimentally demonstrated to significantly enhance the output performance of the TENG within only a few working cycles. The charge output was enhanced by 7.6 times experimentally with the OM. An external capacitor and a switch are applied to realize a high energy extraction ratio of up to 196%, with the average charge output per cycle of ∼3-3.75 μC achieved. This OM circuit with the smart switch is suitable for power promotion of TENGs with variable capacitance and for power management of all TENGs. The OM circuit is demonstrated to ensure the high output performance of TENGs even at a low triboelectric charge density, which is crucial for broad applications of the TENG toward self-powered systems, potentially to be a solution for improving the output performance of TENGs working in harsh environments.

A metal-electrode-free, fully integrated, soft triboelectric sensor array for self-powered tactile sensing

The dramatic advances in flexible/wearable electronics have garnered great attention for touch sensors for practical applications in human health monitoring and human-machine interfaces. Self-powered triboelectric tactile sensors with high sensitivity, reduced crosstalk, and simple processing routes are highly desirable. Herein, we introduce a facile and low-cost fabrication approach for a metal-electrode free, fully integrated, flexible, and self-powered triboelectric tactile sensor array with 8-by-8 sensor units. Through the height difference between the sensor units and interconnect electrodes, the crosstalk derived from the electrodes has been successfully suppressed with no additional shielding layers. The tactile sensor array shows a remarkable sensitivity of 0.063 V kPa^-1 with a linear range from 5 to 50 kPa, which covers a broad range of testing objects. Furthermore, due to the advanced mechanical design, the flexible sensor array exhibits great capability of pressure sensing even under a curved state. The voltage responses from the pattern mapping by finger touching demonstrate the uniformity of the sensor array. Finally, real-time tactile sensing associated with light-emitting diode (LED) array lighting demonstrates the potential application of the sensor array in position tracking, self-powered touch screens, human-machine interfaces and many others.

On the Maximal Output Energy Density of Nanogenerators

Nanogenerators have been demonstrated as a high-efficiency energy harvesting technology, while methods to evaluate merits of nanogenerators are being focused. Energy density, as a common way for evaluating energy devices, is believed to be strongly related to the output performance limit of nanogenerators. Hence, this report introduces an evaluation standard, the output energy density, to evaluate the performance of nanogenerators. With the sliding freestanding mode TENG as an example, theoretical simulations are conducted and experimental methods are developed to understand and optimize the maximal output energy density, with the breakdown effect considered. By comparing the output energy density of TENGs and other nanogenerators, sliding-triggered TENGs are demonstrated with the highest output energy density, which is approaching 1 × 10⁴ J/m³. This study demonstrates the advantages of sliding-triggered TENGs in output energy density due to the suppressed breakdown effect and further confirmed the "killer application" of TENGs in harvesting low-frequency and small-scale mechanical energy.

Raising the Working Temperature of a Triboelectric Nanogenerator by Quenching Down Electron Thermionic Emission in Contact-Electrification

As previously demonstrated, contact-electrification (CE) is strongly dependent on temperature, however the highest temperature in which a triboelectric nanogenerator (TENG) can still function is unknown. Here, by designing and preparing a rotating free-standing mode Ti/SiO₂ TENG, the relationship between CE and temperature is revealed. It is found that the dominant deterring factor of CE at high temperatures is the electron thermionic emission. Although it is normally difficult for CE to occur at temperatures higher than 583 K, the working temperature of the rotating TENG can be raised to 673 K when thermionic emission is prevented by direct physical contact of the two materials via preannealing. The surface states model is proposed for explaining the experimental phenomenon. Moreover, the developed electron cloud-potential well model accounts for the CE mechanism with temperature effects for all types of materials. The model indicates that besides thermionic emission of electrons, the atomic thermal vibration also influences CE. This study is fundamentally important for understanding triboelectrification, which will impact the design and improve the TENG for practical applications in a high temperature environment.

Triboelectric Nanogenerator (TENG) Mass Spectrometry of Falsified Antimalarials

RATIONALE

An epidemic of low quality medicines continues to endanger patients worldwide. Detection of such "medicines" requires low cost, ambient ionization sources coupled to fieldable mass spectrometers for optimum sensitivity and specificity. With the use of triboelectric nanogenerators (TENGs), the charge required to produce gas-phase ions for mass analysis can be obtained without the need for high voltage electrical circuitry, simplifying and lowering the cost of next-generation mass spectrometry instruments.

METHODS

A sliding freestanding (SF) TENG was coupled to a toothpick electrospray setup for the purposes of testing if falsified medicines could be fingerprinted by this approach. Extracts from both genuine and falsified medicines were deposited on the toothpick and the SF TENG actuated to generate electrical charges, resulting in gas-phase ions for both active pharmaceutical ingredients and excipients.

RESULTS

Our previous work had shown that direct analysis in real-time (DART) ambient mass spectrometry can identify the components of multiple classes of falsified antimalarial medicines. Experiments performed in this study show that a simple extraction into methanol along with the use of a SF TENG-powered toothpick electrospray can provide similar detection capabilities, but with much simpler and rugged instrumentation, and without the need for compressed gases or high voltage ion source power supplies.

CONCLUSIONS

TENG toothpick MS allows for rapid analyte ion detection in a safe and low-cost manner, providing robust sampling and ionization capabilities.

Concurrent Harvesting of Ambient Energy by Hybrid Nanogenerators for Wearable Self-Powered Systems and Active Remote Sensing

Harvesting energy available from ambient environment is highly desirable for powering personal electronics and health applications. Due to natural process and human activities, steam can be produced by boilers, human perspiration, and the wind exists ubiquitously. In the outdoor environment, these two phenomena usually exist at the same place, which contain heat and mechanical energies simultaneously. However, previous studies have isolated them as separate sources of energy to harvest and hence failed to utilize them effectively. Herein, we present unique hybrid nanogenerators for individually/simultaneously harvesting thermal energy from water vapors and mechanical energy from intermittent wind blowing from the bottom side, which consist of a wind-driven triboelectric nanogenerator (TENG) and pyroelectric-piezoelectric nanogenerators (PPENGs). The output power of the PPENG and the TENG can be up to about 184.32 μW and 4.74 mW, respectively, indicating the TENG plays the dominant role. Our hybrid nanogenerators could provide different applications such as to power digital watch and enable self-powered sensing with wireless transmission. The device could also be further integrated into a face mask for potentially wearable applications. This work not only provides a promising approach for renewable energy harvesting but also enriches potential applications for self-powered systems and wireless sensors.

High-Output Lead-Free Flexible Piezoelectric Generator Using Single-Crystalline GaN Thin Film

Piezoelectric generators (PEGs) are a promising power source for future self-powered electronics by converting ubiquitous ambient mechanical energy into electricity. However, most of the high-output PEGs are made from lead zirconate titanate, in which the hazardous lead could be a potential risk to both humans and environment, limiting their real applications. III-Nitride (III-N) can be a potential candidate to make stable, safe, and efficient PEGs due to its high chemical stability and piezoelectricity. Also, PEGs are preferred to be flexible rather than rigid, to better harvest the low-magnitude mechanical energy. Herein, a high-output, lead-free, and flexible PEG (F-PEG) is made from GaN thin film by transferring a single-crystalline epitaxial layer from silicon substrate to a flexible substrate. The output voltage, current density, and power density can reach 28 V, 1 μA·cm^-2, and 6 μW·cm^-2, respectively, by bending the F-PEG. The generated electric power by human finger bending is high enough to light commercial visible light-emitting diodes and charge commercial capacitors. The output performance is maintained higher than 95% of its original value after 10 000-cycle test. This highly stable, high-output, and lead-free GaN thin-film F-PEG has the great potential for future self-powered electronic devices and systems.

On the Electron-Transfer Mechanism in the Contact-Electrification Effect

A long debate on the charge identity and the associated mechanisms occurring in contact-electrification (CE) (or triboelectrification) has persisted for many decades, while a conclusive model has not yet been reached for explaining this phenomenon known for more than 2600 years! Here, a new method is reported to quantitatively investigate real-time charge transfer in CE via triboelectric nanogenerator as a function of temperature, which reveals that electron transfer is the dominant process for CE between two inorganic solids. A study on the surface charge density evolution with time at various high temperatures is consistent with the electron thermionic emission theory for triboelectric pairs composed of Ti-SiO₂ and Ti-Al₂ O₃ . Moreover, it is found that a potential barrier exists at the surface that prevents the charges generated by CE from flowing back to the solid where they are escaping from the surface after the contacting. This pinpoints the main reason why the charges generated in CE are readily retained by the material as electrostatic charges for hours at room temperature. Furthermore, an electron-cloud-potential-well model is proposed based on the electron-emission-dominatedcharge-transfer mechanism, which can be generally applied to explain all types of CE in conventional materials.

Lewis-base-catalysed selective reductions of ynones with a mild hydride donor

Nucleophilic phosphines catalyze efficient 1,2-reductions of ynones employing pinacolborane as a mild hydride donor in the presence of alcohol additives.

3D Orthogonal Woven Triboelectric Nanogenerator for Effective Biomechanical Energy Harvesting and as Self-Powered Active Motion Sensors

The development of wearable and large-area energy-harvesting textiles has received intensive attention due to their promising applications in next-generation wearable functional electronics. However, the limited power outputs of conventional textiles have largely hindered their development. Here, in combination with the stainless steel/polyester fiber blended yarn, the polydimethylsiloxane-coated energy-harvesting yarn, and nonconductive binding yarn, a high-power-output textile triboelectric nanogenerator (TENG) with 3D orthogonal woven structure is developed for effective biomechanical energy harvesting and active motion signal tracking. Based on the advanced 3D structural design, the maximum peak power density of 3D textile can reach 263.36 mW m^-2 under the tapping frequency of 3 Hz, which is several times more than that of conventional 2D textile TENGs. Besides, its collected power is capable of lighting up a warning indicator, sustainably charging a commercial capacitor, and powering a smart watch. The 3D textile TENG can also be used as a self-powered active motion sensor to constantly monitor the movement signals of human body. Furthermore, a smart dancing blanket is designed to simultaneously convert biomechanical energy and perceive body movement. This work provides a new direction for multifunctional self-powered textiles with potential applications in wearable electronics, home security, and personalized healthcare.

Piezo-Phototronic Effect on Selective Electron or Hole Transport through Depletion Region of Vis-NIR Broadband Photodiode

Silicon underpins nearly all microelectronics today and will continue to do so for some decades to come. However, for silicon photonics, the indirect band gap of silicon and lack of adjustability severely limit its use in applications such as broadband photodiodes. Here, a high-performance p-Si/n-ZnO broadband photodiode working in a wide wavelength range from visible to near-infrared light with high sensitivity, fast response, and good stability is reported. The absorption of near-infrared wavelength light is significantly enhanced due to the nanostructured/textured top surface. The general performance of the broadband photodiodes can be further improved by the piezo-phototronic effect. The enhancement of responsivity can reach a maximum of 78% to 442 nm illumination, the linearity and saturation limit to 1060 nm light are also significantly increased by applying external strains. The photodiode is illuminated with different wavelength lights to selectively choose the photogenerated charge carriers (either electrons or holes) passing through the depletion region, to investigate the piezo-phototronic effect on electron or hole transport separately for the first time. This is essential for studying the basic principles in order to develop a full understanding about piezotronics and it also enables the development of the better performance of optoelectronics.

Simultaneously Enhancing Light Emission and Suppressing Efficiency Droop in GaN Microwire-Based Ultraviolet Light-Emitting Diode by the Piezo-Phototronic Effect

Achievement of p-n homojuncted GaN enables the birth of III-nitride light emitters. Owing to the wurtzite-structure of GaN, piezoelectric polarization charges present at the interface can effectively control/tune the optoelectric behaviors of local charge-carriers (i.e., the piezo-phototronic effect). Here, we demonstrate the significantly enhanced light-output efficiency and suppressed efficiency droop in GaN microwire (MW)-based p-n junction ultraviolet light-emitting diode (UV LED) by the piezo-phototronic effect. By applying a -0.12% static compressive strain perpendicular to the p-n junction interface, the relative external quantum efficiency of the LED is enhanced by over 600%. Furthermore, efficiency droop is markedly reduced from 46.6% to 7.5% and corresponding droop onset current density shifts from 10 to 26.7 A cm^-2. Enhanced electrons confinement and improved holes injection efficiency by the piezo-phototronic effect are revealed and theoretically confirmed as the physical mechanisms. This study offers an unconventional path to develop high efficiency, strong brightness and high power III-nitride light sources.

Ultralight Cut-Paper-Based Self-Charging Power Unit for Self-Powered Portable Electronic and Medical Systems

The development of lightweight, superportable, and sustainable power sources has become an urgent need for most modern personal electronics. Here, we report a cut-paper-based self-charging power unit (PC-SCPU) that is capable of simultaneously harvesting and storing energy from body movement by combining a paper-based triboelectric nanogenerator (TENG) and a supercapacitor (SC), respectively. Utilizing the paper as the substrate with an assembled cut-paper architecture, an ultralight rhombic-shaped TENG is achieved with highly specific mass/volume charge output (82 nC g^-1/75 nC cm^-3) compared with the traditional acrylic-based TENG (5.7 nC g^-1/5.8 nC cm^-3), which can effectively charge the SC (∼1 mF) to ∼1 V in minutes. This wallet-contained PC-SCPU is then demonstrated as a sustainable power source for driving wearable and portable electronic devices such as a wireless remote control, electric watch, or temperature sensor. This study presents a potential paper-based portable SCPU for practical and medical applications.

Triboelectric nanogenerators for sensitive nano-coulomb molecular mass spectrometry

Ion sources for molecular mass spectrometry are usually driven by direct current power supplies with no user control over the total charges generated. Here, we show that the output of triboelectric nanogenerators (TENGs) can quantitatively control the total ionization charges in mass spectrometry. The high output voltage of TENGs can generate single- or alternating-polarity ion pulses, and is ideal for inducing nanoelectrospray ionization (nanoESI) and plasma discharge ionization. For a given nanoESI emitter, accurately controlled ion pulses ranging from 1.0 to 5.5 nC were delivered with an onset charge of 1.0 nC. Spray pulses can be generated at a high frequency of 17 Hz (60 ms in period) and the pulse duration is adjustable on-demand between 60 ms and 5.5 s. Highly sensitive (∼0.6 zeptomole) mass spectrometry analysis using minimal sample (18 pl per pulse) was achieved with a 10 pg ml^-1 cocaine sample. We also show that native protein conformation is conserved in TENG-ESI, and that patterned ion deposition on conductive and insulating surfaces is possible.

Understanding Self-Catalyzed Epitaxial Growth of III-V Nanowires toward Controlled Synthesis

The self-catalyzed growth of III-V nanowires has drawn plenty of attention due to the potential of integration in current Si-based technologies. The homoparticle-assisted vapor-liquid-solid growth mechanism has been demonstrated for self-catalyzed III-V nanowire growth. However, the understandings of the preferred growth sites of these nanowires are still limited, which obstructs the controlled synthesis and the applications of self-catalyzed nanowire arrays. Here, we experimentally demonstrated that thermally created pits could serve as the preferred sites for self-catalyzed InAs nanowire growth. On that basis, we performed a pregrowth annealing strategy to promote the nanowire density by enhancing the pits formation on the substrate surface and enable the nanowire growth on the substrate that was not capable to facilitate the growth. The discovery of the preferred self-catalyzed nanowire growth sites and the pregrowth annealing strategy have shown great potentials for controlled self-catalyzed III-V nanowire array growth with preferred locations and density.

All-in-One Shape-Adaptive Self-Charging Power Package for Wearable Electronics

Recently, a self-charging power unit consisting of an energy harvesting device and an energy storage device set the foundation for building a self-powered wearable system. However, the flexibility of the power unit working under extremely complex deformations (e.g., stretching, twisting, and bending) becomes a key issue. Here, we present a prototype of an all-in-one shape-adaptive self-charging power unit that can be used for scavenging random body motion energy under complex mechanical deformations and then directly storing it in a supercapacitor unit to build up a self-powered system for wearable electronics. A kirigami paper based supercapacitor (KP-SC) was designed to work as the flexible energy storage device (stretchability up to 215%). An ultrastretchable and shape-adaptive silicone rubber triboelectric nanogenerator (SR-TENG) was utilized as the flexible energy harvesting device. By combining them with a rectifier, a stretchable, twistable, and bendable, self-charging power package was achieved for sustainably driving wearable electronics. This work provides a potential platform for the flexible self-powered systems.

Self-powered textile for wearable electronics by hybridizing fiber-shaped nanogenerators, solar cells, and supercapacitors

Wearable electronics fabricated on lightweight and flexible substrate are believed to have great potential for portable devices, but their applications are limited by the life span of their batteries. We propose a hybridized self-charging power textile system with the aim of simultaneously collecting outdoor sunshine and random body motion energies and then storing them in an energy storage unit. Both of the harvested energies can be easily converted into electricity by using fiber-shaped dye-sensitized solar cells (for solar energy) and fiber-shaped triboelectric nanogenerators (for random body motion energy) and then further stored as chemical energy in fiber-shaped supercapacitors. Because of the all-fiber-shaped structure of the entire system, our proposed hybridized self-charging textile system can be easily woven into electronic textiles to fabricate smart clothes to sustainably operate mobile or wearable electronics.

All-Elastomer-Based Triboelectric Nanogenerator as a Keyboard Cover To Harvest Typing Energy

The drastic expansion of consumer electronics (like personal computers, touch pads, smart phones, etc.) creates many human-machine interfaces and multiple types of interactions between human and electronics. Considering the high frequency of such operations in our daily life, an extraordinary amount of biomechanical energy from typing or pressing buttons is available. In this study, we have demonstrated a highly flexible triboelectric nanogenerator (TENG) solely made from elastomeric materials as a cover on a conventional keyboard to harvest biomechanical energy from typing. A dual-mode working mechanism is established with a high transferred charge density of ∼140 μC/m(2) due to both structural and material innovations. We have also carried out fundamental investigations of its performance dependence on various structural factors for optimizing the electric output in practice. The fully packaged keyboard-shaped TENG is further integrated with a horn-like polypyrrole-based supercapacitor as a self-powered system. Typing in normal speed for 1 h, ∼8 × 10(-4) J electricity could be stored, which is capable of driving an electronic thermometer/hydrometer. Our keyboard cover also performs outstanding long-term stability, water resistance, as well as insensitivity to surface conditions, and the last feature makes it useful to research the typing behaviors of different people.

Harvesting Broad Frequency Band Blue Energy by a Triboelectric-Electromagnetic Hybrid Nanogenerator

Ocean wave associated energy is huge, but it has little use toward world energy. Although such blue energy is capable of meeting all of our energy needs, there is no effective way to harvest it due to its low frequency and irregular amplitude, which may restrict the application of traditional power generators. In this work, we report a hybrid nanogenerator that consists of a spiral-interdigitated-electrode triboelectric nanogenerator (S-TENG) and a wrap-around electromagnetic generator (W-EMG) for harvesting ocean energy. In this design, the S-TENG can be fully isolated from the external environment through packaging and indirectly driven by the noncontact attractive forces between pairs of magnets, and W-EMG can be easily hybridized. Notably, the hybrid nanogenerator could generate electricity under either rotation mode or fluctuation mode to collect energy in ocean tide, current, and wave energy due to the unique structural design. In addition, the characteristics and advantages of outputs indicate that the S-TENG is irreplaceable for harvesting low rotation speeds (<100 rpm) or motion frequencies (<2 Hz) energy, which fits the frequency range for most of the water wave based blue energy, while W-EMG is able to produce larger output at high frequencies (>10 Hz). The complementary output can be maximized and hybridized for harvesting energy in a broad frequency range. Finally, a single hybrid nanogenerator unit was demonstrated to harvest blue energy as a practical power source to drive several LEDs under different simulated water wave conditions. We also proposed a blue energy harvesting system floating on the ocean surface that could simultaneously harvest wind, solar, and wave energy. The proposed hybrid nanogenerator renders an effective and sustainable progress in practical applications of the hybrid nanogenerator toward harvesting water wave energy offered by nature.

A highly shape-adaptive, stretchable design based on conductive liquid for energy harvesting and self-powered biomechanical monitoring

The rapid growth of deformable and stretchable electronics calls for a deformable and stretchable power source. We report a scalable approach for energy harvesters and self-powered sensors that can be highly deformable and stretchable. With conductive liquid contained in a polymer cover, a shape-adaptive triboelectric nanogenerator (saTENG) unit can effectively harvest energy in various working modes. The saTENG can maintain its performance under a strain of as large as 300%. The saTENG is so flexible that it can be conformed to any three-dimensional and curvilinear surface. We demonstrate applications of the saTENG as a wearable power source and self-powered sensor to monitor biomechanical motion. A bracelet-like saTENG worn on the wrist can light up more than 80 light-emitting diodes. Owing to the highly scalable manufacturing process, the saTENG can be easily applied for large-area energy harvesting. In addition, the saTENG can be extended to extract energy from mechanical motion using flowing water as the electrode. This approach provides a new prospect for deformable and stretchable power sources, as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, and entertainment.

Harvesting Low-Frequency (<5 Hz) Irregular Mechanical Energy: A Possible Killer Application of Triboelectric Nanogenerator

Electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) are the two most powerful approaches for harvesting ambient mechanical energy, but the effectiveness of each depends on the triggering frequency. Here, after systematically comparing the performances of EMGs and TENGs under low-frequency motion (<5 Hz), we demonstrated that the output performance of EMGs is proportional to the square of the frequency, while that of TENGs is approximately in proportion to the frequency. Therefore, the TENG has a much better performance than that of the EMG at low frequency (typically 0.1-3 Hz). Importantly, the extremely small output voltage of the EMG at low frequency makes it almost inapplicable to drive any electronic unit that requires a certain threshold voltage (∼0.2-4 V), so that most of the harvested energy is wasted. In contrast, a TENG has an output voltage that is usually high enough (>10-100 V) and independent of frequency so that most of the generated power can be effectively used to power the devices. Furthermore, a TENG also has advantages of light weight, low cost, and easy scale up through advanced structure designs. All these merits verify the possible killer application of a TENG for harvesting energy at low frequency from motions such as human motions for powering small electronics and possibly ocean waves for large-scale blue energy.

Role of microRNA-129-5p in osteoblast differentiation from bone marrow mesenchymal stem cells

Mesenchymal stem cells derived from bone marrow have the capacity to differentiate into osteoblast, chondrocyte, nerve cell and myocardial cell in vitro, which are an ideal engraft in tissue-engineered repair. Osteoblast differentiation is a vital process in maintaining bone homeostasis in which various transcriptional factors, including signaling molecules, and microRNAs (miRNAs). In this research, human bone marrow mesenchymal stem cells (hBMSCs) were induced differentiation into osteoblast in vitro after over-expression of miR-129-5p. The results showed that the hBMSCs could induce differentiation into osteoblast under the special condition medium, but when the miR-129-5p was over-expressed in hBMSCs, the differentiated efficiency and induced time of osteoblast from hBMSCs could be promoted. This reason was demonstrated that signal transducer and activator of transcription 1 (STAT1) was a transcriptional repressor of osteoblast gene (Runx 2) expression during osteoblast differentiation, miR-129-5p reduced STAT1 levels, leading to the accumulation of correctly spliced Runx 2 mRNA and a dramatic increase in Runx 2 protein.

Excluding Contact Electrification in Surface Potential Measurement Using Kelvin Probe Force Microscopy

Kelvin probe force microscopy (KPFM), a characterization method that could image surface potentials of materials at the nanoscale, has extensive applications in characterizing the electric and electronic properties of metal, semiconductor, and insulator materials. However, it requires deep understanding of the physics of the measuring process and being able to rule out factors that may cause artifacts to obtain accurate results. In the most commonly used dual-pass KPFM, the probe works in tapping mode to obtain surface topography information in a first pass before lifting to a certain height to measure the surface potential. In this paper, we have demonstrated that the tapping-mode topography scan pass during the typical dual-pass KPFM measurement may trigger contact electrification between the probe and the sample, which leads to a charged sample surface and thus can introduce a significant error to the surface potential measurement. Contact electrification will happen when the probe enters into the repulsive force regime of a tip-sample interaction, and this can be detected by the phase shift of the probe vibration. In addition, the influences of scanning parameters, sample properties, and the probe's attributes have also been examined, in which lower free cantilever vibration amplitude, larger adhesion between the probe tip and the sample, and lower cantilever spring constant of the probe are less likely to trigger contact electrification. Finally, we have put forward a guideline to rationally decouple contact electrification from the surface potential measurement. They are decreasing the free amplitude, increasing the set-point amplitude, and using probes with a lower spring constant.