Biomimetic bimodal haptic perception using triboelectric effect.

Multimodal haptic perception is essential for enhancing perceptual experiences in augmented reality applications. To date, several artificial tactile interfaces have been developed to perceive pressure and precontact signals, while simultaneously detecting object type and softness with quantified modulus still remains challenging. Here, inspired by the campaniform sensilla on insect antennae, we proposed a hemispherical bimodal intelligent tactile sensor (BITS) array using the triboelectric effect. The system is capable of softness identification, modulus quantification, and material type recognition. In principle, due to the varied deformability of materials, the BITS generates unique triboelectric output fingerprints when in contact with the tested object. Furthermore, owing to the different electron affinities, the BITS array can accurately recognize material type (99.4% accuracy), facilitating softness recognition (100% accuracy) and modulus quantification. It is promising that the BITS based on the triboelectric effect has the potential to be miniaturized to provide real-time accurate haptic information as an artificial antenna toward applications of human-machine integration.

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's 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 a high voltage, which inhibits bacterial reproduction. However, the output performance is the main factor limiting real-world applications of TENGs. Herein, we report a soft-contact fiber-structure TENG to avoid insufficient friction states and to improve the output, especially at a high rotation speed. Rabbit hair, carbon nanotubes, polyvinylidene difluoride film and paper all contain fiber structures that are used to guarantee soft contact between the friction layers and improve the contact state and abrasion problem. Compared with a 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 3440 V, which solves the matching problems when driving high-voltage devices. A TENG-driven ultraviolet sterilization system is then developed. The bactericidal rate of this sterilization system can reach 91%, which significantly reduces the risk of disease spread. This work improves a forward-looking strategy to improve the output and service life of the TENG. It also expands 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.

Metallic glass-based triboelectric nanogenerators.

Surface wear is a major hindrance in the solid/solid interface of triboelectric nanogenerators (TENG), severely affecting their output performance and stability. To reduce the mechanical input and surface wear, solid/liquid-interface alternatives have been investigated; however, charge generation capability is still lower than that in previously reported solid/solid-interface TENGs. Thus, achieving triboelectric interface with high surface charge generation capability and low surface wear remains a technological challenge. Here, we employ metallic glass as one triboelectric interface and show it can enhance the triboelectrification efficiency by up to 339.2%, with improved output performance. Through mechanical and electrical characterizations, we show that metallic glass presents a lower friction coefficient and better wear resistance, as compared with copper. Attributed to their low atomic density and the absence of grain boundaries, all samples show a higher triboelectrification efficiency than copper. Additionally, the devices demonstrate excellent humidity resistance. Under different gas pressures, we also show that metallic glass-based triboelectric nanogenerators can approach the theoretical limit of charge generation, exceeding that of Cu-based TENG by 35.2%. A peak power density of 15 MW·m-2 is achieved. In short, this work demonstrates a humidity- and wear-resistant metallic glass-based TENG with high triboelectrification efficiency.

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.

A method for quantitatively separating the piezoelectric component from the as-received "Piezoelectric" signal.

Polymer-based piezoelectric devices are promising for developing future wearable force sensors, nanogenerators, and implantable electronics, etc. The electric signals generated by them are often assumed as solely coming from the piezoelectric effect. However, triboelectric signals originated from contact electrification between the piezoelectric devices and the contacted objects can produce non-negligible interfacial electron transfer, which is often combined with the piezoelectric signal to give a triboelectric-piezoelectric hybrid output, leading to an exaggerated measured "piezoelectric" signal. Herein, a simple and effective method is proposed for quantitatively identifying and extracting the piezoelectric charge from the hybrid signal. The triboelectric and piezoelectric parts in the hybrid signal generated by a poly(vinylidene fluoride)-based device are clearly differentiated, and their force and charge characteristics in the time domain are identified. This work presents an effective method to elucidate the true piezoelectric performance in practical measurement, which is crucial for evaluating piezoelectric materials fairly and correctly.

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 discharge­induced 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.

Achieving ultrahigh instantaneous power density of 10 MW/m2 by leveraging the opposite-charge-enhanced transistor-like triboelectric nanogenerator (OCT-TENG).

Converting various types of ambient mechanical energy into electricity, triboelectric nanogenerator (TENG) has attracted worldwide attention. Despite its ability to reach high open-circuit voltage up to thousands of volts, the power output of TENG is usually meager due to the high output impedance and low charge transfer. Here, leveraging the opposite-charge-enhancement effect and the transistor-like device design, we circumvent these limitations and develop a TENG that is capable of delivering instantaneous power density over 10 MW/m2 at a low frequency of ~ 1 Hz, far beyond that of the previous reports. With such high-power output, 180 W commercial lamps can be lighted by a TENG device. A vehicle bulb containing LEDs rated 30 W is also wirelessly powered and able to illuminate objects further than 0.9 meters away. Our results not only set a record of the high-power output of TENG but also pave the avenues for using TENG to power the broad practical electrical appliances.

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.