Large-Area Direct Laser-Shock Imprinting of a 3D Biomimic Hierarchical Metal Surface for Triboelectric Nanogenerators

Charges Transfer in Interfaces for Energy Generating

Under the threat of energy crisis and environmental pollution, the technology for sustainable and clean energy extraction has received considerable attention. Owing to the intensive exploration of energy conversion strategies, expanded energy sources are successfully converted into electric energy, including mechanical energy from human motion, kinetic energy of falling raindrops, and thermal energy in the ambient. Among these energy conversion processes, charge transfer at different interfaces, such as solid-solid, solid-liquid, liquid-liquid, and gas-contained interfaces, dominates the power-generating efficiency. In this review, the mechanisms and applications of interfacial energy generators (IEGs) with different interface types are systematically summarized. Challenges and prospects are also highlighted. Due to the abundant interfacial interactions in nature, the development of IEGs offers a promising avenue of inexhaustible and environmental-friendly power generation to solve the energy crisis.

Construction of Triboelectric Series and Chirality Detection of Amino Acids Using Triboelectric Nanogenerator

Triboelectrification necessitates a frictional interaction between two materials, and their contact electrification is characteristically based on the polarity variance in the triboelectric series. Utilizing this fundamental advantage of the triboelectric phenomenon, different materials can be identified according to their contact electrification capability. Herein, an in-depth analysis of the amino acids present in the stratum corneum of human skin is performed and these are quantified regarding triboelectric polarization. The principal focus of this study lies in analyzing and identifying the amino acids present in copious amounts in the stratum corneum to explain their positive behavior during the contact electrification process. Thus, an augmented triboelectric series of amino acids with quantified triboelectric charging polarity by scrutinizing the transfer charge, work function, and atomic percentage is presented. Furthermore, the chirality of aspartic acid as it is most susceptible to racemization with clear consequences on the human skin is detected. The study is expected to accelerate research exploiting triboelectrification and provide valuable information on the surface properties and biological activities of these important biomolecules.

Micro-/Nanohierarchical Structures Physically Engineered on Surfaces: Analysis and Perspective

The high demand for micro-/nanohierarchical structures as components of functional substrates, bioinspired devices, energy-related electronics, and chemical/physical transducers has inspired their in-depth studies and active development of the related fabrication techniques. In particular, significant progress has been achieved in hierarchical structures physically engineered on surfaces, which offer the advantages of wide-range material compatibility, design diversity, and mechanical stability, and numerous unique structures with important niche applications have been developed. This review categorizes the basic components of hierarchical structures physically engineered on surfaces according to function/shape and comprehensively summarizes the related advances, focusing on the fabrication strategies, ways of combining basic components, potential applications, and future research directions. Moreover, the physicochemical properties of hierarchical structures physically engineered on surfaces are compared based on the function of their basic components, which may help to avoid the bottlenecks of conventional single-scale functional substrates. Thus, the present work is expected to provide a useful reference for scientists working on multicomponent functional substrates and inspire further research in this field.

Flat and roll-type translucent anodic porous alumina molds anodized in oxalic acid for UV nanoimprint lithography

There is much interest in UV nanoimprinting as a fabrication method for various functional devices because of its suitability for efficient fine patterning. To form patterns on opaque substrates by UV nanoimprinting, it is essential to use molds through which UV light can pass. In this study, translucent anodic porous alumina (APA) molds for UV nanoimprinting were fabricated by the anodization of an Al substrate. To fabricate a translucent APA mold, an ordered APA film used as a mold for UV nanoimprinting was formed on the surface side of the Al substrate, and then anodization was continued from the back surface of the Al substrate to increase its transparency in the UV spectral range. A gradient change of Al thickness is necessary for the production of a large-area translucent mold, since it lowers the thickness of opaque defects remaining in the mold. The resulting translucent mold was effective for UV nanoimprinting to prepare ordered polymer nanopillar arrays on the surfaces of opaque substrates because the transmittance of the resulting translucent APA mold was 40% at a wavelength of 365 nm, which was confirmed to be sufficiently translucent to polymerize the photocurable monomer used in this study. In addition, it was possible to fabricate roll-type translucent APA molds by using Al pipes as a starting material. A seamless ordered nanopillar array can be effectively formed on a substrate by continuous UV nanoimprinting using the resulting roll-type translucent APA molds. Ordered nanopillar arrays formed on opaque substrates by UV nanoimprinting using translucent APA molds have various potential applications, such as those for forming antireflective and water-repellent surfaces.

An Integrated Solar Panel with a Triboelectric Nanogenerator Array for Synergistic Harvesting of Raindrop and Solar Energy

The triboelectric nanogenerator (TENG) is regarded as an effective strategy for harvesting energy from raindrops, and is a complementary solution with solar cells to achieve all-weather energy harvesting and sustainable energy supply. However, due to the irregularity of natural rainfalls in the volume, frequency, density, and location, designing high-efficiency raindrop TENG (R-TENG) arrays faces great challenges. In this work, a highly transparent, large-area, and high-efficiency R-TENG array with rational material choice, electrode structure, and array distribution is developed for efficiently harvesting irregular raindrop energy. The problem of electrical signal cancellation among adjacent raindrops can be fully avoided, as viewed from the high-resolution space-time analyses of high-speed camera and electrical signal characteristics. With the rationally designed electrode instead of multiple complex electrodes, all charges can be exported by the R-TENG array in a simulated irregular raindrop scenario. Moreover, it is demonstrated that the R-TENG possesses higher average power density (40.80 mW m^-2 ) than that of the solar cell (37.03 mW m^-2 ) in rainy condition. Additionally, a self-powered wireless light-intensity-monitoring system is demonstrated for real-time and all-day weather monitoring. This work provides useful guidance for designing high-efficiency TENG arrays integrated with solar panels for harvesting irregular raindrop energy and solar energy.

Silicone-Based Multifunctional Thin Films with Improved Triboelectric and Sensing Performances via Chemically Interfacial Modification

The development of triboelectric nanogenerators (TENGs) technology has advanced in recent years. However, TENG performance is affected by the screened-out surface charge density owing to the abundant free electrons and physical adhesion at the electrode-tribomaterial interface. Furthermore, the demand for flexible and soft electrodes is higher than that for stiff electrodes for patchable nanogenerators. This study introduces a chemically cross-linked (XL) graphene-based electrode with a silicone elastomer using hydrolyzed 3-aminopropylenetriethoxysilanes. The conductive graphene-based multilayered electrode was successfully assembled on a modified silicone elastomer using a cheap and eco-friendly layer-by-layer assembly method. As a proof-of-concept, the droplet-driven TENG with the chemically XL electrode of silicone elastomer exhibited an output power of approximately 2-fold improvement owing to its higher surface charge density than without XL. This chemically XL electrode of silicone elastomer film demonstrated remarkable stability and resistance to repeated mechanical deformations like bending and stretching. Moreover, due to the chemical XL effects, it was used as a strain sensor to detect subtle motions and exhibited high sensitivity. Thus, this cheap, convenient, and sustainable design approach can provide a platform for future multifunctional wearable electronic devices.

Rational Design of Advanced Triboelectric Materials for Energy Harvesting and Emerging Applications

The properties of materials play a significant role in triboelectric nanogenerators (TENGs). Advanced triboelectric materials for TENGs have attracted tremendous attention because of their superior advantages (e.g., high specific surface area, high porosity, and customizable macrostructure). These advanced materials can be extensively applied in numerous fields, including energy harvester, wearable electronics, filtration, and self-powered sensors. Hence, designing triboelectric materials as advanced functional materials is important for the development of TENGs. Herein, the structural modification methods based on electrospinning to improve the triboelectric properties and the latest research progress in this kind of TENGs are systematically summarized. Preparation methods and design trends of nanofibers, microspheres, hierarchical structures, and doping nanomaterials are highlighted. The factors influencing the formation and properties of triboelectric materials are considered. Furthermore, the latest progress on the applications of TENGs is systematically elaborated. Finally, the challenges in the development of triboelectric materials are discussed, thereby guiding researchers in the large-scale application of TENGs.

Triboelectric Nanogenerators for Harvesting Diverse Water Kinetic Energy

The water covering the Earth’s surface not only supports life but also contains a tremendous amount of energy. Water energy is the most important and widely used renewable energy source in the environment, and the ability to extract the mechanical energy of water is of particular interest since moving water is ubiquitous and abundant, from flowing rivers to falling rain drops. In recent years, triboelectric nanogenerators (TENGs) have been promising for applications in harvesting kinetic energy from water due to their merits of low cost, light weight, simple structure, and abundant choice of materials. Furthermore, TENGs can also be utilized as self-powered active sensors for monitoring water environments, which relies on the output signals of the TENGs caused by the movement and composition of water. Here, TENGs targeting the harvest of different water energy sources have been systematically summarized and analyzed. The TENGs for harvesting different forms of water energy are introduced and divided on the basis of their basic working principles and modes, i.e., in the cases of solid–solid and solid–liquid. A detailed review of recent important progress in TENG-based water energy harvesting is presented. At last, based on recent progresses, the existing challenges and future prospects for TENG-based water energy harvesting are also discussed.

Controllable and Scalable Fabrication of Superhydrophobic Hierarchical Structures for Water Energy Harvesting

We report a controllable and scalable fabrication approach for the superhydrophobic hierarchical structures and demonstrate the excellent ability to harvest water energy when applied to water-solid contact triboelectric nanogenerator (TENG). A strategy combined with multiple photolithography and micromolding process was developed to accurately regulate the diameters and the center distances of the two-level micropillars. A variety of hierarchical structures were successfully fabricated and presented the advantages of structure control, large scale, high accuracy, and high consistency. The hydrophobic property characterizations were conducted, and the results indicated that the hierarchical structures showed a larger contact angle than the single-level structures and achieved superhydrophobicity. Then the hierarchical structures were applied to water-TENGs with flowing water continuously dripping on, and the effect of the structure parameter on the triboelectric output was analyzed. The hierarchical structures exhibited a superior ability to harvest water energy than the flat film and the single-level structures due to the enhanced friction area and superhydrophobic property. At a flowing velocity of 8 mL/s, the hierarchical structure generated the output voltage of approximately 34 V and the short-circuit current of around 5 μA. The water-TENG device exhibited a power density peak of 7.56 μW/cm2 with a resistive load of 16.6 MΩ at a flowing velocity of 10 mL/s. These findings shed light on the potential applications of the hierarchical structures-based water-TENGs to water energy harvesting and self-powered sensor devices.

Toward a Better Understanding of Shock Imprinting with Polymer Molds Using a Combination of Numerical Analysis and Experimental Research

In the last decade, a new technique has been developed for the nanoimprinting of thin-metal foils using laser-induced shock waves. Recent studies have proposed replacing metal or silicone molds with inexpensive polymer molds for nanoimprinting. In addition, explosive-derived shock waves provide deeper imprinting than molds, greatly simplifying the application of this technology for mass production. In this study, we focused on explosive-derived shock waves, which persist longer than laser-induced shock waves. A numerical analysis and a set of simplified molding experiments were conducted to identify the cause of the deep imprint. Our numerical analysis has accurately simulated the pressure history and deformation behavior of the workpiece and the mold. Whereas a high pressure immediately deforms the polymer mold, a sustained pressure gradually increases the molding depth of the workpiece. Therefore, the duration of the pressure can be one of the conditions to control the impact imprint phenomenon.

Applications of Nanotechnology in Smart Textile Industry: A Critical Review

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Current trends of using nanotechnology in textile industries.

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Nanotechnology-driven techniques for fabrication and modification of textile fibers.

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Wearable nanotechnology for energy storage, sensing, drug release, optics, electronics and photonics.

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Environmental concerns associated with nanotechnology processed textiles.

Background

In recent years, nanotechnology has been playing an important role in designing smart fabrics. Nanomaterials have been employed to introduce in a sustainable manner, antimicrobial, ultraviolet resistant, electrically conductive, optical, hydrophobic and flame-retardant properties into textiles and garments. Nanomaterial based smart devices are now also being integrated with the textiles so as to perform various functions such as energy harvesting and storage, sensing, drug release and optics. These advancements have found wide applications in the fashion industry and are being developed for wider use in defence, healthcare and on-body energy harnessing applications.

Aim of review

The objective of this work is to provide an insight into the current trends of using nanotechnology in the modern textile industries and to inspire and anticipate further research in this field. This review provides an overview of the most current advances concerning on-body electronics research and the wonders which could be realized by nanomaterials in modern textiles in terms of total energy reliance on our clothes.

Key scientific concepts of review

The work underlines the various methods and techniques for the functionalization of nanomaterials and their integration into textiles with an emphasis on cost-effectiveness, comfort, wearability, energy conversion efficiency and eco-sustainability. The most recent trends of developing various nanogenerators, supercapacitors and photoelectronic devices on the fabric are highlighted, with special emphasis on the efficiency and wearability of the textile. The potential nanotoxicity associated with the processed textiles due to the tendency of these nanomaterials to leach into the environment along with possible remediation measures are also discussed. Finally, the future outlook regarding progress in the integration of smart nano-devices on textile fabrics is provided.

A Single-Droplet Electricity Generator Achieves an Ultrahigh Output Over 100 V Without Pre-Charging

The working principle of the triboelectric nanogenerator (TENG), contact electrification and electrostatic induction, has been used to harvest raindrop energy in recent years. However, the existing research is mainly concentrated on solid-liquid electrification, and adopts traditional electrostatic induction (TEI) for output. As a result, the efficiency of droplet electricity generators (DEGs) is severely constrained. Therefore, previous studies deem that the DEG output is limited by interfacial effects. This study reveals that this view is inappropriate and, in reality, the output strategy is the key bottleneck restricting the DEG performance. Here, a switch effect based on an electric-double-layer capacitor (EDLC) is introduced, and an equivalent circuit model is established to understand its working mechanism. Without pre-charging, a single droplet can generate high voltage over 100 V and the output is directly improved by two-orders of magnitude compared with TEI, which is precisely utilizing the interfacial effect. This work provides insightful perspective and lays solid foundation for DEG applications in large scale.

A Hydrophobic Self-Repairing Power Textile for Effective Water Droplet Energy Harvesting

Triboelectric nanogenerators (TENGs) are useful for harvesting clean and widely distributed water droplet energy with high efficiency. However, the commonly used polymer films in TENGs for water droplet energy harvesting have the disadvantages of poor breathability, poor skin affinity, and irreparable hydrophobicity, which greatly hinder their wearable uses. Here, we report an all-fabric TENG (F-TENG), which not only has good air permeability and hydrophobic self-repairing properties but also shows effective energy conversion efficiency. The hydrophobic surface composed of SiO₂ nanoparticles and poly(vinylidenefluoride-co-hexafluoropropylene)/perfluorodecyltrichlorosilane (PVDF-HFP/FDTS) exhibits a static contact angle of 157° and displays excellent acid and alkali resistance. Because of its low glass transition temperature, PVDF-HFP can facilitate the movement of FDTS molecules to the surface layer under heating conditions, realizing hydrophobic self-repairing performance. Furthermore, with the optimized compositions and structure, the water droplet F-TENG shows 7-fold enhancement of output voltage compared with the conventional single-electrode mode TENG, and a total energy conversion efficiency of 2.9% is achieved. Therefore, the proposed F-TENG can be used in multifunctional wearable devices for raindrop energy harvesting.

Highly Efficient Raindrop Energy-Based Triboelectric Nanogenerator for Self-Powered Intelligent Greenhouse

Establishing a sustainable energy supply is necessary for intelligent greenhouse environmental management. Compared with traditional energy, green and eco-friendly energy is more conducive to protecting the agricultural production environment. In this study, a fluorinated superhydrophobic greenhouse film is proposed as a negative triboelectric layer material for the construction of a triboelectric nanogenerator that harvests raindrop energy (RDE-TENG). Moreover, an upgraded configuration is adopted, where the bulk effect between the lower/upper electrode and film replaces the interfacial effect of the liquid-solid interface, thereby promoting charge transfer. The results show that the RDE-TENG can serve as a sustainable energy source for greenhouse temperature and humidity sensors that assists in realizing intelligent control of the environment and guides agricultural production processes. This device exhibits high-voltage and a stable output; thus, it has the potential to replace traditional energy sources, which helps toward realizing a self-powered intelligent greenhouse planting mode.

Air-gap embedded triboelectric nanogenerator via surface modification of non-contact layer using sandpapers

With the increased number of small electronics and demand for their energy source, renewable energy sources have received much attention. Above all, a triboelectric nanogenerator (TENG) based on the combination of contact electrification and electrostatic induction has been researched as a method of converting mechanical energy into electricity. In order to increase the electrical output of TENGs with raising the surface charge density, a lot of researchers have focused on the fabrication methods to employ micro-/nano-structures onto a contact surface of the TENG, but have been facing several issues regarding the degradation of the output performance from the iterative operation process. Hence, it is highly required to introduce an approach to enhancing the performance of TENG, while minimally degrading the output power during the long-term operation. In this paper, an air-gap embedded TENG (AE-TENG), which contains a microstructure on the non-contact surface by means of a sandpaper, is proposed. These small air-gaps between the spin-coated polydimethylsiloxane and the non-contact surface can significantly boost the total surface charge density of the dielectric layer. Thus, the electrical output performance of the AE-TENG is enhanced without any surface engineering on the contact surface. Furthermore, the effect of the air-gap induced surface charges on the electric potential is systematically analyzed by not only experimentally electrical outputs, but theoretical and computational modeling based on the V-Q-x relationship and simulation software tool. This air-gap induced triboelectric effect opens a new perspective of the development of electrical outputs by providing a structural/theoretical understanding for TENGs.

Alternate-Layered MXene Composite Film-Based Triboelectric Nanogenerator with Enhanced Electrical Performance

The output power of the triboelectric nanogenerator (TENG) strongly depends on the performance of triboelectric materials, especially microstructures and functional groups of them. In this work, aiming at the excellent triboelectric ability, alternate-layered MXene composite films-based TENG with abundant fluorine groups(-F) through layer-by-layer stacking are designed and fabricated. Benefitting from the uniform intrinsic microstructure and increased dielectric constant, when the amount of the Nb₂CT_x nanosheets increases to 15 wt%, the TENG based on Nb₂CT_x/Ti₃C₂T_x composite nanosheets films achieves the maximum output. The short-circuit current density of 8.06 μA/cm² and voltage of 34.63 V are 8.4 times and 3.5 times over that of pure Ti₃C₂T_x films, and 3.3 times and 4.3 times over that of commercial poly(tetrafluoroethylene) (PTFE) films, respectively. Furthermore, the fabricated TENG could be attached to human body to harvest energy from human motions, such as typing, texting, and hand clapping. The results demonstrate that the alternate-layered MXene composite nanosheet films through layer-by-layer stacking possess remarkably triboelectric performance, which broaden the choice of negative triboelectric materials and supply a new choice for high output TENG.

UV-Protective, Self-Cleaning, and Antibacterial Nanofiber-Based Triboelectric Nanogenerators for Self-Powered Human Motion Monitoring

Equipping wearable electronics with special functions will endow them with more additional values and more comprehensive practical performance. Here, we report an ultraviolet (UV)-protective, self-cleaning, antibacterial, and self-powered all-nanofiber-based triboelectric nanogenerator (TENG) for mechanical energy harvesting and self-powered sensing, which is fabricated with Ag nanowires (NWs)/TPU nanofibers and the TiO₂@PAN networks through a facile electrospinning method. Due to the added TiO₂ nanoparticles (NPs), the TENG presents excellent UV-protective performance, including the ultraviolet protection factor (UPF) of ∼204, the transmittance of UVA (T_UVA) of ∼0.0574%, and the transmittance of UVB (T_UVB) ∼0.107%. Furthermore, under solar lighting for 25 min, most surface contamination can be degraded, and the decreased power output would be recovered. Owing to the coupled effects of TiO₂ NPs and Ag NWs, the TENG shows excellent antibacterial activity against Staphylococcus aureus. Due to the micro-to-nano hierarchical porous structure, the all-nanofiber-based TENG can serve as self-powered pedometers for detecting and tracking human motion behaviors. As a multifunctional self-powered device, the TENG prompts various applications in the fields of micro/nanopower sources, human movement monitoring, and human-machine interfaces, potentially providing an alternative energy solution and a multifunctional interactive platform for the next-generation wearable electronics.

Carbon nanotube/polydimethylsiloxane composite micropillar arrays using non-lithographic silicon nanowires as a template for performance enhancement of triboelectric nanogenerators

Carbon nanotube/polydimethylsiloxane composite micropillar (CNT/PDMS MP) arrays were successfully fabricated using non-lithographic silicon nanowire (SiNW) arrays as a template for performance enhancement of triboelectric nanogenerators (TENG). The CNT/PDMS MP arrays were obtained by pouring CNT/PDMS composites on the SiNW arrays and peeled off. Surface topology of CNT/PDMS composites directly depends on morphology of SiNW arrays, which can be varied by the etching time of the typical metal-assisted chemical etching process. The micropatterned CNT/PDMS composites was mostly depicted to the SiNW array template pattern when the morphologies of the SiNW were optimized with a length of approximately 10 mm. Next, the CNT/PDMS MP arrays were utilized as a triboelectric layer of TENGs, generating the maximum output voltage of 22.84 ± 0.85 V, enabling an approximately 18-fold improvement in an electrical output compared to the flat PDMS-based TENG. The performance enhancement of TENGs based on CNT/PDMS MP arrays are attributed to synergic effects of (1) an enhancement of electrostatic induction by CNT composites, increasing dielectric constant, and (2) an enhancement of electrification by surface texturing using non-lithographic pattern and CNT composites.

Parallel Nanoimprint Forming of One-Dimensional Chiral Semiconductor for Strain-Engineered Optical Properties

The low-dimensional, highly anisotropic geometries, and superior mechanical properties of one-dimensional (1D) nanomaterials allow the exquisite strain engineering with a broad tunability inaccessible to bulk or thin-film materials. Such capability enables unprecedented possibilities for probing intriguing physics and materials science in the 1D limit. Among the techniques for introducing controlled strains in 1D materials, nanoimprinting with embossed substrates attracts increased attention due to its capability to parallelly form nanomaterials into wrinkled structures with controlled periodicities, amplitudes, orientations at large scale with nanoscale resolutions. Here, we systematically investigated the strain-engineered anisotropic optical properties in Te nanowires through introducing a controlled strain field using a resist-free thermally assisted nanoimprinting process. The magnitude of induced strains can be tuned by adjusting the imprinting pressure, the nanowire diameter, and the patterns on the substrates. The observed Raman spectra from the chiral-chain lattice of 1D Te reveal the strong lattice vibration response under the strain. Our results suggest the potential of 1D Te as a promising candidate for flexible electronics, deformable optoelectronics, and wearable sensors. The experimental platform can also enable the exquisite mechanical control in other nanomaterials using substrate-induced, on-demand, and controlled strains.

Self-Powered Bio-Inspired Spider-Net-Coding Interface Using Single-Electrode Triboelectric Nanogenerator

Human-machine interfaces are essential components between various human and machine interactions such as entertainment, robotics control, smart home, virtual/augmented reality, etc. Recently, various triboelectric-based interfaces have been developed toward flexible wearable and battery-less applications. However, most of them exhibit complicated structures and a large number of electrodes for multidirectional control. Herein, a bio-inspired spider-net-coding (BISNC) interface with great flexibility, scalability, and single-electrode output is proposed, through connecting information-coding electrodes into a single triboelectric electrode. Two types of coding designs are investigated, i.e., information coding by large/small electrode width (L/S coding) and information coding with/without electrode at a predefined position (0/1 coding). The BISNC interface shows high scalability with a single electrode for detection and/or control of multiple directions, by detecting different output signal patterns. In addition, it also has excellent reliability and robustness in actual usage scenarios, since recognition of signal patterns is in regardless of absolute amplitude and thereby not affected by sliding speed/force, humidity, etc. Based on the spider-net-coding concept, single-electrode interfaces for multidirectional 3D control, security code systems, and flexible wearable electronics are successfully developed, indicating the great potentials of this technology in diversified applications such as human-machine interaction, virtual/augmented reality, security, robotics, Internet of Things, etc.

Progress on wearable triboelectric nanogenerators in shapes of fiber, yarn, and textile

Textile has been known for thousands of years for its ease of use, comfort, and wear resistance, which resulted in a wide range of applications in garments and industry. More recently, textile emerges as a promising substrate for self-powered wearable power sources that are desired in wearable electronics. Important progress has been attained in the exploitation of wearable triboelectric nanogenerators (TENGs) in shapes of fiber, yarn, and textile. Along with the effective integration of other devices such as supercapacitor, lithium battery, and solar cell, their feasibility for realizing self-charging wearable systems has been proven. In this review, according to the manufacturing process of traditional textiles starting from fibers, twisting into yarns, and weaving into textiles, we summarize the progress on wearable TENGs in shapes of fiber, yarn, and textile. We explicitly discuss the design strategies, configurations, working mechanism, performances, and compare the merits of each type of TENGs. Finally, we present the perspectives, existing challenges and possible routes for future design and development of triboelectric textiles.

Scalable Nanoshaping of Hierarchical Metallic Patterns with Multiplex Laser Shock Imprinting Using Soft Optical Disks

Large-area patterning of metals in nanoscale has always been a challenge. Traditional microfabrication processes involve many high-cost steps, including etching and high-vacuum deposit, which limit the development of functional nanostructures, especially multiscale metallic patterns. Here, multiplex laser shock imprinting (MLSI) process is introduced to directly manufacture hierarchical micro/nanopatterns at a high strain rate on metallic surfaces using soft optical disks with 1D periodic trenches as molds. The unique metal/polymer layered structures in inexpensive soft optical disks make them strong candidates of molds for MLSI processes. The feasibility of MLSI on hard metals toward soft molds is studied using theoretical simulation. In addition, various types of hierarchical structures are fabricated via MLSI, and their optical reflectance can be modulated via a combination of depth (laser power density), width (types of molds), and angles (rotation between molds). The optical properties have been studied with surface plasmon polariton modes theory. This work opens a new way of manufacturing hierarchical micro/nanopatterns on metals, which is promising for future applications in fields of plasmonics and metasurfaces.

Controlling Surface Charge Generated by Contact Electrification: Strategies and Applications

Contact electrification is the phenomenon in which charge is generated on the surfaces of materials after they come into contact. The surface charge generated has traditionally been known to cause a vast range of undesirable consequences in our lives and in industry; on the other hand, it can also give rise to many types of useful applications. In addition, there has been a lot of interest in recent years for fabricating devices and materials based on regulating a desired amount of surface charge. It is thus important to understand the general strategies for increasing, decreasing, or controlling the surface charge generated by contact electrification. Herein, the fundamental mechanisms for influencing the amount of charge generated, the methods used for implementing these mechanisms, and some of the recent interesting applications that require regulating the amount of surface charge generated by contact electrification, are briefly summarized.

Skin-touch-actuated textile-based triboelectric nanogenerator with black phosphorus for durable biomechanical energy harvesting

Textiles that are capable of harvesting biomechanical energy via triboelectric effects are of interest for self-powered wearable electronics. Fabrication of conformable and durable textiles with high triboelectric outputs remains challenging. Here we propose a washable skin-touch-actuated textile-based triboelectric nanogenerator for harvesting mechanical energy from both voluntary and involuntary body motions. Black phosphorus encapsulated with hydrophobic cellulose oleoyl ester nanoparticles serves as a synergetic electron-trapping coating, rendering a textile nanogenerator with long-term reliability and high triboelectricity regardless of various extreme deformations, severe washing, and extended environmental exposure. Considerably high output (~250-880 V, ~0.48-1.1 µA cm^-2) can be attained upon touching by hand with a small force (~5 N) and low frequency (~4 Hz), which can power light-emitting diodes and a digital watch. This conformable all-textile-nanogenerator is incorporable onto cloths/skin to capture the low output of 60 V from subtle involuntary friction with skin, well suited for users' motion or daily operations.

Skin-touch-actuated textile-based triboelectric nanogenerator with black phosphorus for durable biomechanical energy harvesting

Textiles that are capable of harvesting biomechanical energy via triboelectric effects are of interest for self-powered wearable electronics. Fabrication of conformable and durable textiles with high triboelectric outputs remains challenging. Here we propose a washable skin-touch-actuated textile-based triboelectric nanogenerator for harvesting mechanical energy from both voluntary and involuntary body motions. Black phosphorus encapsulated with hydrophobic cellulose oleoyl ester nanoparticles serves as a synergetic electron-trapping coating, rendering a textile nanogenerator with long-term reliability and high triboelectricity regardless of various extreme deformations, severe washing, and extended environmental exposure. Considerably high output (~250-880 V, ~0.48-1.1 µA cm-2) can be attained upon touching by hand with a small force (~5 N) and low frequency (~4 Hz), which can power light-emitting diodes and a digital watch. This conformable all-textile-nanogenerator is incorporable onto cloths/skin to capture the low output of 60 V from subtle involuntary friction with skin, well suited for users' motion or daily operations.

Manipulation of the Superhydrophobicity of Plasma-Etched Polymer Nanostructures

The manipulation of droplet mobility on a nanotextured surface by oxygen plasma is demonstrated by modulating the modes of hydrophobic coatings and controlling the hierarchy of nanostructures. The spin-coating of polytetrafluoroethylene (PTFE) allows for heterogeneous hydrophobization of the high-aspect-ratio nanostructures and provides the nanostructured surface with "sticky hydrophobicity", whereas the self-assembled monolayer coating of perfluorodecyltrichlorosilane (FDTS) results in homogeneous hydrophobization and "slippery superhydrophobicity". While the high droplet adhesion (stickiness) on a nanostructured surface with the spin-coating of PTFE is maintained, the droplet contact angle is enhanced by creating hierarchical nanostructures via the combination of oxygen plasma etching with laser interference lithography to achieve "sticky superhydrophobicity". Similarly, the droplet mobility on a slippery nanostructured surface with the self-assembled monolayer coating of FDTS is also enhanced by employing the hierarchical nanostructures to achieve "slippery superhydrophobicity" with modulated slipperiness.