Synthesis of Ultrathin Copper Nanowires Using Tris(trimethylsilyl)silane for High-Performance and Low-Haze Transparent Conductors

Bioinspired Multiscale Mineralization: From Fundamentals to Potential Applications

The wondrous and imaginative designs of nature have always been an inexhaustible treasure trove for material scientists. Throughout the long evolutionary process, biominerals with hierarchical structures possess some specific advantages such as outstanding mechanical properties, biological functions, and sensing performances, the formation of which (biomineralization) is delicately regulated by organic component. Provoked by the subtle structures and profound principles of nature, bioinspired functional minerals can be designed with the participation of organic molecules. Because of the designable morphology and functions, multiscale mineralization has attracted more and more attention in the areas of medicine, chemistry, biology, and material science. This review provides a summary of current advancements in this extending topic. The mechanisms underlying mineralization is first concisely elucidated. Next, several types of minerals are categorized according to their structural characteristic, as well as the different potential applications of these materials. At last, a comprehensive overview of future developments for bioinspired multiscale mineralization is given. Concentrating on the mechanism of fabrication and broad application prospects of multiscale mineralization, the hope is to provide inspirations for the design of other functional materials.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

In the era of Internet-of-things, many things can stay connected; however, biological systems, including those necessary for human health, remain unable to stay connected to the global Internet due to the lack of soft conformal biosensors. The fundamental challenge lies in the fact that electronics and biology are distinct and incompatible, as they are based on different materials via different functioning principles. In particular, the human body is soft and curvilinear, yet electronics are typically rigid and planar. Recent advances in materials and materials design have generated tremendous opportunities to design soft wearable bioelectronics, which may bridge the gap, enabling the ultimate dream of connected healthcare for anyone, anytime, and anywhere. We begin with a review of the historical development of healthcare, indicating the significant trend of connected healthcare. This is followed by the focal point of discussion about new materials and materials design, particularly low-dimensional nanomaterials. We summarize material types and their attributes for designing soft bioelectronic sensors; we also cover their synthesis and fabrication methods, including top-down, bottom-up, and their combined approaches. Next, we discuss the wearable energy challenges and progress made to date. In addition to front-end wearable devices, we also describe back-end machine learning algorithms, artificial intelligence, telecommunication, and software. Afterward, we describe the integration of soft wearable bioelectronic systems which have been applied in various testbeds in real-world settings, including laboratories that are preclinical and clinical environments. Finally, we narrate the remaining challenges and opportunities in conjunction with our perspectives.

Improved Performance in Li-S Batteries Due to In Situ CuS Formation from Cu Nanowires

Lithium-sulfur batteries offer theoretical capacities of 800-1600 mAh g-1 of active material and are therefore one of the most promising new battery chemistries currently under intensive study. However, the low electronic conductivity of the sulfur and the discharge products imposes energy penalties during the discharge and charge steps. In addition, the reduction of sulfur during discharge forms soluble polysulfides, which will diffuse to, and react with, the lithium metal anode. To address these two challenges, copper nanowires were introduced into the composite cathode to improve the electronic conductivity of the cathode and to provide electrostatic anchoring points for the formed polysulfide anions. The addition of the conductive copper nanowires resulted in the in situ formation of copper sulfide, which was shown to decrease the resistivity of the SEI layer on the anode, as manifested by diminished lithium plating and stripping overpotentials. Higher copper loadings exacerbated the dissolution of the copper sulfide during deep discharge and increased the concentration of displaced capping ligands in the electrolyte. Both phenomena generate species that react at the lithium anode, resulting in a more resistive SEI layer.

Conductive Nanofiber Web Film with Polydimethylsiloxane Sidewalls Selectively Coated through a Plasma Process for High Performance Flexible Transparent Electrodes

Transparent electrodes are commonly used in various applications, such as solar cells, touch screens, smart windows, wearable electronic devices, and rollable flexible displays. Currently, indium tin oxide (ITO) is widely used as a transparent electrode material. However, ITO is not suitable for next-generation transparent electrodes that require flexibility; therefore, alternative nanomaterials, such as carbon nanotubes, conductive polymers, and metal nanowires, are being studied. However, these nanomaterials have poor mechanical strength and limited substrate availability. In this study, we developed a high-performance transparent electrode web film fabrication process based on conductive nanofibers, in which metal nanofibers are semiembedded in polydimethylsiloxane (PDMS). The mechanical strength of the conductive nanofibers was improved through the PDMS coating on the entire surface of the film, and the semiembedded structure of the nanofibers was realized using the reactive ion etching (RIE) process. In this study, we confirmed through transparency/conductivity analysis and bending, cycle, and taping tests that the transparent electrode fabricated using our approach has excellent mechanical strength and conductivity. Finally, the transparent electrode fabricated using our method can be widely applied as a next-generation transparent electrode because the process is easy and simple and requires inexpensive equipment and materials.

Recent Advances in Biodegradable Green Electronic Materials and Sensor Applications

As environmental issues have become the dominant agenda worldwide, the necessity for more environmentally friendly electronics has recently emerged. Accordingly, biodegradable or nature-derived materials for green electronics have attracted increased interest. Initially, metal-green hybrid electronics are extensively studied. Although these materials are partially biodegradable, they have high utility owing to their metallic components. Subsequently, carbon-framed materials (such as graphite, cylindrical carbon nanomaterials, graphene, graphene oxide, laser-induced graphene) have been investigated. This has led to the adoption of various strategies for carbon-based materials, such as blending them with biodegradable materials. Moreover, various conductive polymers have been developed and researchers have studied their potential use in green electronics. Researchers have attempted to fabricate conductive polymer composites with high biodegradability by shortening the polymer chains. Furthermore, various physical, chemical, and biological sensors that are essential to modern society have been studied using biodegradable compounds. These recent advances in green electronics have paved the way toward their application in real life, providing a brighter future for society.

Direct coating of gold nanolayers to enhance the oxidation resistance of copper nanowire flexible transparent conductive films

Copper nanowire-based transparent conductive films have garnered extensive attention owing to their cost-effectiveness and comparable electrical properties. However, the inherent instability of copper nanowires (Cu NWs) has curtailed their extensive utility and applicability. Herein, we present durable Cu@Au NW/PET films exhibiting elevated photoelectric attributes and remarkable flexibility. After preparing Cu NWs, the purification operation allows the purity of the Cu NWs to reach about 98%. Subsequently, Cu@Au NWs/PET flexible transparent conductive films (FTCFs) were prepared through vacuum filtration of Cu NWs and direct treatment with chloroauric acid. The resulting Cu@Au NW-based FTCFs exhibit impressive attributes including a low sheet resistance of 30 ohms per square and a high optical transmittance of 90%, resulting in an exceptional figure of merit (FOM) of 99. Remarkably, the Cu@Au NWs/PET film showed remarkable flexibility, retaining its properties after 10 000 cycles of continuous bending. Stability assessments further affirm the sheet resistance of the Cu@Au NW FTCFs remains nearly unchanged over 75 days at ambient temperature. The strategic integration of a gold nanolayer, serving as a protective coating on the Cu NWs, yields substantial enhancements in both electrical conductivity and overall stability within the Cu NW FTCF architecture. Furthermore, the obtained Cu@Au NW films exhibit rapid heating capabilities, reaching a temperature of 67 °C within 30 seconds at 3.5 V and subsequently returning to room temperature at the same rate. In summary, the introduction of a Au protective layer can effectively enhance the oxidation resistance of Cu NWs, which has great application potential in FTCFs in the field of film heaters.

Copper Nanowire/Polydopamine-Modified Sodium Alginate Composite Films with Enhanced Long-Term Stability and Adhesion for Flexible Organic Light-Emitting Diodes

Copper nanowire (CuNW), with combined advantages of high conductivity and cost-effectiveness, is considered a promising material for the development of next-generation transparent conductive films (TCFs) in the field of flexible optoelectronics. However, the practical application of CuNW TCFs is hindered by some limitations, such as conductivity degradation and poor adhesion. Here, we demonstrate a stable CuNW composite film by embedding CuNWs into a polydopamine (PDA)-modified sodium alginate (NaAlg) matrix without sacrificing the optoelectronic properties of the CuNW network. The introduction of the PDA modifier significantly enhances the antiaging capability of the NaAlg layer, providing strengthened protection of the embedded CuNWs against moisture and oxygen, thereby resulting in minimal degradation of the conductivity of CuNWs for up to 9 months under ambient conditions. Simultaneously, the interface adhesion between the CuNW network and the substrate is further enhanced due to the abundance of catechol structures in PDA, allowing for the maintenance of the electrical conductivity of the CuNW network even under cyclic external bending stress and tape-peeling forces. In addition, embedding CuNWs into the polymer binding layer produces a CuNW composite film with a very smooth surface. A flexible OLED based on the PDA-modified NaAlg/CuNW TCF is successfully fabricated, exhibiting performance comparable to that of a traditional rigid indium tin oxide-based device, while also demonstrating remarkable mechanical durability. The modification strategy can promote practical applications of the CuNW network in flexible optoelectronic devices.

Flexible triboelectric nanogenerators using transparent copper nanowire electrodes: energy harvesting, sensing human activities and material recognition

Triboelectric nanogenerators (TENGs) have emerged as a promising green technology to efficiently harvest otherwise wasted mechanical energy from the environment and human activities. However, cost-effective and reliably performing TENGs require rational integration of triboelectric materials, spacers, and electrodes. The present work reports for the first time the use of oxydation-resistant pure copper nanowires (CuNWs) as an electrode to develop a flexible, and inexpensive TENG through a potentially scalable approach involving vacuum filtration and lactic acid treatment. A ∼6 cm2 device yields a remarkable open circuit voltage (Voc) of 200 V and power density of 10.67 W m-2 under human finger tapping. The device is robust, flexible and noncytotoxic as assessed by stretching/bending maneuvers, corrosion tests, continuous operation for 8000 cycles, and biocompatibility tests using human fibroblast cells. The device can power 115 light emitting diodes (LEDs) and a digital calculator; sense bending and motion from the human hand; and transmit Morse code signals. The robustness, flexibility, transparency, and non-cytotoxicity of the device render it particularly promising for a wide range of energy harvesting and advanced healthcare applications, such as sensorised smart gloves for tactile sensing, material identification and safer surgical intervention.

Functional Ultrathin Separators Proactively Stabilizing Zinc Anodes for Zinc-Based Energy Storage

Ultrathin separators are indispensable to high-energy-density zinc-ion batteries (ZIBs), but their easy failure caused by zinc dendrites poses a great challenge. Herein, 23 µm-thick functional ultrathin separators (FUSs), realizing superb electrochemical stability of zinc anodes and outstanding long-term durability of ultrathin separators, are reported. In the FUSs, an ultrathin but mechanically strong nanoporous membrane substrate benefits fast and flux-homogenized Zn²⁺ transport, while a metal-organic framework (MOF)-derived C/Cu nanocomposite decoration layer provides rich low-barrier zinc nucleation sites, thereby synergistically stabilizing zinc anodes to inhibit zinc dendrites and dendrite-caused separator failure. Investigation of the zinc affinity of the MOF-derived C/Cu nanocomposites unravels the high zincophilicity of heteroatom-containing C/Cu interfaces. Zinc anodes coupled with the FUSs present superior electrochemical stability, whose operation lifetime exceeds 2000 h at 1 mA cm^-2 and 600 h at 10 mA cm^-2 , 40-50 times longer than that of the zinc anodes using glass-fiber separators. The reliability of the FUSs in ZIBs and zinc-ion hybrid supercapacitors is also validated. This work proposes a new strategy to stabilize zinc anodes and provides theoretical guidance in developing ultrathin separators for high-energy-density zinc-based energy storage.

Colloidal Synthesis of Metal Nanocrystals: From Asymmetrical Growth to Symmetry Breaking

Nanocrystals offer a unique platform for tailoring the physicochemical properties of solid materials to enhance their performances in various applications. While most work on controlling their shapes revolves around symmetrical growth, the introduction of asymmetrical growth and thus symmetry breaking has also emerged as a powerful route to enrich metal nanocrystals with new shapes and complex morphologies as well as unprecedented properties and functionalities. The success of this route critically relies on our ability to lift the confinement on symmetry by the underlying unit cell of the crystal structure and/or the initial seed in a systematic manner. This Review aims to provide an account of recent progress in understanding and controlling asymmetrical growth and symmetry breaking in a colloidal synthesis of noble-metal nanocrystals. With a touch on both the nucleation and growth steps, we discuss a number of methods capable of generating seeds with diverse symmetry while achieving asymmetrical growth for mono-, bi-, and multimetallic systems. We then showcase a variety of symmetry-broken nanocrystals that have been reported, together with insights into their growth mechanisms. We also highlight their properties and applications and conclude with perspectives on future directions in developing this class of nanomaterials. It is hoped that the concepts and existing challenges outlined in this Review will drive further research into understanding and controlling the symmetry breaking process.

Spatially modulated femtosecond laser direct ablation-based preparation of ultra-flexible multifunctional copper mesh electrodes and its application

Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.

An Ultrahigh Rate and Stable Zinc Anode by Facet-Matching-Induced Dendrite Regulation

Resource-abundant metal (e.g., zinc) batteries feature intrinsic advantages of safety and sustainability. Their practical feasibility, however, is impeded by the poor reversibility of metal anodes, typically caused by the uncontrollable dendrite enlargement. Significant effort is exerted to completely prevent dendrites from forming, but this seems less effective at high current densities. Herein, this work presents an alternative dendrite regulation strategy of forming tiny, homogeneously distributed, and identical zinc dendrites by facet matching, which effectively avoids undesirable dendrite enlargement. Confirmed by multiscale theoretical screening and characterization, the regularly exposed Cu(111) facets at the ridges of a copper nanowire are capable of such dendrite regulation by forming a low-mismatched Zn(002)/Cu(111) interface. Consequently, reversible zinc electroplating/stripping is achieved at an unprecedentedly high rate of 100 mA cm^-2 for over 30 000 cycles, corresponding to an accumulative areal capacity up to 30 Ah cm^-2 . A full cell using this anode shows a high capacity of 308.3 mAh g^-1 and a high capacity retention of 91.4% after 800 cycles. This strategy is also viable for magnesium and aluminum anodes, thus opening up a promising and universal avenue toward long-life and high-rate metal anodes.

The Chemistry of Cu3 N and Cu3 PdN Nanocrystals

The precursor conversion chemistry and surface chemistry of Cu₃ N and Cu₃ PdN nanocrystals are unknown or contested. Here, we first obtain phase-pure, colloidally stable nanocubes. Second, we elucidate the pathway by which copper(II) nitrate and oleylamine form Cu₃ N. We find that oleylamine is both a reductant and a nitrogen source. Oleylamine is oxidized by nitrate to a primary aldimine, which reacts further with excess oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with Cu^I to form Cu₃ N. Third, we investigated the surface chemistry and find a mixed ligand shell of aliphatic amines and carboxylates (formed in situ). While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we show that doping with palladium decreases the band gap and the material becomes semi-metallic. These results bring insight into the chemistry of metal nitrides and might help the development of other metal nitride nanocrystals.

Anisotropic Growth of Copper Nanorods Mediated by Cl- Ions

Anisotropic growth to form Cu particles of rod and wire shapes has been obtained typically in a complex system that involves both organic capping agents and Cl- ions. However, the sole effect of Cl- ions on the formation of Cu wires has yet to be fully understood, especially in an organic system. This present work determines the effect of Cl- ions on the morphologies of Cu particles in an organic phase without any capping agents. The results revealed that anisotropic Cu rods could be grown with the sole presence of Cl- ions. The rods have the (011) facets as the long axis, the (111) facets as the tip, and the (100) facets as the side surface. By increasing the Cl- ion concentration, more Cu atoms contributed to the formation of Cu rods and the kinetic growth of the length and the diameter of the rods varied. This suggests that Cl- ions have preferential adsorption on the (100) Cu surfaces to promote the anisotropic growth of Cu. Meanwhile, the adsorption of Cl- to the (111) and (100) surfaces at high Cl- concentrations regulates the relative growth of the particle length and diameter.

Modification of TiAlV Alloys with Hybrid Layers Containing Metallic Nanoparticles Obtained by the Sol-Gel Method: Surface and Structural Properties

The aim of the work was to obtain hybrid coatings containing silver, copper, and zinc nanoparticles on the TiAlV medical alloy via a sol–gel process. The developed layers were designed to bring about a bactericidal and fungicidal effect, as well as for protection against surgical scratches during the implantation of implants used in veterinary medicine. In this work, the authors focused on evaluating the microstructure (SEM + EDS); the structure (XRD, FTIR); and the surface properties, such as wettability, free surface energy, and roughness of layers with various concentrations of metallic nanoparticles (2 and 5 mol %). Our results confirmed that the sol–gel method enables the easy manufacturing of hybrid layers endowed with different porosity values as well as various shapes and sizes of metallic nanoparticles. A higher concentration of nanoparticles was observed on the surface containing 5 mol % of metallic salts. The highest degree of homogeneity was obtained for the layers containing silver nanoparticles. In addition, the silver nanoparticles were round and had the smallest dimensions, even below 20 nm. The FTIR and XRD structural studies confirmed the presence of an organosilicon matrix containing all three types of the metallic particles. We conclude that the higher concentration of nanoparticles influenced the alloy surface parameters.

Novel Fabrication of Silver-Coated Copper Nanowires with Organic Compound Solution

Copper nanowires and Cu-Ag nanowires have various potential applications, such as transparent conductive film, flexible electronics, and conductive filler. In this study, we developed a new green fabrication method for silver-coated copper nanowires using methylsulfonylmethane (DMSO2), which is an environmentally friendly chemical at the food-grade level, to replace toxic chemicals, including ammonia, in the silver coating process. Copper nanowires were synthesized under various reaction temperatures and concentrations of hydrazine (N2H4), ethylenediamine (EDA), sodium hydroxide (NaOH), and copper precursor. The reaction temperature higher than 70 °C caused the oxidation of copper products and evaporation of the sample solution. The optimal conditions to synthesize copper nanowires more than 18 µm in length and 25-45 nm in diameter were determined: 9 M of NaOH, 50 µL of EDA, 17 mM of CuCl2, 5.7 mM of N2H4, and 70 °C reaction temperature. Cu-Ag nanowires, which have about a 12 nm thick silver shell, were successfully fabricated at room temperature under 1 mM of silver nitrate (AgNO3) and 1 wt % of DMSO2. Synthesis conditions for copper and silver-coated copper nanowires have been optimized.

In Situ Partial Sulfidation for Preparing Cu/Cu2−xS Core/Shell Nanorods with Enhanced Photocatalytic Degradation

Herein, we report an approach to prepare Cu/Cu2−xS core/shell nanorods by in situ sulfidation of copper nanorods. Firstly, copper nanorods with tunable longitudinal surface plasmon resonances were synthesized by a seed-mediated method using Au nanoparticles as seeds. A convenient in situ sulfidation method was then applied to convert the outermost layer of Cu nanorods into Cu2−xS, to increase their stability and surface activity in photocatalytic applications. The thickness of Cu2−xS layer can be adjusted by controlling the amount of S source. The Cu/Cu2−xS core/shell nanorods exhibits two characteristic surface plasmon resonances located in visible and near-infrared regions, respectively. The photocatalytic performances of Cu nanorods and their derivatives were evaluated by measuring the degradation rate of methyl orange dyes. Compared with Cu nanorods, the Cu/Cu2−xS core/shell nanorods demonstrate more than a 13.6-fold enhancement in the degradation rate at 40 min. This work suggests a new direction for constructing derivative nanostructures of copper nanorods and exploring their applications.

Epidermis-Inspired Wearable Piezoresistive Pressure Sensors Using Reduced Graphene Oxide Self-Wrapped Copper Nanowire Networks

Wearable piezoresistive sensors are being developed as electronic skins (E-skin) for broad applications in human physiological monitoring and soft robotics. Tactile sensors with sufficient sensitivities, durability, and large dynamic ranges are required to replicate this critical component of the somatosensory system. Multiple micro/nanostructures, materials, and sensing modalities have been reported to address this need. However, a trade-off arises between device performance and device complexity. Inspired by the microstructure of the spinosum at the dermo epidermal junction in skin, a low-cost, scalable, and high-performance piezoresistive sensor is developed with high sensitivity (0.144 kPa-1 ), extensive sensing range ( 0.1-15 kPa), fast response time (less than 150 ms), and excellent long-term stability (over 1000 cycles). Furthermore, the piezoresistive functionality of the device is realized via a flexible transparent electrode (FTE) using a highly stable reduced graphene oxide self-wrapped copper nanowire network. The developed nanowire-based spinosum microstructured FTEs are amenable to wearable electronics applications.

Nanowelding in Whole-Lifetime Bottom-Up Manufacturing: From Assembly to Service

The continuous miniaturization of microelectronics is pushing the transformation of nanomanufacturing modes from top-down to bottom-up. Bottom-up manufacturing is essentially the way of assembling nanostructures from atoms, clusters, quantum dots, etc. The assembly process relies on nanowelding which also existed in the synthesis process of nanostructures, construction and repair of nanonetworks, interconnects, integrated circuits, and nanodevices. First, many kinds of novel nanomaterials and nanostructures from 0D to 1D, and even 2D are synthesized by nanowelding. Second, the connection of nanostructures and interfaces between metal/semiconductor-metal/semiconductor is realized through low-temperature heat-assisted nanowelding, mechanical-assisted nanowelding, or cold welding. Finally, 2D and 3D interconnects, flexible transparent electrodes, integrated circuits, and nanodevices are constructed, functioned, or self-healed by nanowelding. All of the three nanomanufacturing stages follow the rule of "oriented attachment" mechanisms. Thus, the whole-lifetime bottom-up manufacturing process from the synthesis and connection of nanostructures to the construction and service of nanodevices can be organically integrated by nanowelding. The authors hope this review can bring some new perspective in future semiconductor industrialization development in the expansion of multi-material systems, technology pathway for the refined design, controlled synthesis and in situ characterization of complex nanostructures, and the strategies to develop and repair novel nanodevices in service.

N,N-Dimethylformamide-Assisted Shape Evolution of Highly Uniform and Shape-Pure Colloidal Copper Nanocrystals

In this paper, the N,N-dimethylformamide (DMF)-assisted shape evolution of highly uniform and shape-pure copper nanocrystals (Cu NCs) is presented for the first time. Colloidal Cu NCs are synthesized via the disproportionation reaction of copper (I) bromide in the presence of a non-polar solvent mixture. It is observed that the shape of Cu NCs is systematically controlled by the addition of different amounts of DMF to the reaction mixture in high-temperature reaction conditions while maintaining a high size uniformity and shape purity. With increasing amount of DMF in the reaction mixture, the morphology of the Cu NCs change from a cube enclosed by six {100} facets, to a sphere with mixed surface facets, and finally, to an octahedron enclosed by eight {111} facets. The origin of this shape evolution is understood via first-principles density functional theory calculations, which allows the study of the change in the relative surface stability according to surface-coordinating adsorbates. Further, the shape-dependent plasmonic properties are systematically investigated with highly uniform and ligand-exchanged colloidal Cu NCs dispersed in acetonitrile. Finally, the facet-dependent electrocatalytic activities of the shape-controlled Cu NCs are investigated to reveal the activities of the highly uniform and shape-pure Cu NCs in the methanol oxidation reaction.

Copper Nanowires for Transparent Electrodes: Properties, Challenges and Applications

Transparent electrodes are essential elements of devices bearing a screen or display, as well as solar cells, LEDs etc. To overcome the drawbacks presented by indium tin oxide, nanomaterials have been proposed for a long time as alternatives. Metal nanowires are particularly interesting for their high intrinsic electrical conductivity. Copper nanowires have attracted wide interest due to the low cost and high abundancy of the starting material. However, they are easily oxidized thus suitable strategies must be devised to prevent it. This review discusses the fundamental properties and challenges of copper nanowires, focusing on the efforts made to make them longer and thinner then the strategies to prevent oxidation and to join them in the network are presented. After that, mechanical properties are summarized and applications are presented, before conclusions and perspectives are finally given.

Self-Assembly of a Linear Alkylamine Bilayer around a Cu Nanocrystal: Molecular Dynamics

Copper nanocrystals are often grown with the help of alkylamine capping agents, which direct the nanocrystal shape. However, the role of these molecules is still unclear. We characterized the assembly of aqueous tetradecylamine (TDA) around a Cu nanocrystal and found that TDA exhibits a temperature-dependent bilayer structure. The bilayer involves an inner layer, in which TDA binds to Cu via the amine group and tends to orient the alkyl tail perpendicular to the surface, and an outer layer whose structure depends on temperature. At low temperatures, alkylamines in the inner layer form bundles with no apparent relation to the crystal facets. Alkylamines in the outer layer tend to orient their long axes perpendicular to the Cu surfaces, with interdigitation into the inner layer. At high temperatures, alkylamines in the inner layer lose their bundle structure, and outer-layer alkylamines tend to orient themselves tangential to the Cu surfaces, forming a "web" above inner-layer TDA. TDA exhibits a rapid interlayer exchange at typical synthesis temperatures, consistent with experiment. The variety in the assemblies seen here and in other studies of alkanethiols around gold nanocrystals indicates a richness in the assemblies that can be achieved by modulating the interaction between the strongly binding end group and the surface.

High-Performance Flexible Transparent Conductive Films Enabled by a Commonly Used Antireflection Layer

Recently, silver nanowire-based transparent conductive films (AgNW-based TCFs) with excellent comprehensive performance have aroused wide and great interest. However, it is always difficult to simultaneously improve the performances of TCFs in all aspects. In this work, by introducing silica nanoparticles (SiO₂-NPs) with a smaller particle size, several properties of AgNW-based TCFs were optimized successfully. The transmittance and conductivity were improved simultaneously, and smaller particle size was proven to be more suitable to achieve TCFs with excellent optoelectrical properties. Typically, an AgNW/SiO₂-based TCF with a sheet resistance of 250 Ω/sq and transmittance of 93.6% (including the poly (ethylene terephthalate) substrate, abbreviated as PET) could be obtained by using SiO₂-NPs with a size of ∼21 nm, and this transmittance is even higher than that of the bare PET (91.8%) substrate. We demonstrated that the layer formed through self-assembly of SiO₂-NPs can cut down the light scattering on the AgNW surface through total reflection, thus leading to a low haze of AgNW/SiO₂-based TCFs. Very interestingly, the SiO₂-NPs conducted away most of the heat generated during laser ablation, protecting the AgNWs from excessive melt and PET from empyrosis, and thus ensuring the TCFs with high transmittance and patterning accuracy. Besides, AgNW/SiO₂-based TCFs have smaller surface roughness, better flexibility, and adhesive force. To the best of our knowledge, the comprehensive performance of the AgNW/SiO₂-based TCFs reaches the highest level among recently reported novel TCFs.

Heterometallic Seed-Mediated Growth of Monodisperse Colloidal Copper Nanorods with Widely Tunable Plasmonic Resonances

We report a heterometallic seed-mediated synthesis method for monodisperse penta-twinned Cu nanorods using Au nanocrystals as seeds. Elemental analyses indicate that resultant nanorods consist predominantly of copper with a gold content typically below 3 atom %. The nanorod aspect ratio can be readily adjusted from 2.8 to 13.1 by varying the molar ratio between Au seeds and Cu precursor, resulting in narrow longitudinal plasmon resonances tunable from 762 to 2201 nm. Studies of reaction intermediates reveal that symmetry-breaking is promoted by rapid nanoscale diffusion in Au-Cu alloys and the formation of a gold-rich surface. The growth pathway features coevolving shape and composition whereby nanocrystals become progressively enriched with Cu concomitant with nanorod growth. The availability of uniform colloidal Cu nanorods with widely tunable aspect ratios opens new avenues toward the synthesis of derivative one-dimensional metal nanostructures, and applications in surface-enhanced spectroscopy, bioimaging, and electrocatalysis, among others.

Highly transparent and conductive electrodes enabled by scalable printing-and-sintering of silver nanowires

Silver nanowires (Ag NWs) have good promised for flexible and transparent electronics. However, It remains an open question on how to achieve large-scale printing of Ag NWs with high optical transparency, electrical conductivity, and mechanical durability for practical applications, though extensive research has been conducted for more than a decade. In this work, we propose a possible solution that integrates screen printing of Ag NWs with flash-light sintering (FLS). We demonstrate that the use of low-concentration, screen-printable Ag NW ink enables large-area and high-resolution patterning of Ag NWs. A critical advantage comes from the FLS process that allows low-temperature processing, short operational time, and high output rate-characteristics that fit the scalable manufacturing. Importantly, we show that the resultant Ag NW patterns feature low sheet resistance (1.1-9.2 Ohm sq^-1), high transparency (75.2-92.6%), and thus a remarkable figure of merit comparable to state of the art. These outstanding properties of Ag NW patterns, together with the scalable fabrication method we propose, would facilitate many Ag NW-based applications, such as transparent heaters, stretchable displays, and wearable devices; here, we demonstrate the novel design of flexible and transparent radio frequency 5G antennas.

Simple Approach: Heat Treatment to Improve the Electrochemical Performance of Commonly Used Anode Electrodes for Lithium-Ion Batteries

The lithium-ion battery (LIB) industry has been in high demand for simple and effective methods to improve the electrochemical performance of LIBs. Here, we treated three different widely studied anode electrodes (i.e., Li₄Ti₅O₁₂, TiO₂, and graphite) under vacuum at 250 °C, and compared their electrochemical performance with and without a 250 °C treatment. Without changing the composition of the fabricated electrodes, all of the 250 °C treated electrodes exhibited enhanced specific capacities, and the lithium-ion diffusion was improved in different degrees. By comparing the results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy of the pristine and 250 °C treated electrodes, the 250 °C treatment improved the distribution of a polyvinylidene difluoride (PVDF) binder in the electrodes, resulting in a higher porosity of the 250 °C treated electrodes. The results of X-ray photoelectron spectrometry and SEM of the cycled electrodes confirmed that a uniform distribution of the PVDF binder from the 250 °C treatment played a positive role in the formation of a solid electrolyte interphase layer, thereby delivering higher capacities and capacity retentions than those of electrodes without heat treatment. The simplicity of this modification method provides considerable potential for building high-performance LIBs at a larger scale.

Copper(I)-alkylamine mediated synthesis of copper nanowires

Formation of a Cu(i)-alkylamine complex is found to be the key step for Cu(ii) ions to reduce to Cu(0) in the presence of glucose. Also, alkylamines in Cu nanowire synthesis serve triple roles as a reducing, complexation and capping agent. Alkylamines reduce Cu(ii) to Cu(i) at above 100 °C and protect the Cu(i) by forming a Cu ion-alkylamine coordination complex with a 1 : 2 ratio in an aqueous solution. With respect to the 1 : 2 complex ratio, the additional free alkylamines ensure a stable Cu(i)-alkylamine complex. After completion of Cu(i)-Cu(0) reduction by glucose, alkylamines remain on Cu(0) seeds to regulate the anisotropic growth of Cu nanocrystals. Long-chain (≥C16) alkylamines are found to help produce high-quality Cu nanowires, while short-chain (≤C12) alkylamines only produce CuO products. Furthermore, Cu nanowire synthesis is found to be sensitive to additional chemicals as they may destabilize Cu ion-alkylamine complexes. By comparing the Cu(i)-alkylamine and Maillard reaction mediated mechanism, the complete Cu nanowire synthesis process using glucose is revealed.

Programmed Ultrafast Scan Welding of Cu Nanowire Networks with a Pulsed Ultraviolet Laser Beam for Transparent Conductive Electrodes and Flexible Circuits

Metal nanowires (NWs) have shown superior advances for the next-generation transparent conducting (TC) materials. Most concerns were focused on uniform conductive films; however, fabrication of a programmed circuit is still lacking. Here, we demonstrate a programmable ultrafast welding method by pulsed laser beam scanning under ambient conditions to achieve a Cu NW pattern-free TC circuit as well as various size films. High-aspect ratio Cu NWs (> 3000) are synthesized through an oleylamine-mediated solution system. Pulsed ultraviolet laser irradiation together with a programmed moving station is set up for the welding of Cu NW networks. Finite element simulations reveal that the transient heating by efficient absorption of UV light (∼ 250 nm) could remove the organic residues on the surface and realize local welding of interlaced NW junctions. With only 10 ms pulsed irradiation, high optoelectronic performance (33 ohm/sq. at 87% transmittance at 550 nm) and excellent stability of the Cu NW TC film have been achieved. The line-by-line and selected route scanning modes could rapidly make large area TC films and directly write flexible circuits. Moreover, completely transparent micron-size UV and blue LED chips are fabricated and successfully lit with bright emission. This method opens up a future way of circuit and device fabrication by direct one-step laser writing.

Highly efficient and stable transparent electromagnetic interference shielding films based on silver nanowires

Transparent electromagnetic interference (EMI) shielding materials with high optical transmittance and outstanding shielding effectiveness (SE) for optoelectronic devices in visual windows are urgently needed. Herein, we demonstrate the preparation of a transparent EMI shielding film based on silver nanowires (Ag NWs) via a facile Mayer-rod coating method. The electrical conductivity and transmittance of Ag NW-based films can be greatly improved through treatment with NaBH₄ and the lamination of poly(diallyldimethyl-ammonium chloride). The coverage of the polymer decreases the surface roughness, with no damage on the uniform mesh of the Ag NWs. The Ag NW/PDDA composite films present a sheet resistance of 22 Ω sq^-1 at a transmittance of 95.5%, better than that of commercial indium tin oxide (ITO). The excellent optoelectrical performance of the Ag NW/PDDA composite film is further ascertained by fitting the transmittance with the resistance, with a figure of merit of 443. The Ag NW/PDDA composite films in this study exhibit greatly improved stability during 25 °C/65% RH aging for 35 days with the assistance of the coverage layer. Moreover, the EMI SE of the Ag NW/PDDA composite films is 28 dB on average at a transmittance of 91.3%, and continuously increases to 31.3 dB while the optical transmittance is still maintained at 86.8%, which is superior to those of most reported transparent EMI shielding materials. Taken together, the excellent optical transmittance and EMI shielding performance of the Ag NW/PDDA composite film make it an outstanding transparent EMI shielding material in optoelectronic devices, such as aerospace equipment, medical devices, communication facilities, and electronic displays.

Synthesis of Ultrathin Metal Nanowires with Chemically Exfoliated Tungsten Disulfide Nanosheets

Transition metal dichalcogenides (TMDs) have attracted great interest owing to their fascinating properties with atomically thin nature. Although TMDs have been exploited for diverse applications, the effective role of TMDs in the synthesis of metal nanowires has not been explored. Here, we propose a new approach to synthesize ultrathin metal nanowires using TMDs for the first time. High-quality ultrathin nanowires with an average diameter of 11.3 nm are successfully synthesized for realizing high-performance transparent conductors that exhibit excellent conductivity and transparency with low haze. The growth mechanism is carefully investigated using high-resolution transmission electron microscopy, and growth of nanowires with tunable diameters is achieved by controlling the nanosheet dimension. Finally, we unravel the important role of TMDs acting as both reducing and nucleating agents. Therefore, our work provides a new strategy of the TMD as an innovative material for the growth of metal nanowires as a promising building block in next-generation optoelectronics.

Multiscale Soft-Hard Interface Design for Flexible Hybrid Electronics

Emerging next-generation soft electronics will require versatile properties functioning under mechanical compliance, which will involve the use of different types of materials. As a result, control over material interfaces (particularly soft/hard interfaces) has become crucial and is now attracting intensive worldwide research efforts. A series of material and structural interface designs has been devised to improve interfacial adhesion, preventing failure of electromechanical properties under mechanical deformation. Herein, different soft/hard interface design strategies at multiple length scales in the context of flexible hybrid electronics are reviewed. The crucial role of soft ligands and/or polymers in controlling the morphologies of active nanomaterials and stabilizing them is discussed, with a focus on understanding the soft/hard interface at the atomic/molecular scale. Larger nanoscopic and microscopic levels are also discussed, to scrutinize viable intrinsic and extrinsic interfacial designs with the purpose of promoting adhesion, stretchability, and durability. Furthermore, the macroscopic device/human interface as it relates to real-world applications is analyzed. Finally, a perspective on the current challenges and future opportunities in the development of truly seamlessly integrated soft wearable electronic systems is presented.

Tailorable synthesis of heterogeneous enzyme–copper nanobiohybrids and their application in the selective oxidation of benzene to phenol

A new strategy has been developed for the tailor-made synthesis of copper nanoparticle (CuNPs)-enzyme biohybrids in aqueous media for selective benzene monohydroxylation.

Nanowire Genome: A Magic Toolbox for 1D Nanostructures

1D nanomaterials with high aspect ratio, i.e., nanowires and nanotubes, have inspired considerable research interest thanks to the fact that exotic physical and chemical properties emerge as their diameters approach or fall into certain length scales, such as the wavelength of light, the mean free path of phonons, the exciton Bohr radius, the critical size of magnetic domains, and the exciton diffusion length. On the basis of their components, aspect ratio, and properties, there may be imperceptible connections among hundreds of nanowires prepared by different strategies. Inspired by the heredity system in life, a new concept termed the "nanowire genome" is introduced here to clarify the relationships between hundreds of nanowires reported previously. As such, this approach will not only improve the tools incorporating the prior nanowires but also help to precisely synthesize new nanowires and even assist in the prediction on the properties of nanowires. Although the road from start-ups to maturity is long and fraught with challenges, the genetical syntheses of more than 200 kinds of nanostructures stemming from three mother nanowires (Te, Ag, and Cu) are summarized here to demonstrate the nanowire genome as a versatile toolbox. A summary and outlook on future challenges in this field are also presented.

Recent progress of solution-processed Cu nanowires transparent electrodes and their applications

Research on next-generation transparent electrode (TE) materials to replace expensive and fragile indium tin oxide (ITO) is crucial for future electronics. Copper nanowires (Cu NWs) are considered as one of the most promising alternatives due to their excellent electrical properties and low-cost processing. This review summarizes the recent progress on the synthesis methods of long Cu NWs, and the fabrication techniques and protection measures for Cu NW TEs. Applications of Cu NW TEs in electronics, such as solar cells, touch screens, and light emitting diodes (LEDs), are discussed.

Stretchable Transparent Conductors: from Micro/Macromechanics to Applications

Stretchable transparent conductors (STCs), generally consisting of conducting networks and stretchable transparent elastomers, can maintain stable conductivity and transparency even at large tensile strain, beyond the reach of rigid/flexible transparent conductors. They are essential components in stretchable/wearable electronics for using on irregular 3D conformable surfaces and have attracted tremendous attention in recent years. This review aims to provide systematical correlation of the conducting element-substrate interaction with the structural stability of conducting networks, as well as the properties and device applications of STCs. It starts with the micromechanics for stretching of conducting elements on substrates, including the mechanical mismatch, distribution/level of interfacial shear stress, and the deformation behavior of conducting elements on substrates. The macromechanics for stretching of conducting networks on substrates are then further illustrated from a more statistical point of view, namely sliding/preferred orientation of percolation networks, unfolding of buckled structures, and unit cell distortion/distributed rupture of nanomeshes. The structure-dependent properties as well as the state-of-the-art applications of STCs are summarized before ending with the conclusions and outlooks for STCs.

Multifunctional Metallic Nanowires in Advanced Building Applications

Metallic nanowires (NWs) have attracted great attention in the frontiers of nanomaterial science due to their extraordinary properties, such as high thermal and electrical conductivity, high aspect ratio, good mechanical flexibility, and excellent optical transparency. The metallic NWs and their nanocomposites, as a promising alternative for conventional building materials, have been extensively studied recently, but review works on these novel versatile nanostructures and their various uses in the building and construction industry are still lacking. We present a comprehensive review on current state-of-the-art research and progress regarding multifunctional metallic NWs and their specific building applications, including thermal energy storage (TES), thermal transport, electrochromic windows (ECW), as well as photovoltaic (PV) cells. The nanosynthesis techniques and nanocharacterization of silver nanowires (AgNWs) and copper nanowires (CuNWs) are overviewed and compared with each other. In addition, the fundamentals of different NWs for advanced building applications are introduced. Further discussion is presented on the improved performance of base materials by using these nanostructures, highlighting the key factors exhibiting their superior performance. Finally, the key benefits and limitations of metallic NWs for new generation building materials are obtained.

High current carrying and thermal conductive copper-carbon conductors

The surging demand for miniaturized compact devices has generated the need for new metal conductors with high current carrying ampacity, electric and thermal conductivity. Herein, we report carbon-metal conductors that exhibit a high breakdown current density (39% higher than copper) and electrical conductivity (e.g. 63% higher than that of copper at 363 K) in a broad temperature range. The mechanistic studies of thermal conductivity through first-principle modeling show that the multilayer graphene percolation networks efficiently decrease the electron-phonon coupling in the copper-graphene composites, even if phonon modes are activated at a high temperature. These results imply that the copper-based composites have the potential to be the next generation metal conductor with high electrical and thermal conductivity, as well as excellent current-carrying ampacity. More importantly, the developed composite can be deployed in the ink form, making it possible to be utilized by the microelectronic fabrication process.

Flexible Transparent Electrodes Based on Gold Nanomeshes

The transmittance, conductivity, and flexibility are the crucial properties for the development of next-generation flexible electrodes. Achieving a good trade-off between transmittance and conductivity of flexible electrodes has been a challenge because the two properties are inversely proportional. Herein, we reveal a good trade-off between transmittance and conductivity of gold nanomesh (AuNM) can be achieved through appropriately increasing the AuNM thickness no more than 40 nm, the mean free path of electrons in Au metal. The further flexibility investigation indicates that the AuNM electrodes with mesh structure show higher tolerance than the Au bulk film, and the AuNM electrodes with smaller inter-aperture wire width can accommodate more tensile strains than a counterpart with bigger inter-aperture wire width. The simulated results based on finite element analysis (FEA) show good agreement with experimental results, which indicates the fabrication method of versatile nanosphere lithography (NSL) is reliable. These results established a promising approach toward next-generation large-scale flexible transparent AuNM electrodes for flexible electronics.

In Situ Seed-Mediated High-Yield Synthesis of Copper Nanowires on Large Scale

Copper nanowires (Cu NWs) are among ideal candidates for fabricating various advanced nanodevices, especially flexible electronics and transparent conductive electrodes. However, although many efforts have been made, the commercialization of Cu NWs is still difficult. Herein, we report an in situ seed-mediated two-step strategy to synthesize well-defined Cu NWs in high yield. In the first step, that is, seed formation process, most Cu ions (85%) in situ transform to nondecahedral Cu nanodots (NDs). These Cu NDs can promote the formation of decahedral multiply twinned particles (DMTPs) and the subsequent growth of Cu NWs by selectively inhibiting the spontaneous ripening of nanoparticle (NP) byproducts in the second step. The amount and quality of Cu NDs play an important role in high-yield production of Cu NWs, and the yield was successfully increased to 2.4 times higher than that of the conventional methods. Furthermore, an effective shaking-rotating purification technique was developed to fully separate Cu NWs from the final product solution. After scaling up the reaction, 50 g of high-quality Cu NWs can be produced with a uniform size and high aspect ratio at a very low material cost of $ 0.99/g. These promising results not only provide a high-yield and low-cost synthetic route but also can promote the widespread commercialization of Cu NWs in advanced nanodevices.

Synthesis and modelling of the mechanical properties of Ag, Au and Cu nanowires

The recent interest to nanotechnology aims not only at device miniaturisation, but also at understanding the effects of quantised structure in materials of reduced dimensions, which exhibit different properties from their bulk counterparts. In particular, quantised metal nanowires made of silver, gold or copper have attracted much attention owing to their unique intrinsic and extrinsic length-dependent mechanical properties. Here we review the current state of art and developments in these nanowires from synthesis to mechanical properties, which make them leading contenders for next-generation nanoelectromechanical systems. We also present theories of interatomic interaction in metallic nanowires, as well as challenges in their synthesis and simulation.