High‐Resolution Patterning of Various Large‐Area,Highly Ordered Structural Motifs by Directional Photofluidization Lithography: Sub‐30‐nm Line,Ellipsoid, Rectangle,and Circle Arrays

A major challenge in nanolithography is to overcome the resolution limit of conventional patterning methods. Herein, we demonstrate a simple and convenient approach to generate sub‐30‐nm various structural motifs with precisely controlled sizes, shapes, and orientations. The proposed method, the “directional photofluidization” of an azopolymer, follows the same philosophy as a path‐changing approach, for example, thermal‐reflow of polymer arrays, in that post‐treatment simultaneously leads to a reduction of the feature sizes and line‐edge roughness (LER) of nanostructures. However, in contrast to thermal‐induced isotropic reflow, directional photofluidization provides unprecedented flexibility to control the structural features, because the direction of photofluidization can be arbitrary controlled according to the light polarization. Furthermore, this approach offers good control of the final features due to a gradual reduction in the rate of photofluidization during light irradiation. More importantly, the photofluidic behavior of the azopolymer significantly reduces the LER, and thus it can improve the quality of nanostructures. Finally, the far‐field process of directional photofluidization enables hierarchical nanofabrication, in contrast to mechanical contact fabrication, because the patterned light can reconfigure the polymer arrays selectively. Our approach is potentially advantageous for the fabrication of various structural motifs with well‐controlled dimensions on the nanoscale and with minimized LER.     

Simple Holographic Patterning for High‐Aspect‐Ratio Three‐Dimensional Nanostructures with Large Coverage Area

Using the vertical standing wave phenomena commonly regarded as a deterrent in holographic lithography, multifaceted three‐dimensional (3D) nanostructures are fabricated on polymeric photoresist materials using a simple two‐beam interferometer. Large‐area 3D nanostructures with high aspect ratios (greater than 10) are readily produced using this methodology, including grating, pillar and pore patterns. Furthermore, manipulation of the lithography process conditions results in unique sidewall profiles of the nanostructures. Such 3D holographic control even produces highly porous polymer membranes composed of 3D interconnected pore networks, which resembles the 3D photonic crystal compound nanostructures that were previously attainable only with limited pattern coverage area using complex multibeam holographic lithography processes. Such well‐tailored high‐aspect‐ratio 3D nanostructures with large pattern coverage area further enable the fabrication of novel nanostructures for functionalized materials via various additive and subtractive pattern transfer techniques such as etching, deposition, and molding. In particular, direct molding followed by thermal decomposition process leads to the synthesis of hierarchical titanium oxide nanostructures of tunable 3D geometry, which would be of great significance in applications of photonic crystals, photovoltaic solar cells, and photocatalyst in water decontamination.     

Autogenous Growth of Hierarchical NiFe(OH)x/FeS Nanosheet‐On‐Microsheet Arrays for Synergistically Enhanced High‐Output Water Oxidation

Practical electrochemical water splitting requires cost‐effective electrodes capable of steadily working at high output, leading to the challenges for efficient and stable electrodes for the oxygen evolution reaction (OER). Herein, by simply using conductive FeS microsheet arrays vertically pre‐grown on iron foam (FeS/IF) as both substrate and source to in situ form vertically aligned NiFe(OH)_x nanosheets arrays, a hierarchical electrode with a nano/micro sheet‐on‐sheet structure (NiFe(OH)_x/FeS/IF) can be readily achieved to meet the requirements. Such hierarchical electrode architecture with a superhydrophilic surface also allows for prompt gas release even at high output. As a result, NiFe(OH)_x/FeS/IF exhibits superior OER activity with an overpotential of 245 mV at 50 mA cm^?2 and can steadily output 1000 mA cm^?2 at a low overpotential of 332 mV. The water‐alkali electrolyzer using NiFe(OH)_x/FeS/IF as the anode can deliver 10 mA cm^?2 at 1.50 V and steadily operate at 300 mA cm^?2 with a small cell voltage for 70 h. Furthermore, a solar‐driven electrolyzer using the developed electrode demonstrates an exceptionally high solar‐to‐hydrogen efficiency of 18.6%. Such performance together with low‐cost Fe‐based materials and facile mass production suggest the present strategy may open up opportunities for rationally designing hierarchical electrocatalysts for practical water splitting or diverse applications.     

In Situ Fabrication of Three‐Dimensional Graphene Films on Gold Substrates with Controllable Pore Structures for High‐Performance Electrochemical Sensing

In this work, novel three‐dimensional graphene films (3D GFs) with controllable pore structures are directly fabricated on gold substrates through the hydrothermal reduction. An interfacial technique of the self‐assembled monolayer is successfully introduced to address the binding issue between the graphene film and substrate. Adscititious silica spheres, serving as new connection centers, effectively regulate the dimensions of framework in graphene films, and secondary pore structures are produced once removing the spheres. Based on hierarchically porous 3D GFs with large surface area, excellent binding strength, high conductivity, and distinct interfacial micro‐environments, selected examples of electrochemical aptasensors are constructed for the assay of adenosine triphosphate (ATP) and thrombin (Tob) respectively. Sensitive ATP and Tob aptasensors, with high selectivity, excellent stability, and promising potential in real serum sample analysis, are established on 3D GFs with different structures. The results demonstrate that the surface area, as well as interfacial micro‐environments, plays a critical role in the molecular recognition. The developed reliable and scalable protocol is envisaged to become a general path for in situ fabrication of more graphene films and the as‐synthesized 3D GFs would open up a wide horizon for potential applications in electronic and energy‐related systems.     

Engineering Hierarchical Hollow Nickel Sulfide Spheres for High‐Performance Sodium Storage

Sodium‐ion batteries (SIBs) are considered as promising alternatives to lithium‐ion batteries (LIBs) for energy storage due to the abundance of sodium, especially for grid distribution systems. The practical implementation of SIBs, however, is severely hindered by their low energy density and poor cycling stability due to the poor electrochemical performance of the existing electrodes. Here, to achieve high‐capacity and durable sodium storage with good rate capability, hierarchical hollow NiS spheres with porous shells composed of nanoparticles are designed and synthesized by tuning the reaction parameters. The formation mechanism of this unique structure is systematically investigated, which is clearly revealed to be Ostwald ripening mechanism on the basis of the time‐dependent morphology evolution. The hierarchical hollow structure provides sufficient electrode/electrolyte contact, shortened Na⁺ diffusion pathways, and high strain‐tolerance capability. The hollow NiS spheres deliver high reversible capacity (683.8 mAh g^?1 at 0.1 A g^?1), excellent rate capability (337.4 mAh g^?1 at 5 A g^?1), and good cycling stability (499.9 mAh g^?1 with 73% retention after 50 cycles at 0.1 A g^?1).     

Bioinspired Assembly of Hierarchical Light‐Harvesting Architectures for Improved Photophosphorylation

Molecular assembly offers a bottom‐up way to construct biomimetic architectures with unique structures and properties. Although artificial photophosphorylation systems have long been developed, their microstructures have yet to achieve the sophisticated order and hierarchy of natural organisms. Herein, by utilizing principles in the natural plant leaves, it is shown that a biomimetic system with hierarchically ordered and compartmentalized structures, combining photosystem II (PSII) and adenosine triphosphate (ATP) synthase, can be obtained through template‐directed layer‐by‐layer assembly. Under light illumination, PSII in such a highly ordered light‐harvesting array, splits water to produce protons and electrons. Furthermore, a remarkable proton gradient is created across the covering ATP synthase‐reconstituted lipid membrane. As a consequence, highly efficient photophosphorylation is achieved. Outstandingly, the rate of ATP production in this hierarchical light‐harvesting architecture is enhanced 14 times, compared to that in the nature. This study paves a new way to assemble bioinspired systems with enhanced solar‐to‐chemical energy conversion efficiency.     

Conductive Hierarchical Hairy Fibers for Highly Sensitive,Stretchable, and Water‐Resistant Multimodal Gesture‐Distinguishable Sensor,VR Applications

Conductive fibers, which are highly adaptable to the morphologies of the human body, are attractive for the development of wearable systems, smart clothing, and textronics to detect various biological signals and human motions. A fiber‐based conductive sensor interconnected with hierarchical microhairy architectures, exhibiting remarkable stretchability (<200%) and sensitivity for various stimuli (pressure, stretching, and bending), is developed. For distinguishability of multiple gestures, two hierarchical hairy conductive fibers are twisted to fabricate a fiber‐type sensor, which monitors distinct waveforms of electrical signals retrieved from pressure, stretching, and bending. This sensor is highly robust under repeated appliances of external stimuli over multiple cyclic tests of various modes (<2200 cycles for each stimulus). Upon formation of a self‐assembled monolayer, it exhibits stable performance even under wet conditions. For practical applications, this sensor can be weaved into a smart glove to demonstrate a pressure and gesture‐discernible wearable controller for virtual reality (VR) interface, shedding light on advances in wearable electronics with medical and healthcare functionalities and VR systems.     

Fully High‐Temperature‐Processed SnO2 as Blocking Layer and Scaffold for Efficient,Stable, and Hysteresis‐Free Mesoporous Perovskite Solar Cells

Planar perovskite solar cells (PSCs) based on low‐temperature‐processed (LTP) SnO₂ have demonstrated excellent photovoltaic properties duo to the high electron mobility, wide bandgap, and suitable band energy alignment of LTP SnO₂. However, planar PSCs or mesoporous (mp) PSCs based on high‐temperature‐processed (HTP) SnO₂ show much degraded performance. Here, a new strategy with fully HTP Mg‐doped quantum dot SnO₂ as blocking layer (bl) and a quite thin SnO₂ nanoparticle as mp layer are developed. The performances of both planar and mp PSCs has been greatly improved. The use of Mg‐SnO₂ in planar PSCs yields a high‐stabilized power conversion efficiency (PCE) of close to 17%. The champion of mp cells exhibits hysteresis free and stable performance with a high‐stabilized PCE of 19.12%. The inclusion of thin mp SnO₂ in PSCs not only plays a role of an energy bridge, facilitating electrons transfer from perovskite to SnO₂ bl, but also enhances the contact area of SnO₂ with perovskite absorber. Impedance analysis suggests that the thin mp layer is an “active scaffold” selectively collecting electrons from perovskite and can eliminate hysteresis and effectively suppress recombination. This is an inspiring advance toward high‐performance PSCs with HTP mp SnO₂.     

An Epoxy Photoresist Modified by Luminescent Nanocrystals for the Fabrication of 3D High‐Aspect‐Ratio Microstructures

An epoxy‐based negative‐tone photoresist, which is known as a suitable material for high‐aspect‐ratio surface micromachining, is functionalized with red‐light‐emitting CdSe@ZnS nanocrystals (NCs). The proper selection of a common solvent for the NCs and the resist is found to be critical for the efficient incorporation of the NCs in the epoxy matrix. The NC‐modified resist can be patterned by standard UV lithography down to micrometer‐scale resolution, and high‐aspect‐ratio structures have been successfully fabricated on a 100 mm scaled wafer. The “as‐fabricated”, 3D, epoxy‐based surface microstructures show the characteristic luminescent properties of the embedded NCs, as verified by fluorescence microscopy. This issue demonstrates that the NC emission properties can be conveniently conveyed into the polymer matrix without deteriorating the lithographic performance of the latter. The dimensions, the resolution, and the surface morphology of the NC‐modified‐epoxy microstructures exhibit only minor deviations with respect to that of the unmodified reference material, as examined by means of microscopic and metrologic investigations. The proposed approach of the incorporation of emitting and non‐bleachable NCs into a photoresist opens novel routes for surface patterning of integrated microsystems with inherent photonic functionality at the micro‐ and nanometer‐scale for light sensing and emitting applications.     

Solution‐Processed,Alkali Metal‐Salt‐Doped,Electron‐Transport Layers for High‐Performance Phosphorescent Organic Light‐Emitting Diodes

High‐performance, blue, phosphorescent organic light‐emitting diodes (PhOLEDs) are achieved by orthogonal solution‐processing of small‐molecule electron‐transport material doped with an alkali metal salt, including cesium carbonate (Cs₂CO₃) or lithium carbonate (Li₂CO₃). Blue PhOLEDs with solution‐processed 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) electron‐transport layer (ETL) doped with Cs₂CO₃ show a luminous efficiency (LE) of 35.1 cd A^?1 with an external quantum efficiency (EQE) of 17.9%, which are two‐fold higher efficiency than a BPhen ETL without a dopant. These solution‐processed blue PhOLEDs are much superior compared to devices with vacuum‐deposited BPhen ETL/alkali metal salt cathode interfacial layer. Blue PhOLEDs with solution‐processed 1,3,5‐tris(m‐pyrid‐3‐yl‐phenyl)benzene (TmPyPB) ETL doped with Cs₂CO₃ have a luminous efficiency of 37.7 cd A^?1 with an EQE of 19.0%, which is the best performance observed to date in all‐solution‐processed blue PhOLEDs. The results show that a small‐molecule ETL doped with alkali metal salt can be realized by solution‐processing to enhance overall device performance. The solution‐processed metal salt‐doped ETLs exhibit a unique rough surface morphology that facilitates enhanced charge‐injection and transport in the devices. These results demonstrate that orthogonal solution‐processing of metal salt‐doped electron‐transport materials is a promising strategy for applications in various solution‐processed multilayered organic electronic devices.     

Graphene Oxide Gel‐Derived,Free‐Standing,Hierarchically Porous Carbon for High‐Capacity and High‐Rate Rechargeable Li‐O2 Batteries

Lithium‐oxygen (Li‐O₂) batteries are one of the most promising candidates for high‐energy‐density storage systems. However, the low utilization of porous carbon and the inefficient transport of reactants in the cathode limit terribly the practical capacity and, in particular, the rate capability of state‐of‐the‐art Li‐O₂ batteries. Here, free‐standing, hierarchically porous carbon (FHPC) derived from graphene oxide (GO) gel in nickel foam without any additional binder is synthesized by a facile and effective in situ sol‐gel method, wherein the GO not only acts as a special carbon source, but also provides the framework of a 3D gel; more importantly, the proper acidity via its intrinsic COOH groups guarantees the formation of the whole structure. Interestingly, when employed as a cathode for Li‐O₂ batteries, the capacity reaches 11 060 mA h g^?1 at a current density of 0.2 mA cm^?2 (280 mA g^?1); and, unexpectedly, a high capacity of 2020 mA h g^?1 can be obtained even the current density increases ten times, up to 2 mA cm^?2 (2.8 A g^?1), which is the best rate performance for Li‐O₂ batteries reported to date. This excellent performance is attributed to the synergistic effect of the loose packing of the carbon, the hierarchical porous structure, and the high electronic conductivity of the Ni foam.     

Reliable Patterning,Transfer Printing and Post‐Assembly of Multiscale Adhesion‐Free Metallic Structures for Nanogap Device Applications

Patterning of metallic nanogaps with ultrasmall gap size on arbitrary substrates is of great importance for various applications in nanoelectronics, nanoplasmonics, and flexible optoelectronics. Common lithographic approaches suffer from limited resolution in defining ultrasmall nanogaps and restrictive available substrates for flexible and stretchable devices. In this work, a process portfolio to overcome the above limitations is proposed, enabling the fabrication of multiscale metallic nanogaps with reduced gap size on specific substrates for functional devices. The portfolio combines the recently developed sketch and peel lithography strategy, nanotransfer printing, and post‐mechanical assembly. Among the portfolio, the sketch and peel lithography strategy provides the unique capability to rapidly and reliably define multiscale adhesion‐free metallic nanostructures and nanogaps, which significantly facilitates the subsequent transfer printing process. Nanoplasmonic and nanoelectronic devices with ultrasmall nanogaps that are inaccessible with existing patterning approaches are fabricated to demonstrate the applicability of this fabrication strategy. The portfolio could also have potential for a variety of other applications in flexible and stretchable optics, electronics, and optoelectronics.     

Bio‐Inspired Nanospiky Metal Particles Enable Thin,Flexible, and Thermo‐Responsive Polymer Nanocomposites for Thermal Regulation

Safety issues remain a major obstacle toward large‐scale applications of high‐energy lithium‐ion batteries. Embedding thermo‐responsive polymer switching materials (TRPS) into batteries is a potential strategy to prevent thermal runaway, which is a major cause of battery failures. Here, thin, flexible, highly responsive polymer nanocomposites enabled by bio‐inspired nanospiky metal (Ni) particles are reported. These unique Ni particles are synthesized by a simple aqueous reaction at gram‐scale with controlled surface morphology and composition to optimize electrical properties of the nanocomposites. The Ni particles provide TRPS films with a high room‐temperature conductivity of up to 300 S cm^?1. Such TRPS composite films also have a high rate (<1 s) of resistance switching within a narrow temperature range, good reversibility upon on/off switching, and a tunable switching temperature (T_s; 75 to 170 °C) that can be achieved by tailing their compositions. The small size (≈500 nm) of Ni particles enables ready fabrication of thin and flexible TPRS films with thickness approaching 5 µm or less. These features suggest the great potential of using this new type of responsive polymer composite for more effective battery thermal regulation without sacrificing cell performance.     

High‐Performance,Low‐Cost,and Dense‐Structure Electrodes with High Mass Loading for Lithium‐Ion Batteries

Lithium‐ion batteries have undergone a remarkable development in the past 30 years. However, conventional electrodes are insufficient for the ever‐increasing demand of high‐energy batteries. Here, reported is a thick electrode with a dense structure, as an alternative to the commonly recognized porous framework. A low‐temperature sintering technology with the aid of aqueous solvent, high pressure, and an ion‐conductive additive is originally developed for preparing the LiCoO₂ (LCO)/Li₄Ti₅O₁₂ (LTO) dense‐structure electrode as the representative cathode/anode material. The 400 µm thick cathode with 110 mg cm^?2 mass loading achieves a high specific capacity of 131.2 mAh g^?1 with a good capacity retention of 96% over 150 cycles, far exceeding the commercial counterpart (≈40 µm) of 54.1 mAh g^?1 with 39%. The ultrathick electrode of 1300 µm thickness presents a remarkable area capacity of 28.6 mAh cm^?2 that is 16 times that of the commercial electrode. The full cell based on the dense electrodes delivers an extremely high areal capacity of 14.4 mAh cm^?2. The ion‐diffusion coefficients of the densely sintered electrodes increase by nearly three orders of magnitude. This design opens up a new avenue for scalable and sustainable material manufacturing towards various practical applications.     

Fe3C‐Co Nanoparticles Encapsulated in a Hierarchical Structure of N‐Doped Carbon as a Multifunctional Electrocatalyst for ORR,OER, and HER

Rational design of non‐noble metal catalysts with robust and durable electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is extremely important for renewable energy conversion and storage, regenerative fuel cells, rechargeable metal–air batteries, water splitting etc. In this work, a unique hybrid material consisting of Fe₃C and Co nanoparticles encapsulated in a nanoporous hierarchical structure of N‐doped carbon (Fe₃C‐Co/NC) is fabricated for the first time via a facile template‐removal method. Such an ingenious structure shows great features: the marriage of 1D carbon nanotubes and 2D carbon nanosheets, abundant active sites resulting from various active species of Fe₃C, Co, and NC, mesoporous carbon structure, and intimate integration among Fe₃C, Co, and NC. As a multifunctional electrocatalyst, the Fe₃C‐Co/NC hybrid exhibits excellent performance for ORR, OER, and HER, outperforming most of reported triple functional electrocatalysts. This study provides a new perspective to construct multifunctional catalysts with well‐designed structure and superior performance for clean energy conversion technologies.     

Hierarchical Porous Ni3S4 with Enriched High‐Valence Ni Sites as a Robust Electrocatalyst for Efficient Oxygen Evolution Reaction

Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni₃S₄ architecture, enriched in Ni³⁺ is designed as an advanced electrocatalyst for OER. The obtained Ni₃S₄ architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm^?2 and 300 mV at 50 mA cm^?2. Additionally, this Ni₃S₄ catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm^?2). The outstanding OER performance is due to the high concentration of Ni³⁺ and the meso–macro hierarchical porous structure. The presence of Ni³⁺ enhances the chemisorption of OH^?, which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni₃S₄ as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm^?2. Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni³⁺ and hierarchical porous architectures.