High-resolution multicolor printing based on pixelated optical nanostructures is of great importance for promoting advances in color display science. So far, most of the work in this field has been ...focused on achieving static colors, limiting many potential applications. This inevitably calls for the development of dynamic color displays with advanced and innovative functionalities. In this Letter, we demonstrate a novel dynamic color printing scheme using magnesium-based pixelated Fabry-Pérot cavities by gray scale nanolithography. With controlled hydrogenation and dehydrogenation, magnesium undergoes unique metal and dielectric transitions, enabling distinct blank and color states from the pixelated Fabry-Pérot resonators. Following such a scheme, we first demonstrate dynamic Ishihara plates, in which the encrypted images can only be read out using hydrogen as information decoding key. We also demonstrate a new type of dynamic color generation, which enables fascinating transformations between black/white printing and color printing with fine tonal tuning. Our work will find wide-ranging applications in full-color printing and displays, colorimetric sensing, information encryption and anticounterfeiting.
The exact role of a defect structure on transition metal compounds for electrocatalytic oxygen evolution reaction (OER), which is a very dynamic process, remains unclear. Studying the ...structure–activity relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction mechanism and dynamic behavior of defect sites. Co3O4 with rich oxygen vacancy (VO) has been reported to efficiently catalyze OER. Herein, we constructed pure spinel Co3O4 and VO-rich Co3O4 as catalyst models to study the defect mechanism and investigate the dynamic behavior of defect sites during the electrocatalytic OER process by various operando characterizations. Operando electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) implied that the VO could facilitate the pre-oxidation of the low-valence Co (Co2+, part of which was induced by the VO to balance the charge) at a relatively lower applied potential. This observation confirmed that the VO could initialize the surface reconstruction of VO–Co3O4 prior to the occurrence of the OER process. The quasi-operando X-ray photoelectron spectroscopy (XPS) and operando X-ray absorption fine structure (XAFS) results further demonstrated the oxygen vacancies were filled with OH• first for VO–Co3O4 and facilitated pre-oxidation of low-valence Co and promoted reconstruction/deprotonation of intermediate Co–OOH•. This work provides insight into the defect mechanism in Co3O4 for OER in a dynamic way by observing the surface dynamic evolution process of defective electrocatalysts and identifying the real active sites during the electrocatalysis process. The current finding would motivate the community to focus more on the dynamic behavior of defect electrocatalysts.
MOF‐derived ZnO@ZnO Quantum Dots/C core–shell nanorod arrays grown on flexible carbon cloth are successfully fabricated as a binder‐free anode for Li‐ion storage. In combination with the advantages ...from the ZnO/C core–shell architecture and the 3D nanorod arrays, this material satisfies both efficient ion and fast electron transport, and thus shows superior rate capability and excellent cycling stability.
Lightweight, miniaturized optical imaging systems are vastly anticipated in these fields of aerospace exploration, industrial vision, consumer electronics, and medical imaging. However, conventional ...optical techniques are intricate to downscale as refractive lenses mostly rely on phase accumulation. Metalens, composed of subwavelength nanostructures that locally control light waves, offers a disruptive path for small-scale imaging systems. Recent advances in the design and nanofabrication of dielectric metalenses have led to some high-performance practical optical systems. This review outlines the exciting developments in the aforementioned area whilst highlighting the challenges of using dielectric metalenses to replace conventional optics in miniature optical systems. After a brief introduction to the fundamental physics of dielectric metalenses, the progress and challenges in terms of the typical performances are introduced. The supplementary discussion on the common challenges hindering further development is also presented, including the limitations of the conventional design methods, difficulties in scaling up, and device integration. Furthermore, the potential approaches to address the existing challenges are also deliberated.
The electrochemical nitrogen fixation under mild conditions is a promising alternative to the current nitrogen industry with high energy consumption and greenhouse gas emission. Here, a nanoporous ...boron carbide (np‐B13C2) catalyst is reported for electrochemical nitrogen fixation, which is fabricated by the combination of metallurgical alloy design and chemical etching. The resulting np‐B13C2 exhibits versatile catalytic activities towards N2 reduction reactions (NRR) and N2 oxidation reaction (NOR). A high NH3 yield of 91.28 µg h−1 mgcat.−1 and Faradaic efficiency (FE) of 35.53% at −0.05 V versus the reversible hydrogen electrode are obtained for NRR, as well as long‐term stability of up to 70 h, making them among the most active NRR electrocatalysts. This catalyst can also achieve a NO3− yield of 165.8 µg h−1 mgcat.−1 and a FE of 8.4% for NOR. In situ Raman spectroscopy and density functional theory calculations reveal that strong coupling between the BC sites modulates the electronic structures of adjacent B atoms of B13C2, which enables the B sites to effectively adsorb and activate chemical inert N2 molecules, resulting in lowered energy required by the potential‐determining step. Besides, the introduction of carbon can increase the inherent conductivity and reduce the binding energy of the reactants, thus improving N2 fixation performance.
A nanoporous B13C2 is fabricated by metallurgical alloy design and chemical etching approach, which can achieve high selectivity and excellent stability towards both NRR and NOR. The strong interaction between BC sites modulates the electronic structures of adjacent B atoms, which enables the B sites to effectively stabilize the transition state and lower the barrier for improving N2 fixation performance.
A novel and scalable synthesis approach to produce hierarchically aligned porous carbon nanotube arrays (PCNTAs) on flexible carbon fibers (CFs) is developed. The PCNTAs are obtained by catalytic ...conversion of ethanol on ZnO nanorod arrays and then reduction‐evaporation of ZnO nanorods, resulting in uniform and controllable wall thicknesses of the final PCNTAs. The 3D arrangement, the diameters, and the lengths of the PCNTAs can be tuned by adjusting the synthesis protocols of the ZnO nanorod arrays. The PCNTAs@CFs exhibit a high specific capacitance of 182 F g−1 at 40 A g−1 (188 F g−1 at 20 A g−1) in 6 m KOH. The symmetric supercapacitor shows an excellent cycling stability with only 0.0016% loss per cycle after 10 000 continuous cycles at the current density of 12 A g−1. These excellent electrochemical performances are ascribed to the unique structural design of hierarchical PCNTAs, which provide not only appropriate channels for enhanced electronic and ionic transport but also increased surface area for accessing more electrolyte ions. The structural design and the synthesis approach are general and can be extended to synthesizing a broad range of materials systems.
Radially aligned porous carbon nanotube arrays with desired mesopores and intimate contact with carbon fibers substrate facilitate fast transport of both electrons and electrolyte ions to provide high rate capability at high current density. Such unique hierarchical nanoarchitectures demonstrate excellent cycling stability and good mechanical properties, making them more applicable in flexible energy storage devices.
Metamaterials with artificial optical properties have attracted significant research interest. In particular, artificial magnetic resonances with non-unity permeability tensor at optical frequencies ...in metamaterials have been reported. However, only non-unity diagonal elements of the permeability tensor have been demonstrated to date. A gyromagnetic permeability tensor with non-zero off-diagonal elements has not been observed at the optical frequencies. Here we report the observation of gyromagnetic properties in the near-infrared wavelength range in a magneto-plasmonic metamaterial. The non-zero off-diagonal permeability tensor element causes the transverse magneto-optical Kerr effect under s-polarized incidence that otherwise vanishes if the permeability tensor is not gyromagnetic. By retrieving the permeability tensor elements from reflection, transmission, and transverse magneto-optical Kerr effect spectra, we show that the effective off-diagonal permeability tensor elements reach 10
level at the resonance wavelength (~900 nm) of the split-ring resonators, which is at least two orders of magnitude higher than magneto-optical materials at the same wavelength. The artificial gyromagnetic permeability is attributed to the change in the local electric field direction modulated by the split-ring resonators. Our study demonstrates the possibility of engineering the permeability and permittivity tensors in metamaterials at arbitrary frequencies, thereby promising a variety of applications of next-generation nonreciprocal photonic devices, magneto-plasmonic sensors, and active metamaterials.
Abstract
Glasses-free three-dimensional (3D) displays are one of the game-changing technologies that will redefine the display industry in portable electronic devices. However, because of the limited ...resolution in state-of-the-art display panels, current 3D displays suffer from a critical trade-off among the spatial resolution, angular resolution, and viewing angle. Inspired by the so-called spatially variant resolution imaging found in vertebrate eyes, we propose 3D display with spatially variant information density. Stereoscopic experiences with smooth motion parallax are maintained at the central view, while the viewing angle is enlarged at the periphery view. It is enabled by a large-scale 2D-metagrating complex to manipulate dot/linear/rectangular hybrid shaped views. Furthermore, a video rate full-color 3D display with an unprecedented 160° horizontal viewing angle is demonstrated. With thin and light form factors, the proposed 3D system can be integrated with off-the-shelf purchased flat panels, making it promising for applications in portable electronics.
The rapid progress of micro/nanoelectronic systems and miniaturized portable devices has tremendously increased the urgent demands for miniaturized and integrated power supplies. Miniaturized energy ...storage devices (MESDs), with their excellent properties and additional intelligent functions, are considered to be the preferable energy supplies for uninterrupted powering of microsystems. In this review, we aim to provide a comprehensive overview of the background, fundamentals, device configurations, manufacturing processes, and typical applications of MESDs, including their recent advances. Particular attention is paid to advanced device configurations, such as two-dimensional (2D) stacked, 2D planar interdigital, 2D arbitrary-shaped, three-dimensional planar, and wire-shaped structures, and their corresponding manufacturing strategies, such as printing, scribing, and masking techniques. Additionally, recent developments in MESDs, including microbatteries and microsupercapacitors, as well as microhybrid metal ion capacitors, are systematically summarized. A series of on-chip microsystems, created by integrating functional MESDs, are also highlighted. Finally, the remaining challenges and future research scope on MESDs are discussed.
Replacing electrons with photons is a compelling route toward high-speed, massively parallel, and low-power artificial intelligence computing. Recently, diffractive networks composed of phase ...surfaces were trained to perform machine learning tasks through linear optical transformations. However, the existing architectures often comprise bulky components and, most critically, they cannot mimic the human brain for multitasking. Here, we demonstrate a multi-skilled diffractive neural network based on a metasurface device, which can perform on-chip multi-channel sensing and multitasking in the visible. The polarization multiplexing scheme of the subwavelength nanostructures is applied to construct a multi-channel classifier framework for simultaneous recognition of digital and fashionable items. The areal density of the artificial neurons can reach up to 6.25 × 10
mm
multiplied by the number of channels. The metasurface is integrated with the mature complementary metal-oxide semiconductor imaging sensor, providing a chip-scale architecture to process information directly at physical layers for energy-efficient and ultra-fast image processing in machine vision, autonomous driving, and precision medicine.
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