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.

Reliable fabrication of micro/nanostructures with sub-10 nm features is of great significance for advancing nanoscience and nanotechnology. While the capability of current complementary metal-oxide semiconductor (CMOS) chip manufacturing can produce structures on the sub-10 nm scale, many emerging applications, such as nano-optics, biosensing, and quantum devices, also require ultrasmall features down to single digital nanometers. In these emerging applications, CMOS-based manufacturing methods are currently not feasible or appropriate due to the considerations of usage cost, material compatibility, and exotic features. Therefore, several specific methods have been developed in the past decades for different applications. In this review, we attempt to give a systematic summary on sub-10 nm fabrication methods and their related applications. In the first and second parts, we give a brief introduction of the background of this research topic and explain why sub-10 nm fabrication is interesting from both scientific and technological perspectives. In the third part, we comprehensively summarize the fabrication methods and classify them into three main approaches, including lithographic, mechanics-enabled, and post-trimming processes. The fourth part discusses the applications of these processes in quantum devices, nano-optics, and high-performance sensing. Finally, a perspective is given to discuss the challenges and opportunities associated with this research topic.

many irreplaceable advantages of high storage capacity, miniaturization, multi plicity, and integration capability. [6][7][8][9][10][11] Among various microoptics/nano optics devices, metasurface, consisting of planar subwavelength structures, has emerged as a particularly powerful plat form for modulating light parameters such as amplitude, [12,13] phase, [14][15][16] wavelength, [17][18][19][20] polarization, [4,[21][22][23] and hybrid parameters, [24,25] which provides the possibility of potential applications of information encryption, data storage, and optical communication. [26][27][28] Microprint and holography are often used as two separate optical encryption strategies applied in independent meta surface devices, which can be achieved by controlling over plasmonic [29][30][31][32][33][34] or all dielectric [35][36][37][38][39][40] structures at the nanoscale. To strengthen optical information secu rity, other parametric freedoms such as polarization, [41][42][43][44][45] wavelength, [17,[46][47][48][49] and spatial freedom [50][51][52] have been explored to achieve multiplexed microprint or holography encryption devices. Very recently, attempts have been imple mented to combine the microprint and holography in a single device. [53][54][55] However, although the combination of holography and microprints brings about the increase of encrypted dimen sions, crosstalk between different channels remains a thorny problem, and devices will not transmit repeatedly between senders and receivers once fabricated. Fabry-Pérot (FP) cavity resonators with narrow spectral linewidth can effectively sup press crosstalk and can be integrated to act as color filters, [56,57] which provides a potential solution. However, significant chal lenges such as realtime encryption, transmission security, and data compactness still need to be overcome.Here, we propose a novel type of metasurfacebased device that combines color FP cavitybased microprint and helicity multiplexed metahologram. Such devices have the encryption dimensions of microprint, holography as well as helicity at the same time by independently manipulating the amplitude, phase, and polarization of the incident light. A specific algo rithmic framework is developed to combine holography with structural color, and the particle swarm optimization (PSO) algorithm is built to optimize the conversion efficiencies of metasurface elements. Furthermore, enabled by a microprint of editable quick response (QR) code, a realtime encryption Optical encryption with multichannel, high complexity, and artistry characteristics has become one of the most significant approaches for modern information security. Recently emerged metasurface-based optics consisting of planar subwavelength metamaterials has been engineered as an ideal platform for optical encryption because of its capability of manipulating various optical parameters and enhancing information storage capacity. However, limited encrypted channels and insufficient real-time encryption abilities hinder its practical applicatio...

Growth of large-area, uniform, and high-quality monolayer transition-metal dichalcogenides (TMDs) for practical and industrial applications remains a long-standing challenge. The present study demonstrates a modified predeposited chemical vapor deposition (CVD) process by employing an annealing procedure before sulfurization, which helps in achieving large-area, highly uniform, and high-quality TMDs on various substrates. The annealing procedure resulted in a molten liquid state of the precursors in the CVD process, which not only facilitated a uniform redistribution of the precursor on the substrate (avoid the aggregation) because of the uniform redistribution of the liquid precursor on the substrate but more importantly avoided the undesired multilayer growth via the selflimited lateral supply precursors mechanism. A 2 in. uniform and continuous monolayer WS 2 film has been synthesized on the SiO 2 /Si substrate. Moreover, uniform monolayer WS 2 single crystals can be prepared on more general and various substrates including sapphire, mica, quartz, and Si 3 N 4 using the same growth procedure. Besides, this growth mechanism can be generalized to synthesize other monolayer TMDs such as MoS 2 and MoS 2 /WS 2 heterostructures. Hence, the present method provides a generalized attractive strategy to grow large-area, uniform, single-layer two-dimensional (2D) materials. This study has significant implications in the advancement of batch production of various 2D-material-based devices for industrial and commercial applications.

Polarization is a common and unique phenomenon in nature, which reveals more camouflage features of object. However, current polarization-perceptual devices based on conventional physical architectures are still facing enormous challenges...