Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer. Wafer-scale uniformity of hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, and molybdenum diselenide monolayers was verified by photoluminescence response and by substantial retention of electronic conductivity. We fabricated wafer-scale van der Waals heterostructures, including field-effect transistors, with single-atom thickness resolution.

Given their low cost and eco-friendliness, rechargeable Zn-ion batteries (ZIBs) have received increasing attention as a device with great potential for large-scale energy storage. However, the development of ZIBs with high capacities and long lifespans is challenging because of the dendritic growth of Zn and the absence of suitable cathode materials. Herein, we report a novel rechargeable aqueous Zn-ion battery (AZIB) that consist of Zn coated with reduced graphene oxide as the anode and VO·HO/rGO composite as the cathode. The new AZIB exhibits excellent cycle stability with a high capacity retention of 79% after 1000 cycles. Moreover, it can deliver a high power density of 8400 W kg at 77 W h kg and a high energy density of 186 W h kg at 216 W kg, and the former is higher than those of previously reported AZIBs. Our work provides a new perspective in developing rechargeable ZIBs and would greatly accelerate the practical applications of rechargeable ZIBs.

There is a great deal of interest in developing next-generation lithium ion (Li-ion) batteries with higher energy capacity and longer cycle life for a diverse range of applications such as portable electronic devices, satellites, and next-generation electric vehicles. Silicon (Si) is an attractive anode material that is being closely scrutinized for use in Li-ion batteries because of its highest-known theoretical charge capacity of 4200 mAh g −1 .[1] The development of Si-anode Li-ion batteries has been hindered, however, mostly because of the large volumetric changes (up to 400%) that occur upon insertion and extraction of Li ions, and in turn the large electrochemically related stress, which results in electrode pulverization, loss of electrical contact, and early capacity fading of battery cells. [2][3][4][5] Despite this challenge, the extraordinarily high energy capacity of Si in its own right has motivated researchers to develop new techniques that reduce the limitations of Si as a practical anode material. Ultrathin Si films down to 50 nm in thickness have been reported for successful antipulverization and capacity nondegradation over two thousand charge/discharge cycles on roughened current collectors. [6] This result, together with a surge of work on improving the capacity retention of Si anodes such as nanoparticles [7,8] and/or composites, [9][10][11][12] nanowires, [13][14][15] or nanotubes [16,17] have shown improved performances, where the nanoforms of materials can offer expansion spaces during lithium insertion/extraction ( Figure 1A). However, some degree of capacity fading still exists due to the limited space for accommodating the facile strain expansion as well as decreased accessibility of the electrolyte to the solid -electrolyte interphase (SEI) between the silicon nanostructures and electrolyte. Here, we present a new strategy of stress relaxation for Si films using an elastomeric substrate that will establish an alternative route for new electrode design. In addition, the design of the anodes offers more efficient ion and electron transport than the reported work that uses nanoparticles, nanowires, or nanotubes.The general concept of stress relaxation can be understood using an eigen strain analogy. It is well-known that the eigen deformation of a free-standing material does not lead to mechanical stress, but only to self-compatible deformations, and eigen-strain-induced stresses are generated when the eigen strain is constrained. Consequently, the stress can be released by removing these constraints (e.g., stainless steel [13] and rough substrates [6] ). Herein, we report an approach in which the rigid substrates (e.g., current collectors) that constrain the "free" expansion/contraction of the Si anodes during charge/ discharge are replaced by soft substrates. The mechanism for stress relaxation is that the volumetric strain in Si that is induced by charge/discharge cycling can buckle the flat Si thin films when they are on soft substrates ( Figure 1B), which in turn releases the stress ...

Aerogel fibers with ultrahigh porosity, large specific surface area, and ultralow density have shown increasing interest due to being considered as the next generation thermal insulation fibers. However, it is still a great challenge to fabricate arbitrary aerogel fibers via the traditional wet-spinning approach due to the obvious conflict between the static sol–gel transition of the aerogel bulks and the dynamic wet-spinning process of aerogel fibers. Herein, a sol–gel confined transition (SGCT) strategy was developed for fabricating various mesoporous aerogel fibers, in which the aerogel precursor solution was first driven by the surface tension into the capillary tubes, then the gel fibers were easily formed in the confined space after static sol–gel process, and finally the mesoporous aerogel fibers were obtained via the supercritical CO2 drying process. As a typical case, the polyimide (PI) aerogel fiber prepared via the SGCT approach has exhibited a large specific surface area (up to 364 m2/g), outstanding mechanical property (with elastic modulus of 123 MPa), superior hydrophobicity (with contact angle of 153°), and excellent flexibility (with curvature radius of 200 μm). Therefore, the aerogel woven fabric made from PI aerogel fibers has possessed an excellent thermal insulation performance in a wide temperature window, even under the harsh environment. Besides, arbitrary kinds of aerogel fibers, including organic aerogel fibers, inorganic aerogel fibers, and organic–inorganic hybrid aerogel fibers, have been fabricated successfully, suggesting the universality of the SGCT strategy, which not only provides a way for developing aerogel fibers with different components but also plays an irreplaceable role in promoting the upgrading of the fiber fields.

This paper demonstrates that fine‐grained (2–3 μm), transparent Nd:YAG can be achieved at SiO2 doping levels as low as 0.02 wt% by the sinter plus hot isostatic pressing (HIP) approach. Fine grain size is assured by sintering to 98% density, in order to limit grain growth, followed by HIP. Unlike dry‐pressed samples, tape‐cast samples were free of large, agglomerate‐related pores after sintering, and thus high transparency (i.e., >80% transmission at 1064 nm) could be achieved by HIP at <1750°C along with lower silica levels, thereby avoiding conditions shown to cause exaggerated grain growth. Grain growth was substantially limited at lower SiO2 levels because silica is soluble in the YAG lattice up to ∼0.02–0.1 wt% at 1750°C, thus allowing sintering and grain growth to occur by solid‐state diffusional processes. In contrast, liquid phase enhanced densification and grain growth occur at ∼0.08–0.14 wt% SiO2, especially at higher temperatures, because the SiO2 solubility limit is exceeded.

Dempster-Shafer evidence theory (D-S theory) has been widely used in many information fusion systems since it was proposed by Dempster and extended by Shafer. However, how to determine the basic probability assignment (BPA), which is the main and first step in D-S theory, is still an open issue, especially when the given environment is in an open world, which means the frame of discernment is incomplete. In this paper, a method to determine generalized basic probability assignment in an open world is proposed. Frame of discernment in an open world is established first, and then the triangular fuzzy number models to identify target in the proposed frame of discernment are established. Pessimistic strategy based on the differentiation degree between model and sample is defined to yield the BPAs for known targets. If the sum of all the BPAs of known targets is over one, then they will be normalized and the BPA of unknown target is assigned to0; otherwise the BPA of unknown target is equal to1minus the sum of all the known targets BPAs. IRIS classification examples illustrated the effectiveness of the proposed method.

Heterogeneous interface design to boost interfacial polarization has become a feasible way to realize high electromagnetic wave absorbing (EMA) performance of dielectric materials. However, interfacial polarization in simple structures such as particles, rods, and flakes is weak and usually plays a secondary role. In order to enhance the interfacial polarization and simultaneously reduce the electronic conductivity to avoid reflection of electromagnetic wave, a more rational geometric structure for dielectric materials is desired. Herein, a Ti 3 C 2 T x /MoS 2 self-rolling rod-based foam is proposed to realize excellent interfacial polarization and achieve high EMA performance at ultralow density. Different surface tensions of Ti 3 C 2 T x and ammonium tetrathiomolybdate are utilized to induce the self-rolling of Ti 3 C 2 T x sheets. The rods with a high aspect ratio not only remarkably improve the polarization loss but also are beneficial to the construction of Ti 3 C 2 T x /MoS 2 foam, leading to enhanced EMA capability. As a result, the effective absorption bandwidth of Ti 3 C 2 T x /MoS 2 foam covers the whole X band (8.2-12.4 GHz) with a density of only 0.009 g cm −3 , at a thickness of 3.3 mm. The advantages of rod structures are verified through simulations in the CST microwave studio. This work inspires the rational geometric design of micro/nanostructures for new-generation EMA materials.

Identifying strategies for beneficial band engineering is crucial for the optimization of thermoelectric (TE) materials. In this study, we demonstrate the beneficial effects of ionic dopants on n‐type Mg3Sb2. Using the band‐resolved projected crystal orbital Hamilton population, the covalent characters of the bonding between Mg atoms at different sites are observed. By partially substituting the Mg at the octahedral sites with more ionic dopants, such as Ca and Yb, the conduction band minimum (CBM) of Mg3Sb2 is altered to be more anisotropic with an enhanced band degeneracy of 7. The CBM density of states of doped Mg3Sb2 with these dopants is significantly enlarged by band engineering. The improved Seebeck coefficients and power factors, together with the reduced lattice thermal conductivities, imply that the partial introduction of more ionic dopants in Mg3Sb2 is a general solution for its n‐type TE performance. © 2019 Wiley Periodicals, Inc.