metallic), is a new sensation in the flatland. [1][2][3] Incidentally, among various 2D materials, while boron nitride (BN) has large Young's modulus but compromised mobility, phosphorene and silicene have appreciable carrier mobility but compromised elastic behavior. [4] Graphene, considered the wonder material of this century fairs exceedingly well and its carrier mobility, as well as Young's modulus, are simultaneously high, which places it at a different pedestal. [5,6] However, e-h symmetry and spin symmetry in graphene result in insufficient signal/noise ratio in electronic as well as spintronic chips. [7] Borophene, being metallic in both β 12 and X 3 crystallographic phases, also has excellent elastic strength and electronic mobility, which altogether places it at a significant pedestal among 2D materials. The evolution of borophene is expected to bring in new dimensions to 2D-materialbased next-generation devices [8] (see the schematic plot in Figure 1a for the comparative presentation of ln (mobility) vs Young's modulus for various 2D materials). [9][10][11][12][13] Anisotropic atomic ordering results in enhanced electronic mobility ≈1.82 × 10 6 cm 2 V −1 s −1 , Young's modulus ≈398 N m −1 , and thermal conductivity along atomic ridgelines. [14,15] In particular, for flexible electronic as well as spintronic chip applications, high electron mobility and Young's modulus are desirable simultaneously and borophene Borophene, the lightest among all Xenes, possesses extreme electronic mobility along with high carrier density and high Young's modulus. To accomplish device-quality borophene, novel approaches of realization of monolayers need to be urgently explored. In this work, micromechanical exfoliation is discovered to result in mono-and few-layered borophene of device quality. Borophene sheets are successfully fabricated down to monolayer thickness. Distinct crystallographic phases of borophene viz. XRD study reveals crystallographic phase transition from rhombohedral to several other eigen phases of borophene. The role of the destination substrates is held crucial in determining the final phase of the transferred sheet. The exfoliation energy is calculated by density functional theory. Molecular dynamics simulations are used to simulate the exfoliation process. Heterolayers of borophene, with black phosphorene (BP) or with molybdenum disulfide (MoS 2 ) atomic sheets, are found to result in photoexcited coupling quantum states. Gold-coated borophene bestows promising anchoring capability for surface-enhanced Raman spectroscopy (SERS). Successful demonstration of the electronic behavior of micromechanically exfoliated borophene and excitonic behavior of borophene-based heterolayers will guide future generation devices not only in electronics and excitonics, but also in thermal management, electronic packaging, hydrogen storage, hybrid energy storage, and clean energy solutions.
With the emergence of graphene, the first two-dimensional (2D) material, many other 2D materials have been discovered and examined for novel applications. Various synthesis approaches have been employed for 2D Xenes, nitrides, carbide, and oxides to obtain high-quality and large-quantity production. Among them, 2D oxides have gained researcher’s attention for their magnetic, electronic, and catalytic properties. In this Article, we report single-step and scalable synthesis of hematene (a 2D atomic layer of iron oxide (Fe2O3)) and 2D metal oxides (2DMOs), e.g., chromium oxide, copper oxide, etc., by following a similar synthesis protocol. Metal chlorides dispersed in dimethylformamide (DMF) solvent immediately convert to the corresponding metal oxides upon microwave irradiation. Direct microwave solid-phase synthesis has also been explored and compared with liquid-phase microwave synthesis of hematene. Crystallographic structures of synthesized hematene were obtained by high-resolution transmission electron microscopy (HRTEM) and chemical identification was done by X-ray photoelectron (XPS) and Raman spectroscopy. In addition, magnetic measurements reveal the room-temperature ferromagnetic ordering of hematene with a saturation magnetization of 0.24 emu/g (at 300 K) and 1.08 emu/g (at 60 K). Field-cooled and zero-field cooled measurements clearly demonstrate a high Curie temperature of ∼376 K. Versatility of the synthesis technique has been demonstrated by employing the same protocol to the successful synthesis of a variety of metal oxides. This synthesis route permits a simple, inexpensive, efficient, and scalable production of 2DMOs.
Solar‐driven photothermal water evaporation is considered an elegant and sustainable technology for freshwater production. The existing systems, however, often suffer from poor stability and biofouling issues, which severely hamper their prospects in practical applications. Conventionally, photothermal materials are deposited on the membrane supports via vacuum‐assisted filtration or dip‐coating methods. Nevertheless, the weak inherent material‐membrane interactions frequently lead to poor durability, and the photothermal material layer can be easily peeled off from the hosting substrates or partially dissolved when immersed in water. In the present article, the discovery of the incorporation of borophene into cellulose nanofibers (CNF), enabling excellent environmental stability with a high light‐to‐heat conversion efficiency of 91.5% and water evaporation rate of 1.45 kg m−2 h−1 under simulated sunlight is reported. It is also demonstrated that borophene papers can be employed as an excellent active photothermal material for eliminating almost 100% of both gram‐positive and gram‐negative bacteria within 20 min under three sun irradiations. The result opens a new direction for the design of borophene‐based papers with unique photothermal properties which can be used for the effective treatment of a wide range of wastewaters.
Borophene (B), possessing remarkably unique chemical binding in its crystallographic structural phases including anisotropic structures, theoretically has high Young’s modulus as well as thermal conductivity and moreover, it is metallic...
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