Property by design is one appealing idea in material synthesis but hard to achieve in practice. A recent successful example is the demonstration of van der Waals (vdW) heterostructures, 1-3 in which atomic layers are stacked on each other and different ingredients can be combined beyond symmetry and lattice matching. This concept, usually described as a nanoscale Lego blocks, allows to build sophisticated structures layer by layer. However, this concept has been so far limited in two dimensional (2D) materials. Here we show a class of new material where different layers are coaxially (instead of planarly) stacked. As the structure is in one dimensional (1D) form, we name it "1D vdW heterostructures". We demonstrate a 5 nm diameter nanotube consisting of three different materials: an inner conductive carbon nanotube (CNT), a middle insulating hexagonal boron nitride nanotube
Bulk amorphous materials have been studied extensively and are used widely. Yet, their atomic arrangement remains an open issue. They are generally believed to be Zachariasen continuous random networks (Z-CRNs) 1 , but recent experimental evidence favours the competing crystallite model in the case of amorphous silicon 2-4 .Corresponding questions in 2D materials are wide open. Here we report the synthesis of centimetre-scale, freestanding, continuous, and stable monolayer amorphous carbon (MAC), topologically distinct from disordered graphene, by laser-assisted chemical vapour deposition 5 . Unlike bulk materials, the amorphous structure of MAC can be determined by atomic-resolution imaging. Extensive characterisation reveals complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and 5-, 6-, 7-, and 8-member rings. The ring distribution is not a Z-CRN but resembles the competing (nano)crystallite model 6 . A corresponding model has been constructed and enables density-functional-theory calculations of MAC properties, in accord with observations. Direct measurements
Understanding the thermal aggregation behavior of metal atoms is important for the synthesis of supported metal clusters. Here, derived from a metal–organic framework encapsulating a trinuclear FeIII2FeII complex (denoted as Fe3) within the channels, a well‐defined nitrogen‐doped carbon layer is fabricated as an ideal support for stabilizing the generated iron nanoclusters. Atomic replacement of FeII by other metal(II) ions (e.g., ZnII/CoII) via synthesizing isostructural trinuclear‐complex precursors (Fe2Zn/Fe2Co), namely the “heteroatom modulator approach”, is inhibiting the aggregation of Fe atoms toward nanoclusters with formation of a stable iron dimer in an optimal metal–nitrogen moiety, clearly identified by direct transmission electron microscopy and X‐ray absorption fine structure analysis. The supported iron dimer, serving as cooperative metal–metal site, acts as efficient oxygen evolution catalyst. Our findings offer an atomic insight to guide the future design of ultrasmall metal clusters bearing outstanding catalytic capabilities.
Vapor transportation is the core process in growing transition-metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). One inevitable problem is the spatial inhomogeneity of the vapors. The non-stoichiometric supply of transition-metal precursors and chalcogen leads to poor control in products' location, morphology, crystallinity, uniformity and batch to batch reproducibility. While vapor-liquid-solid (VLS) growth involves molten precursors (e.g., non-volatile Na2MoO4) at the growth temperatures higher than their melting points. The liquid Na2MoO4 can precipitate solid MoS2 monolayers when saturated with sulfur vapor. Taking advantage of the VLS growth, we achieved three kinds of important achievements: (i) 4-inch-wafer-scale uniform growth of MoS2 flakes on SiO2/Si substrates, (ii) 2-inch-wafer-scale growth of continuous MoS2 film with a grain size exceeding 100 μm on sapphire substrates, and (iii) pattern (site-controlled) growth of MoS2 flakes and film. We clarified that the VLS growth thus pave the new way for the high-efficient, scalable synthesis of two-dimensional TMDC monolayers.
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