Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However, the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation. Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 µm s-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional (2D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2D materials and thus promote their future applications in the photonics and electronics.
Interlayer spacing is expected to influence the properties of multilayer two-dimensional (2D) materials. However, the ability to non-destructively regulate the interlayer spacing bidirectionally and reversibly is challenging. Here we report the preparation of 2D materials with tunable interlayer spacing by introducing active sites (Ce ions) in 2D materials to capture and immobilize Pt single atoms. The strong chemical interaction between active sites and Pt atoms contributes to the intercalation behavior of Pt atoms in the interlayer of 2D materials and further promotes the formation of chemical bonding between Pt atom and host materials. Taking cerium-embedded molybdenum disulfide (MoS2) as an example, intercalation of Pt atoms enables interlayer distance tuning via an electrochemical protocol, leading to interlayer spacing reversible and linear compression and expansion from 6.546 ± 0.039 Å to 5.792 ± 0.038 Å (~11 %). The electronic property evolution with the interlayer spacing variation is demonstrated by the photoluminescence (PL) spectra, delivering that the well-defined barrier between the multilayer and monolayer layered materials can be artificially designed.
Although low‐symmetry lattice structure of 2D transition metals is highly anticipated for both fundamental research and potentially distinctive application, it still has not been experimentally realized, which greatly hinders the exploration of the unique properties. Here, ultra‐thin body‐centered‐cubic (bcc) phase molybdenum (Mo) membranes are successfully synthesized with a low‐symmetry rectangular (110) crystal face via an adsorption‐free reaction. Through experimental and density functional theory studies, no foreign atoms being adsorbed is shown to be a key factor for the successful preparation of the bcc phase 2D transition metal with (110) faces. The realization of 2D Mo(110) with a low‐symmetric rectangular lattice structure extends the scope of 2D structures and is also beneficial for the exploration and development of low‐symmetry rectangular lattice‐structured materials with unique properties.
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