2D Mo2C has drawn considerable interest recently for its excellent properties in 2D superconductivity and enhanced hydrogen evolution reaction (HER). Liquid metals have been demonstrated to be an ideal substrate for large-area 2D Mo2C growth. However, the growth mechanism of 2D Mo2C on liquid metals has rarely been explored. Here we report the synthesis of high-quality 2D Mo2C crystals and Mo2C/graphene heterostructures on liquid Au by chemical vapor deposition method. A sunk growth mode of 2D Mo2C on liquid Au substrates has revealed, by atomic force microscope characterizations, that some Mo2C crystals grow below the level of Au terraces around tens of nanometers. Furthermore, graphene/Mo2C heterostructure is controllably synthesized by tuning the hydrogen/carbon ratio, which is proven to be an enhanced electrocatalyst for HER against pure Mo2C crystal grown on liquid Au substrates.

The interface between metals and semiconductors plays an essential role in two-dimensional electronic heterostructures, which has provided an alternative opportunity to realize next-generation electronic devices. Lattice-matched two-dimensional heterointerfaces have been achieved in polymorphic 2D transition-metal dichalcogenides MX 2 with M = (W, Mo) and X = (Te, Se, S) through phase engineering; yet other transition-metal chalcogenides have been rarely reported.Here we show that a single layer of hexagonal Cu 2 Te crystal could be synthesized by one-step liquid−solid interface growth and exfoliation. Characterizations of atomically resolved scanning tunneling microscope reveal that the Cu 2 Te monolayer consists of two lattice-matched distinct phases, similar to the 1T and 1T′ phases of MX 2 . The scanning tunneling spectra identify the coexistence of the metallic 1T and semiconducting 1T′ phases within the chemically homogeneous Cu 2 Te crystals, as confirmed by density functional theory calculations. Moreover, the two phases could form nanoscale lattice-matched metal− semiconductor junctions with atomically sharp interfaces. These results suggest a promising potential for exploiting atomicscale electronic devices in 2D materials.

Monolayer and multilayer NaCl(001) films are grown on an Ir(111) substrate, and strain relaxation modes are investigated by scanning tunneling microscopy (STM) and density functional theory calculations. We report that monolayer NaCl(001) exhibits an apparent one-dimensional periodic buckling along the [010] direction, which separates one-dimensional domains of pristine lattices. An atomic model of the monolayer NaCl(001)-(2 × 6) lattice on an Ir(111)-(4 × 7 3 ) substrate is proposed, and related simulation reproduces all the STM features. The calculations suggest that the 4–6 symmetry incompatibility of the NaCl(001)/Ir(111) interface leads to the formation of domain boundaries with alternately arranged top-sited and bridge-sited adatom lines along [100], resulting in one-dimensional atomic buckling. We also observe that the atomic buckling is veiled as the NaCl(001) increases to bilayer and above, suggesting that this relaxation mode is finely tuned by the crystal thickness.

Ultrafast water transport in graphitic nanoenvironment is fundamentally important in the research of biomimetic membranes for potential applications in separation and energy. Yet, the form of graphitic nanostructures has not been fully explored with only carbon nanotubes and graphene nanochannels reported. Here, we fabricated dynamic graphene bubbles via strain engineering of chemical vapor deposition (CVD)-grown graphene on metal substrates. These graphene bubbles could switch between an inflated state and a deflated state continuously with the control of environmental moisture flow. It is demonstrated that water vapors transport through graphene wrinkles and condense inside graphene bubbles. The water transport rates across these graphene bubbles were calculated via dynamic Newton rings, which is comparable to that of carbon nanotubes and aquaporin. The discovery of dynamic graphene bubbles hosting the ability of fast water transport is helpful for an advanced understanding of the nanofluidic phenomenon and its future applications.

Direct growth of single-crystal compound semiconductors on nonepitaxial substrates is a promising route for device processing simplification in electronic and optoelectronic applications. However, the nonepitaxial growth technique for 2D single crystals is still a fundamental challenge. Here, we demonstrate that the macroscopic 2D interface of liquid metals and nonepitaxial solid substrates could be universally designed for the chemical vapor deposition growth of crystalline compound semiconductors. By adopting a sandwiched solid metal/liquid metal/solid substrate environment, millimeter-scale 2D GaS, 2D GaSe, and 1D GaTe single crystals of high quality were synthesized at the interface of liquid gallium and nonepitaxial substrates. Evidence shows that the particle-catalyst-free vapor–liquid–solid growth is driven by screw dislocations. Furthermore, we successfully extend the growth strategy to various metal chalcogenides (Sn, In, Cu, and Ag) and pnictides (Sb). Our work opens up a new route for the direct growth of single-crystalline compound semiconductors on nonepitaxial substrates.