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Abstract The transport of water through nanoscale capillaries/pores plays a prominent role in biology, ionic/molecular separations, water treatment and protective applications. However, the mechanisms of water and vapor transport through nanoscale confinements remain to be fully understood. Angstrom-scale pores (~2.8–6.6 Å) introduced into the atomically thin graphene lattice represent ideal model systems to probe water transport at the molecular-length scale with short pores (aspect ratio ~1–1.9) i.e., pore diameters approach the pore length (~3.4 Å) at the theoretical limit of material thickness. Here, we report on orders of magnitude differences (~80×) between transport of water vapor (~44.2–52.4 g m −2 day −1 Pa −1 ) and liquid water (0.6–2 g m −2 day −1 Pa −1 ) through nanopores (~2.8–6.6 Å in diameter) in monolayer graphene and rationalize this difference via a flow resistance model in which liquid water permeation occurs near the continuum regime whereas water vapor transport occurs in the free molecular flow regime. We demonstrate centimeter-scale atomically thin graphene membranes with up to an order of magnitude higher water vapor transport rate (~5.4–6.1 × 10 4  g m −2 day −1 ) than most commercially available ultra-breathable protective materials while effectively blocking even sub-nanometer (>0.66 nm) model ions/molecules. 

Achieving large-size two-dimensional (2D) crystals is key to fully exploiting their remarkable functionalities and application potentials. Chemical vapor deposition growth of 2D semiconductors such as monolayer MoS 2 has been reported to be activated by halide salts, for which various investigations have been conducted to understand the underlying mechanism from different aspects. Here, we provide experimental evidence showing that the MoS 2 growth dynamics are halogen dependent through the Brønsted-Evans-Polanyi relation, based on which we build a growth model by considering MoS 2 edge passivation by halogens, and theoretically reproduce the trend of our experimental observations. These mechanistic understandings enable us to further optimize the fast growth of MoS 2 and reach record-large domain sizes that should facilitate practical applications. 

Scalable graphene synthesis and facile large-area membrane fabrication are imperative to advance nanoporous atomically thin membranes (NATMs) for molecular separations. Although chemical vapor deposition (CVD) allows for roll-to-roll high-quality monolayer graphene synthesis, facile transfer with atomically clean interfaces to porous supports for large-area NATM fabrication remains extremely challenging. Sacrificial polymer scaffolds commonly used for graphene transfer typically leave polymer residues detrimental to membrane performance and transfers without polymer scaffolds suffer from low yield resulting in high non-selective leakage through NATMs. Here, we systematically study the factors influencing graphene NATM fabrication and report on a novel roll-to-roll manufacturing compatible isopropanol-assisted hot lamination (IHL) process that enables scalable, facile and clean transfer of CVD graphene on to polycarbonate track etched (PCTE) supports with coverage ≥99.2%, while preserving support integrity/porosity. We demonstrate fully functional centimeter-scale graphene NATMs that show record high permeances (∼2–3 orders of magnitude higher) and better selectivity than commercially available state-of-the-art polymeric dialysis membranes, specifically in the 0–1000 Da range. Our work highlights a scalable approach to fabricate graphene NATMs for practical applications and is fully compatible with roll-to-roll manufacturing processes. 

Gallium oxide (Ga 2 O 3 ) and its most stable modification, monoclinic β-Ga 2 O 3 , is emerging as a primary material for power electronic devices, gas sensors and optical devices due to a high breakdown voltage, large bandgap, and optical transparency combined with electrical conductivity. Growth of β-Ga 2 O 3 is challenging and most methods require very high temperatures. Nanowires of β-Ga 2 O 3 have been investigated extensively as they might be advantageous for devices such as nanowire field effect transistors, and gas sensors benefiting from a large surface to volume ratio, among others. Here, we report a synthesis approach using a sulfide precursor (Ga 2 S 3 ), which requires relatively low substrate temperatures and short growth times to produce high-quality single crystalline β-Ga 2 O 3 nanowires in high yields. Even though Au- or Ag-rich nanoparticles are invariably observed at the nanowire tips, they merely serve as nucleation seeds while the nanowire growth proceeds via supply and local oxidation of gallium at the substrate interface. Absorption and cathodoluminescence spectroscopy on individual nanowires confirms a wide bandgap of 4.63 eV and strong luminescence with a maximum ∼2.7 eV. Determining the growth process, morphology, composition and optoelectronic properties on the single nanowire level is key to further application of the β-Ga 2 O 3 nanowires in electronic devices. 

Nanowires of layered van der Waals (vdW) crystals are of interest due to structural characteristics and emerging properties that have no equivalent in conventional 3D crystalline nanostructures. Here, vapor-liquid-solid growth, optoelectronics, and photonics of GaS vdW nanowires are studied. Electron microscopy and diffraction demonstrate the formation of high-quality layered nanostructures with different vdW layer orientation. GaS nanowires with vdW stacking perpendicular to the wire axis have ribbon-like morphologies with lengths up to 100 micrometers and uniform width. Wires with axial layer stacking show tapered morphologies and a corrugated surface due to twinning between successive few-layer GaS sheets. Layered GaS nanowires are excellent wide-bandgap optoelectronic materials with Eg = 2.65 eV determined by single-nanowire absorption measurements. Nanometer-scale spectroscopy on individual nanowires shows intense blue band-edge luminescence along with longer wavelength emissions due to transitions between gap states, and photonic properties such as interference of confined waveguide modes propagating within the nanowires. The combined results show promise for applications in electronics, optoelectronics and photonics, as well as photo- or electrocatalysis owing to a high density of reactive edge sites, and intercalation-type energy storage benefitting from facile access to the interlayer vdW gaps.