Fabrication of angstrom-scale two-dimensional channels for mass transport

Fluidic channels at atomic scales regulate cellular trafficking and molecular filtration across membranes, and thus play crucial roles in the functioning of living systems. However, constructing synthetic channels experimentally at these scales has been a significant challenge due to the limitations in nanofabrication techniques and the surface roughness of the commonly used materials. Angstrom (Å)-scale slit-like channels overcome such challenges as these are made with precise control over their dimensions and can be used to study the fluidic properties of gases, ions and water at unprecedented scales. Here we provide a detailed fabrication method of the two-dimensional Å-scale channel devices that can be assembled to contain a desired number of channels, a single channel or up to hundreds of channels, made with atomic-scale precision using layered crystals. The procedure includes the fabrication of the substrate, flake, spacer layer, flake transfers, van der Waals assembly and postprocessing. We further explain how to perform molecular transport measurements with the Å-channels to directly probe the intriguing and anomalous phenomena that help shed light on the physics governing ultra-confined transport. The procedure requires a total of 1–2 weeks for the fabrication of the two-dimensional channel device and is suitable for users with prior experience in clean room working environments and nanofabrication. Key points Angstrom-scale fluidic devices enable measurement of ballistic gas flows, ultrafast water permeation, steric ion exclusion and voltage gating of currents. The authors detail the fabrication of the substrate, flake, spacer layer and flake transfers, as well as van der Waals assembly and postprocessing. Compared with nanofluidic devices such as nanotubes, lithographically patterned/etched channels and two-dimensional laminates, angstrom-scale channels have atomically flat, pristine and mechanically robust walls with programmable lengths, widths and heights. Angstrom-scale two-dimensional channel devices can be assembled with precise control over their dimensions, as a single channel or hundreds of channels using layered crystals, and enable the measurement of angstrom-scale gas, ion and water fluidics.