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

Nature Protocols volume 19, pages 240–280 (2024)Cite this article

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Abstract

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.

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Fig. 1: Ångstrom-scale channels.
Fig. 2: Flow chart of the Å-scale device fabrication.
Fig. 3: Overview of the fabrication process.
Fig. 4: Molecular transport through Å-channel devices.
Fig. 5: Schematic for the fabrication process of micrometer-size SiNx holes at wafer scale.
Fig. 6: Representative optical images of exfoliated flakes for preparing channels.
Fig. 7: Fabrication of spacers using EBL.
Fig. 8: AFM images of spacers.
Fig. 9: Photograph of the in-house flake transfer setup.
Fig. 10: Schematics of the wet transfer process.
Fig. 11: Device postprocessing to open channels via gold patch.
Fig. 12: Gas flow measurement setup.
Fig. 13: Gravimetric sample holder and measurement setup.
Fig. 14: An electrochemical measurement setup.
Fig. 15: Clewin design file on a 4-inch wafer, with a distance between two windows of 11,000 µm.
Fig. 16: Anticipated results: evaluation of devices.
Fig. 17: Anticipated results: effect of clogging and regeneration of devices.
Fig. 18: Anticipated results: gas flow measurement through the 2D channels device.
Fig. 19: Anticipated results: water flow measurement through 2D channel devices.
Fig. 20: Anticipated results: ion and pressure driven transport measurements in Å-channels.

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Data availability

The main data discussed in this protocol are available in the supporting primary research papers57,59,61,95.

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Acknowledgements

A.K. acknowledges Royal Society research grants (RGS\R2\202036 and IES\R3\203066), EPSRC new horizons grant (EP/V048112/1). B.R. and A.K. acknowledge the EPSRC strategic equipment grant (EP/W006502/1). B.R. acknowledges funding from the Royal Society University Research Fellowship (URF\R1\180127, RF\ERE\210016), Philip Leverhulme Prize PLP-2021-262, EPSRC New Horizons grant EP/X019225/1 and funding from the European Union’s H2020 Framework Programme/European Research Council Starting Grant (852674–AngstroCAP). R.Q. acknowledges a CSC scholarship. All authors are thankful to M. Sellers and D. Mccullagh for their technical support for custom design and manufacturing of electrochemical cells and gas transport holders.

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Authors and Affiliations

  1. National Graphene Institute, The University of Manchester, Manchester, UK

    Ankit Bhardwaj, Marcos Vinicius Surmani Martins, Yi You, Ravalika Sajja, Max Rimmer, Solleti Goutham, Rongrong Qi, Sidra Abbas Dar, Boya Radha & Ashok Keerthi

  2. Department of Physics and Astronomy, School of Natural Sciences, The University of Manchester, Manchester, UK

    Ankit Bhardwaj, Marcos Vinicius Surmani Martins, Yi You, Ravalika Sajja, Max Rimmer, Solleti Goutham, Rongrong Qi, Sidra Abbas Dar & Boya Radha

  3. Department of Chemistry, School of Natural Sciences, The University of Manchester, Manchester, UK

    Ashok Keerthi

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Contributions

A.K., A.B., Y.Y., R.S., R.Q., S.A.D. and M.R. carried out the fabrication of Å-channel devices. A.K., B.R., A.B., R.S. and M.V.S.M. carried out the device characterization. S.G. performed the ion conductance measurements and their analysis. A.B., M.V.S.M., Y.Y., B.R. and A.K. wrote the manuscript with inputs from M.R., R.S. and S.G. All the authors contributed to discussions. A.K. and B.R. provided supervision for the protocol.

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Correspondence to Boya Radha or Ashok Keerthi.

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Key references using this protocol

Radha, B. et al. Nature 538, 222–225 (2016): https://doi.org/10.1038/nature19363

Keerthi, A. et al. Nature 558, 420–424 (2018): https://doi.org/10.1038/s41586-018-0203-2

Gopinadhan, K. et al. Science 363, 145–148 (2019): https://doi.org/10.1126/science.aau6771

Mouterde, T. et al. Nature 567, 87–90 (2019): https://doi.org/10.1038/s41586-019-0961-5

Robin, P. et al. Science 379, 161–167 (2023): https://doi.org/10.1126/science.adc9931

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Bhardwaj, A., Surmani Martins, M.V., You, Y. et al. Fabrication of angstrom-scale two-dimensional channels for mass transport. Nat Protoc 19, 240–280 (2024). https://doi.org/10.1038/s41596-023-00911-x

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