Graphene Nanotunnels: Welcome Onboard with Ashok Keerthi

By Pranoti Kshirsagar /

Manchester is known for making graphene by peeling one layer off a graphite crystal. Ashok Keerthi does the opposite: he removes a layer from the middle of a stack of 2D crystals, leaving tunnels only atoms high, and studies how molecules move through them. In one test, helium came out about a hundred times faster than expected.

About the guest

Ashok Keerthi is a chemist in the Department of Chemistry at the University of Manchester, where he held a Presidential Fellowship at the time of this 2022 recording, a research-focused route equivalent to assistant professor. He studied up to his master’s in India, did a PhD in synthetic organic chemistry at the National University of Singapore, and was a postdoc at the Max Planck Institute for Polymer Research in Germany. His group studies molecular transport through capillaries made with atomic-scale precision and also makes graphene nanoribbons from the bottom up.

Ashok Keerthi curated the Real Scientists Nano Twitter account (@RealSci_Nano) from December 12 to December 20 2022. Read all of Ashok’s tweets from that week.

Key highlights in this episode

  • 03:10 Removing a layer instead of peeling one. Stacking three 2D crystals, with ribbons in the middle as spacers, creates tunnels as thin as one graphene layer: 0.34 nanometres.
  • 07:13 Tunable tunnel height. Adding spacer layers raises the tunnel in steps of 0.34 nm, like setting a height limit that lets bicycles through but stops trucks.
  • 09:27 Chemist on the move. From India to Singapore to Germany, building nanographene molecule by molecule, before moving to Manchester to work on the physics side of graphene.
  • 12:05 Helium at 100 times the speed. A simple test to check the tunnels were clean showed helium flowing about 100 times faster than expected. The atomically smooth walls reflect helium like a mirror, a sign of its wave nature at room temperature.
  • 19:51 One wish, three times over. Funding to recruit great people, to do the research, and to share it with the public and schoolchildren.
Graphene Nanotunnels: Welcome Onboard with Ashok Keerthi
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Why it matters

Because Ashok builds the tunnels himself, he knows their exact size and can calculate what should flow through them. That makes surprises meaningful. Helium came through about 100 times faster than expected because the walls are atomically smooth: helium bounces off them like light off a still lake, showing its wave nature at room temperature. Setting the tunnel height works like a height barrier, letting some molecules through and stopping others. His group is now sending everything from ions to large molecules such as DNA through these tunnels to see how they behave.

Terms explained

In the guest’s own words, with a link to the moment they explain it.

  • Van der Waals heterostructure: different 2D materials stacked together. Ashok stacks three crystals, with ribbons in the middle layer acting as spacers. (Ashok at 04:46)
  • Tunnel height: one graphene layer is 3.4 angstroms (0.34 nanometres) thick, so the tunnel height can be set in multiples of that by choosing how many spacer layers to use. (Ashok at 06:49)
  • Specular reflection: mirror-like reflection off a perfectly flat surface, like mountain peaks reflected in a still lake. Helium reflects this way off the atomically smooth tunnel walls. (Ashok at 15:15)
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Part of Graphene & 2D Materials · Graphene

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