An ångström-scale Janus aperture as a gas flow rectifier.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Directional mass transport in confined spaces is vital for biological processes and the water-energy-environment nexus.
• While ionic diodes are understood at the atomic scale, rectifying neutral molecular flow remains a significant challenge.

Purpose of the Study:

• To investigate gas transport and rectification through an ångström-sized Janus aperture in graphene.
• To explore the potential of asymmetric functionalization for controlling molecular flow.

Main Methods:

• Fabrication of a Janus aperture in graphene using feedback-controlled ozone etching.
• Experimental measurement of permeation coefficients for ten different gases.
• High-throughput density functional theory (DFT) calculations and ab initio molecular dynamics simulations.

Main Results:

• Consistent rectified flow observed for seven gases (e.g., Kr, Xe, H2, O2, N2, CO2, N2O), with rectification ratios up to 100 for oxygen.
• Energy barrier-controlled transport mechanism identified, with direction-dependent energy barriers confirmed by DFT.
• Molecular polarizability identified as a key factor influencing rectified gas flow.

Conclusions:

• Ångström-sized Janus apertures in graphene can effectively rectify neutral molecular gas flow.
• The asymmetric functionalization of the aperture is crucial for achieving directional transport.
• Further research is needed to elucidate the role of dipole and higher-order moments in rectification.