Nature Materials, Published online: 25 February 2026; doi:10.1038/s41563-026-02513-wGas transport through an ångström-sized Janus aperture in graphene, which is created by ozone etching, is investigated by using high-resolution transport measurements and high-throughput atomistic simulations. Rectified gas flow for various gases is demonstrated with rectification ratios of up to two orders of magnitude for oxygen.