Driven by advanced nanomaterials and nanofabrication technologies, tremendous progress has been made over the last 15 years in making ultrathin membranes based on a variety of advanced nanomaterials and nanotechnologies. Further pushing membrane thickness to sub-50 nm or even atomic level is appealing to researchers, with the ultrafast permeance that may be enabled and ultimate understanding of formation and transport at the extremely low thickness that can be significantly different from ...