Although atomic vacancies in monolayer 2D materials have been ideal candidates for theoretical simulations and modeling of gas flows ( 4, 20– 22), they have not been studied extensively in experiments ( 9, 14). Despite the emergence of many nanoscale gas flow conduits such as nanopores ( 5– 9), nanotubes ( 10– 12), nanochannels ( 11, 13– 16), nanolaminates ( 17, 18), etc., ultimately narrow quasi–zero-dimensional (0D) apertures with atomic-scale dimensions in both the transmembrane and lateral directions, which challenge the applicability of the Knudsen equation for gas flows, have been limited ( 5, 8, 9, 19). In the cases where the membrane surface can adsorb gases, the flow is a combination of direct transmission through the pore and diffusion along the membrane surface ( 4). From a theory standpoint, a pore or an aperture is a simple model system through which gas transmission is proportional to the impingement of gas molecules, i.e., likelihood of a gas molecule encountering a pore, and the activation barrier, if any, to cross the pore.
A2 small vs big aperture free#
This is known as the free molecular regime, and the gas flux through these pores was comprehensively described using the Knudsen equation ( 2), which has been modified and adapted to explain the flows through various confined systems ( 3). In extremely narrow pores, the mean free path of a gas is much larger than that of the dimensions of the pore itself, which leads to gas dynamics dominated by molecular collisions with walls of the pore rather than the intermolecular collisions ( 2). Understanding confined gas flows in angstrom-scale tight spaces plays a major role not only in the design of gas extraction techniques but also for gas separation and production ( 1). We propose a simple yet robust method for confirming the formation of atomic apertures over large areas using gas flows, an essential step for pursuing their prospective applications in various domains including molecular separation, single quantum emitters, sensing and monitoring of gases at ultralow concentrations. WS 2 monolayers with atomic apertures are mechanically sturdy and showed fast helium flow. Atomic vacancies from missing tungsten (W) sites are made in freestanding (WS 2) monolayers by focused ion beam irradiation and characterized using aberration-corrected transmission electron microscopy. We establish that pristine monolayer tungsten disulfide (WS 2) membranes act as atomically thin barriers to gas transport. Here, we report atomic-scale defects in two-dimensional (2D) materials as apertures for gas flows at the ultimate quasi-0D atomic limit. Gas flows are often analyzed with the theoretical descriptions formulated over a century ago and constantly challenged by the emerging architectures of narrow channels, slits, and apertures.
0 kommentar(er)
