Defect-Mediated Reduction in Barrier for Helium Tunneling through Functionalized Graphene Nanopores

We investigate the separation of helium isotopes by quantum tunneling through graphene nanopores, recently proposed as an alternative to conventional methods for 3He production. We propose here a novel defective nanopore created by removing two pentagon rings of a Stone–Thrower–Wales (STW) defect, which significantly decreases the helium tunneling barrier by 50–75%. The barrier height is fine-tuned by adjusting the effective pore size, which is achieved by pore rim passivation using an appropriate functionalizing atom. This fine-tuning leads to positive deviation in the tunneling probability of 3He compared to that of 4He in the low-energy region, and thereby to high selectivity and transmission of the former isotope. It is found that fluorine-passivated nanopores restrict helium atom penetration because of their highly reduced pore size. Defective nanopores in nitrogen- and oxygen-passivated structures exhibit relatively high transmission values of 10–3 for the oxygen variant and improved selectivity val...