Impermeable Atomic Membranes from Graphene Sheets
  We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the world's thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick. 
J. Scott Bunch, Scott S. Verbridge, Jonathan S. Alden, Arend M. van   der Zande, Jeevak M. Parpia, Harold G. Craighead, and ...