Graphene gas osmometers

We show that graphene membranes that separate two gases at identical pressure are deflected by osmotic pressure. The osmotic pressure is a consequence of differences in gas permeation rates into a few-layer graphene enclosed cavity. The deflection of the membrane is detected by measuring the tension-induced resonance frequency with an interferometric technique. Using a calibration measurement of the relation between resonance frequency and pressure, the time dependent osmotic pressure on the graphene is extracted. The time dependent osmotic pressure for different combinations of gases shows large differences that can be accounted for by a model based on the different gas permeation rates. In this way, a graphene-membrane based gas osmometer with a responsivity of ∼60 kHz mbar^–1 and nanoscale dimensions is demonstrated. (letter)