Abstract
Surface conductance of graphene films is investigated in a non-contact microwave cavity operating at 7.4543 GHz. This cavity technique characterizes specimens with high accuracy, without disruption of morphological integrity and without the processing required for definition and application of electrical contacts. The thickness of the conducting 2D material does not need to be explicitly known. Measurement results are illustrated for epitaxial mono-layer graphene formed on 4H-SiC(OOOl) wafers by annealing the substrate via high fidelity Si sublimation. We show that the resonant microwave cavity is sensitive to the surface conductance of atomically thin nano-carbon films. The method is applied to characterize diffusion of water through a thin film moisture barrier coated over epitaxial monolayer graphene. The monolayer graphene is lightly n-type doped and therefore the resulting surface resistance value becomes sensitive to complexation with p-type molecular dopants such as water in moisturized air. Our results suggest that coating graphene surface with 100 nm thick Parylene-C film serves as effective moisture barrier. The observed change in conductance of Parylene-C specimens after environmental stress is within 6% of the pre-test value and would satisfy the typical reliability requirements.
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