Intrinsic wettability of CVD-grown graphene on Cu/α-Al2O3(0 0 0 1) to ionic liquid [emim][NTf2] was investigated by in situ contact angle measurement in a high vacuum. The contact angles increased with the coverage of graphene from a complete wetting regime on the clean Cu surface to a partial wetting regime on the surface fully covered with graphene. The measured contact angles were well explained by the Cassie equation. Since the contact angle of graphene was close to that of bulk HOPG, it is indicated that the first layer graphene is just enough to govern its wettability.
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