EFFECTS OF SURFACE MODIFICATION AND CROSS-LINKED GRAPHENE OXIDE WITH ETHYLENEDIAMINE ON ELECTRICAL PROPERTIES OF REDUCED GRAPHENE OXIDE FILMS

Cross-linked graphene oxide (GO) films, with simultaneous reduction and surface functionalization, were fabricated through filtration using a pressure-assisted self-assembly technique. Cross-linking between graphene sheets was realized by chemical reaction between ethylenediamine monomers and oxygen functional groups on GO surface in solution. The effect of cross-linking on the electrical properties of functionalized graphene oxide films was investigated. Ethylamine was used to produce uncross-linked graphene films, whose structures and properties were compared to those of graphene films cross-linked with ethylenediamine. The surface modification of GO with ethylamine or ethylenediamine took place under mild conditions with nitrogen protection. The removal of epoxide, carboxyl and hydroxyl groups from GO by ethylamine or ethylenediamine was confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy (XPS). XPS results also demonstrated that both ethylamine and ethylenediamine were chemically bonded to GO. Results show that, after surface modification, the electrical conductivity of GO film modified with ethylenediamine is greatly improved, meanwhile an improvement as high as four orders of magnitude for the unmodified GO film. After annealing at 800°C for 2 hours, the sheet resistance of reduced graphene oxide films modified with ethylenediamine decreased to 1.07 Ω, much lower than that of reduced graphene oxide films (10.63 Ω).

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