Large Area Films of Alternating Graphene-Carbon Nanotube Layers Processed in Water

We report the preparation of hybrid paperlike films consisting of alternating layers of graphene (or graphene oxide) and different types of multiwalled carbon nanotubes (N-doped MWNTs, B-doped MWNTs, and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized, and we found electrical resistivities as low as 3 x 10(-4) Omega cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field of ca. 0.55 V/mu m, beta factor as high as of 15.19 x 10(3), and operating currents up to 220 mu A. These values are significantly enhanced when compared to previous reports in the literature for other carbon nanostructured filmlike materials. We believe these hybrid foils could find other applications as scaffolds for tissue regeneration, thermal and conducting papers, and laminate composites with epoxy resins.