Patterning Large Free-Standing Reduced Graphene Oxide Films Assisted by Open-Area Copper Substrates for Graphene Drums

The growth of large free-standing reduced graphene oxide films induced by open-area copper substrates is analyzed. This phenomenon, which is initiated by the selfassembly and reduction of graphene oxide flakes on the copper surface and, then, is extended over the open area, has been first observed in grids with millimeter-size holes. In this study, it is reproduced for the first time, using transmission electron microscopy copper microgrids for its detailed examination. Selected area electron diffraction patterns of suspended films synthesized on the microgrids are analyzed as a function of the synthesis period and the concentration of graphene oxide dispersion. For synthesis periods as short as 15 min, extended reduced graphene oxide films spanning the copper strands over the microgrid holes are readily assembled. The number of stacked layers in the films increases quickly with the synthesis period length. By decreasing the concentration of the graphene oxide suspension, the stacking mode of graphene layers is modified. Turbostratic arrangement is observed on free-standing films synthesized for periods longer than 30 min. An estimation of a turbostratic factor for the different analyzed samples indicates that it increases with the synthesis time and the graphene oxide concentration in the reaction medium. Promising results are reported to produce suspended reduced graphene oxide films of tractable properties on open-area copper substrates. These structures are of great interest for the development of graphene membrane drums, with applications as electromechanical resonators for mass or force sensors, or in basic studies to analyze graphene films without perturbations of the underlaying substrates.