Controllable Synthesis of Multifunctional, Two-Dimensional Carbon Sheets at Low Temperatures

Abstract

This dissertation studies that a monolithic form of Graphene Oxide (GO) sheets can be physically synthesized on a copper (Cu) surface at low temperatures (≤ 260°C), with tunable oxygen-to-carbon (O/C) composition. In our approach, we build a graphene framework on the reverse side of a Cu foil at a Cu/substrate interface by exploiting the solid-state diffusion of C atoms across a diffusion couple composed of a C-Cu/substrate. A combined experimental and theoretical study shows that the Cu foil provides an effective pathway for C diffusion, trapping the O species dissolved in Cu and enabling the formation of monolithic GO sheets on its surface after an incubation time. In contrast to chemically-derived GO, the as-synthesized GO sheets were electrically active and the O/C composition in GO can be tuned during synthesis process by controlling the O content in the Cu foil prior to the solid-state diffusion process. The resulting GO sheets exhibited tunable bandgap energy by varying the O/C composition, making them potentially useful for flexible and transparent semiconducting applications. The GO films showed the ambipolar transfer characteristics in bottom-gate field-effect transistor (FET) architectures and the electronic properties were found to correlate closely with the bandgap energy. These results suggest that monolithic, two-dimensional chemically-modified C sheets with controllable composition can be prepared at low temperatures, which is highly desirable for graphene-based device production.