Substrate-free gas-phase synthesis of graphene.

摘要

Graphene is a single atomic layer of sp2-bonded carbon atoms tightly packed in a two-dimensional honeycomb lattice. The material possesses remarkable properties and has been envisioned for use in numerous applications. Contemporary graphene production techniques require substrates or graphite crystals to create graphene. Furthermore, these approaches involve multiple steps, and sometimes non-ambient conditions, to produce atomically-thin sheets. This dissertation presents the first substrate-free gas-phase graphene synthesis method. The technique can synthesize graphene in a single step at atmospheric pressure, without the use of graphite or substrates.;The novel synthesis method was discovered through experiments that tested the hypothesis that graphene could be synthesized through the delivery of alcohols into argon plasmas. The experiments presented in this dissertation were conducted in an atmospheric-pressure microwave plasma reactor.;Solid carbon materials were produced by delivering liquid ethanol droplets directly into argon plasmas. Numerous characterization techniques were used to unambiguously prove that the synthesized materials were clean and highly ordered graphene sheets.;Additional studies investigated the effects of variable experimental parameters on the graphene synthesis process. The applied microwave power did not significantly affect the types of structures produced in the reactor. Lowering the volumetric flow rate of the plasma gas resulted in the synthesis of graphitic particles. The composition of the precursors delivered into the reactor also affected graphene synthesis. Graphene was not produced through the delivery of methanol or isopropyl alcohol droplets. However, graphene was obtained through dimethyl ether, which is an organic compound with the same atomic composition as ethanol. Thus, the flow rate and precursor composition significantly affected the nucleation, growth, and residence time of the materials created during experiments.;A practical application for the synthesized graphene is also presented in this dissertation. The sheets were found to be an ideal support structure for the transmission electron microscopy characterization of nanoparticles coated with molecular layers.;The substrate-free gas-phase method is capable of rapid and continuous graphene synthesis at ambient pressure. The simplicity of the approach makes it scalable for industrial graphene production. The novel technique presented in this dissertation could substantially enable graphene research and applications.