Microwave plasma enabled synthesis of free standing carbon nanostructures at atmospheric pressure conditions

Abstract

An experimental and theoretical study on microwave (2.45 GHz) plasma enabled assembly of carbon nanostructures, such as multilayer graphene sheets and nanoparticles, was performed. The carbon nanostructures were fabricated at different Ar-CH4 gas mixture composition and flows at atmospheric pressure conditions. The synthesis method is based on decomposition of the carbon-containing precursor (CH4) in the "hot" microwave plasma environment into carbon atoms and molecules, which are further converted into solid carbon nuclei in the "colder" plasma zones. By tailoring of the plasma environment, a controlled synthesis of graphene sheets and diamond-like nanoparticles was achieved. Selective synthesis of graphene flakes was achieved at a microwave power of 1 kW, Ar and methane flow rates of 600 sccm and 2 sccm respectively, while the predominant synthesis of diamond-like nanoparticles was obtained at the same power, but with higher flow rates, i.e. 1000 and 7.5 sccm, respectively. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the 'hot' plasma zone and to determine the main plasma parameters. Raman spectroscopy and scanning electron microscopy have been applied to characterize the synthesized nanostructures. A previously developed theoretical model was further updated and employed to understand the mechanism of CH4 decomposition and formation of the main building units, i.e. C and C2, of the carbon nanostructures. An insight into the physical chemistry of carbon nanostructure formation in a high energy density microwave plasma environment is presented.

Effects of Buffer Gases on Graphene Flakes Synthesis in Thermal Plasma Process at Atmospheric Pressure

“…The effects of process parameters on the graphene flakes synthesis in a thermal plasma process have been reported in some studies. For example, Dato et al [14][15][16][17], Tatarova et al [18][19][20], and Melero et al [21,22] established a single-step method to synthesize graphene flakes with few layers based on microwave plasma. Their research revealed that factors influencing graphene flakes synthesis include the precursor type, reactor design, flow rate of buffer gas, etc.…”

Graphene synthesized in atmospheric plasmas—A review

“…Recently, the delivery of methane (CH 4 ) into atmospheric Ar plasmas resulted in the production of relatively small amounts of GSG sheets among carbon nanoparticles. 52 This result suggests that O may not be required for the formation of GSG. A carboncontaining gas, such as acetylene (C 2 H 2 ), could potentially be used to produce GSG since it is a precursor for the formation of aromatic nuclei and does not contain oxygen that results in the creation of CO.…”

“…A carboncontaining gas, such as acetylene (C 2 H 2 ), could potentially be used to produce GSG since it is a precursor for the formation of aromatic nuclei and does not contain oxygen that results in the creation of CO. The synthesis of GSG through the use of dimethyl ether 26 or methane 52 demonstrates that ethanol is not the sole precursor for GSG formation. Future GSG studies should investigate the use of gaseous precursors that can facilitate the production of GSG, since the use of gases eliminates the additional time and energy required to atomize or vaporize ethanol.…”

“…The morphology of crumpled graphene has been compared with that of crumpled paper. 43,52 However, GSG may be crumpled because of the presence of graphitic nanocrystals in the synthesized sheets. 71 In situ TEM has revealed that graphitic nanocrystals provide GSG with additional mechanical stability, enable the material to reversibly deform, and prevent GSG from being flattened like paper.…”

Graphene synthesis by microwave plasma chemical vapor deposition: analysis of the emission spectra and modeling

“…Trinsoutrot et al proposed a chemical mechanism for methane pyrolysis on copper foil within a computational fluid dynamics (CFD) model to investigate the role of the gas phase in graphene formation [79]. The team led by Prof. E. Tartarova studied the synthesis of freestanding graphene sheets from the decomposition of ethanol vapor in atmospheric-pressure microwave argon plasma [80,81]. Their model considers the decomposition of ethanol/argon/hydrogen in microwave plasma through 57 species and 394 homogeneous reactions.…”