Effect of the Plasma Gas Composition on the Properties of Graphene
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MA CHEMISTRY
Effect of the Plasma Gas Composition on the Properties of Graphene M. B. Shavelkinaa, *, P. P. Ivanova, A. N. Bocharova, and R. Kh. Amirova aJoint
Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received March 27, 2020; revised March 27, 2020; accepted April 20, 2020
Abstract—Theoretical and experimental studies of the synthesis of graphene with the introduction of nitrogen into a jet of helium plasma generated by a direct-current plasma torch with a power of to 40 kW at a pressure of 350 Torr have been performed. A propane–butane mixture was used as a source of carbon. As found by scanning microscopy, Raman scattering, and synchronous thermal analysis, the morphology of the synthesis products changed from graphene flakes to carbon nanotubes upon the addition of nitrogen in a ratio of 1 : 1.22 to the jet of helium plasma. The numerical modeling of the process showed that cyanopolyyne molecules, HC9N and HC11N, containing many carbon atoms appeared instead of C60 and C80 in the jets of helium upon the addition of nitrogen. Keywords: synthesis, plasma, hydrocarbon conversion, graphene, carbon nanotubes, quasi-one-dimensional flow DOI: 10.1134/S0018143920050136
INTRODUCTION As is well known, the introduction of impurities into crystal lattices is the most effective way to control the properties of crystals [1]. This effect was also observed in nanosized structures. A series of experimental and theoretical works was devoted to methods used for introducing various impurity atoms into the lattices of carbon nanotubes and graphene and to the characterization of the resulting heterostructures. It was found [2, 3] that adsorption on a carbon network (or on edge sections, for example, of graphene ribbons) rather than incorporation into the lattice was characteristic of N, F, Co, Fe, Au, Pt, Gd, and O atoms. This was confirmed by studies of N-graphene, which was synthesized using a microwave discharge [4]. The heterostructures obtained based on graphene or carbon nanotubes already have great potential for use in microelectronics, chemical sources of electric energy, medicine, etc. [5–7]. The aim of this work was to study the selective synthesis of carbon nanostructures by the conversion of hydrocarbons in plasma jets of variable composition generated by a powerful direct current plasma torch. EXPERIMENTAL The setup for the plasma-chemical synthesis of carbon nanostructures included a direct-current plasma torch with an expanding output anode, a vacuum chamber, a water ring pump, water cooling systems, energy supply systems, pressure sensors, flow meters, and thermocouples (Fig. 1). The experimental
setup was described in detail by Shavelkina and Amirov [8]. The method consisted in the simultaneous supply of a mixture of hydrocarbons with a plasma-forming gas into a plasma torch, where carbon vapor was formed; deposited soot was formed in the reactor flow path upon the subsequent rapid cooling of this vapor. The hydrocarbon feed rate, the plasma
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