Graphene Synthesis by Inductively Heated Copper Foils: Reactor Design and Operation

Abstract

We report on the design of a reactor to grow graphene via inductively heating of copper foils by radio frequency (RF) magnetic fields. A nearly uniform magnetic field induced by Helmholtz-like coils penetrates the copper foil generating eddy currents. While the frequency of the current is being rapidly varied, the substrate temperature increases from room temperature to ~1050 °C in 60 s. This temperature is maintained under Ar/H2 flow to reduce the copper, and under Ar/H2/CH4 to nucleate and grow the graphene over the entire copper foil. After the power cut-off, the temperature decreases rapidly to room temperature, stopping graphene secondary nucleation. Good quality graphene was obtained and transferred onto silicon, and coated with a 300 nm layer of SiO2 by chemical etching of the copper foil. After synthesis, samples were characterized by Raman spectroscopy. The design of the coils and the total power requirements for the graphene induction heating system were first estimated. Then, the effect of the process parameters on the temperature distribution in the copper foil was performed by solving the transient and steady-state coupled electromagnetic and thermal problem in the 2D domain. The quantitative effects of these process parameters were investigated, and the optimization analysis results are reported providing a root toward a scalable process for large-sized graphene.

Computer-aided design of graphene and 2D materials synthesis via magnetic inductive heating of 11 transition metals

“…To grow graphene, we designed and built a specific reactor described in detail in our previous work [4]. The input power was supplied by a 2.4 kW Easyheat (Ambrell) generator working with high-frequency alternating current with a maximum current of 450 A and a frequency of 250 kHz.…”

“…Conduction was reduced by limiting the contact area between the metal and the low thermal conductivity quartz. At high temperatures, the dependence of the radiated power on T 4 is what accounts for the dominance of radiation. But total emittance of the metal, which is integral over wavelength of emissivity that is also wavelength dependent, must be considered.…”

“…The cooling is also extremely fast, with a temperature ramp-down of ∼70 • C s −1 allowing graphene growth to be instantaneously stopped to avoid secondary nucleation. The inductive heating CVD method has been used for growing graphene by Piner et al [1], Seifert et al [2], Wu et al [3], and Pashova et al [4]. Nevertheless, predicting eddy currents and temperature, as well as their spatial distribution in the metal foil, have not yet been fully studied.…”

“…This problem can be overcome by increasing the foil thickness in the limit below the skin depth. Therefore, a copper foil thickness of 125 µm (∼112 mg of Cu cm −2 of graphene) is found to be a good trade-off between inductive heating and chemical etching considerations [1,4]. Using inductive heating of copper substrates, Piner et al [1] achieved graphene-based back-gated field effect transistors with a carrier mobility up to ∼14 000 cm 2 V -1 s -1 under ambient conditions.…”

“…Shape evolution is employed for the identification of competing growth mechanisms including diffusion-limited, attachment-limited, and detachment-limited processes [3]. Pashova et al [4] used Helmholtz-like induction to grow graphene with around a 42.3% monolayer by decomposing methane over 125 µm copper foils at 150 mbar. They showed that it is not necessary to completely decompose the methane in the gas over the substrate and there is no need to heat the overall surrounding gas to obtain good graphene quality.…”