Solar-thermal cold-wall chemical vapor deposition reactor design and characterization for graphene synthesis

Abstract

Manufacturing processes are often highly energy-intensive, even when the energy is primarily used for direct heating processes. The required energy tends to derive from local utilities, which currently employ a blend of sources ranging from fossil fuels to renewable wind and solar photovoltaics, among others, when the end manufacturing need is thermal energy. Direct solar-thermal capture provides a compelling alternative that utilizes renewable energy to reduce greenhouse gas emissions from industrial processes, but one that has rarely been employed to date. In this study, a 10 kW[Formula: see text] custom-built high flux solar simulator (HFSS) that closely approximates the solar spectrum produces a heat flux distribution with an adjustable peak between 1.5 and 4.5 MW/m[Formula: see text]. The HFSS system is coupled to a cold-wall chemical vapor deposition (CVD) system that is equipped to automate graphene synthesis while providing safe operation, precise control, and real-time monitoring of process parameters. A numerical heat transfer model of a thin copper substrate is derived and validated to compute the substrate’s temperature profile prior to the synthesis process. The peak substrate temperature is correlated to the HFSS supply current and vacuum pressure, as it serves as a critical design parameter during graphene synthesis. We report the synthesis of high-quality graphene films on copper substrates with an average Raman peak intensity ratio [Formula: see text] of 0.17. Backscattered electron microscopy reveals a characteristic grain size of 120 [Formula: see text]m, with an area ratio of 16 when compared to that of low-quality graphene on copper. The reported solar-thermal CVD system demonstrates the ability to produce a high-value product, namely, graphene on copper, directly from a renewable energy resource with process control and automation that enables synthesis under a variety of conditions.

High-Quality AB Bilayer Graphene Films by Direct Solar-Thermal Chemical Vapor Deposition

“…Consequently, a larger area on the copper substrate with a circular area of a 20 mm radius achieves a more spatially uniform temperature of 1060 ± 10 °C, by increasing the total power emitted by the HFSS. Using a custom thermal model validated in prior work 48 and IR temperature measurements (at r = 0 and 20 mm), an inverse model for the substrate and conditions used here is shown in Figure S1, and the results indicate steady-state temperature uniformity within 10 °C up to a radius of 20 mm. Such an approach was investigated to study film uniformity, enlargement, and coverage under the same synthesis conditions.…”

“…The substrate is heated and annealed under a hydrogen atmosphere prior to graphene growth, and a single-wavelength (5 μm) pyrometer (Williamson, SP-GL-20C) calibrated to the melting point of copper is used to measure its temperature (an average value within a circular diameter of 3.8 mm). The copper substrate reaches a constant temperature of 1060 °C within a circular area of a 6 mm radius, where the heat flux is most concentrated, in 15 min . The heat flux profile gradually drops with radial distance due to the use of an ellipsoidal reflector that provides a Gaussian–Lorentzian heat flux distribution.…”

“…The copper substrate reaches a constant temperature of 1060 °C within a circular area of a 6 mm radius, where the heat flux is most concentrated, in 15 min. 48 The heat flux profile gradually drops with radial distance due to the use of an ellipsoidal reflector that provides a Gaussian−Lorentzian heat flux distribution. Accordingly, the substrate's temperature gradient with radial distance takes a similar profile due to the HFSS's dominant effect on heat transfer.…”

“…Accordingly, the substrate's temperature gradient with radial distance takes a similar profile due to the HFSS's dominant effect on heat transfer. Prior work 48 has revealed a strong correlation between the substrate radial temperature profile and graphene quality (I D /I G ). Enlargement of the peak heating area was achieved by displacing the lamp 4.8 mm toward the target (Z axis shown in Figure 1), out of its focal plane, where the heat flux on the sample is flattened to produce a more uniform profile (see Figure S1), and the current supply to the HFSS is increased to compensate for the reduction in peak heat flux.…”

Sequential Bayesian-optimized graphene synthesis by direct solar-thermal chemical vapor deposition

“…A custom-built CVD system equipped with a metered gas supply, vacuum pump, and water-cooled stainless steel reactor with a 25.4 cm quartz viewport has been integrated with the HFSS in previous work [44]. The system includes mass flow controllers (MKS, GM50A) calibrated for CH 4 and H 2 with flow rates up to 100 and 1000 sccm, respectively, a capacitance manometer (MKS, 624F) in the range of 1000 torr, a rotary vane vacuum pump (Oerlikon-Leybold, D65BCS), and a control throttle valve (MKS, T3BI).…”