Laser Diagnostics of Plasma in Synthesis of Graphene-Based Materials

Rotational temperature profiles of H2 in a microwave plasma chemical vapor deposition (MPCVD) reactor were measured via coherent anti-Stokes Raman scattering (CARS) spectroscopy. The temperature was found to increase with reactor pressure, plasma generator power, and distance from the deposition surface. At 10 Torr, the measured temperature range was approximately 700–1200 K while at 30 Torr it was 1200–2000 K under the conditions studied. The introduction of CH4 and N2 to the plasma increased the rotational temperature consistently. These findings will aid in understanding the function of the chemical composition and reactions in the plasma environment of these reactors which, to date, remains obscure.