Influence of plasma power on deposition rate, crystallinity, and hydrogen desorption in methane-derived carbon nanoparticles

Carbon nanoparticles are highly valued for applications in electronics, energy storage, and catalysis, yet their synthesis from methane is hindered by its chemical stability and the difficulty of controlling carbon bonding in reactive environments. In the present study, methane was dissociated using a non-thermal plasma in an argon environment at reduced pressure. The effects of plasma power and residence time on the nanoparticles were investigated through extensive characterization, showing that the plasma power controlled both the deposition rates and crystallinity of the samples, while residence time appeared to have little influence over nanoparticle characteristics. Importantly, these experiments showed a narrow set of conditions under which crystalline graphitic nanoparticles were formed. These conditions were correlated with a rotational gas temperature, as estimated through optical emission spectroscopy of the C2 Swan band spectral region, of 970 °C. Nanoparticle characterization under varied synthesis conditions also revealed the dynamic relationship between bond hybridization and surface hydrogen. By selecting conditions that yield the highest quality crystalline graphite nanoparticles, stable photoluminescence from the nanoparticles was observed. These results point to the capability of non-thermal plasmas for controlling not only the functional properties of nanomaterials but also for selective bond hybridization.