Enhancing Graphene Growth in Carbon Ultrathin Films by Tuning the Ion Kinetic Energy During Film Deposition onto a Catalyst Sublayer

Abstract

A one-step metal-catalyzed process for transforming carbon films into high-quality graphene layers for potential use in various cutting-edge technologies was developed in this study. Carbon ultrathin films grown on CoFe alloy ultrathin sublayers by filtered cathodic vacuum arc using different ion kinetic energies were subjected to thermal annealing at 650 °C for 150 s. X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular dynamics simulations provided insight into phase changes and graphenization at the molecular level. Atomic force microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used to characterize the surface morphology and elemental composition of the C films and the CoFe sublayer before and after thermal annealing. It was found that increasing the C+ ion kinetic energy during C film deposition enhanced graphenization; however, a very high ion kinetic energy had the opposite effect. The sp3/sp2 ratio in the as-deposited C films played a critical role in graphene formation during thermal annealing. Contrary to amorphization, graphenization involved a three-step process encompassing the sequential transformation of high sp3 C to low sp3 C, low sp3 C to graphite, and, last, graphite to nanocrystalline graphite. Variations in the C+ ion kinetic energy indirectly affected the dependence of graphene growth on the hybridization state of the as-deposited C films, the carbon concentration in the CoFe sublayer, and the stability and uniformity of the catalyst CoFe sublayer during thermal annealing, in this manner influencing the overall metal-catalyzed C graphenization process.