Remote CF₄ Plasma Fluorination of Graphene for Low-Damage Spin-Orbit Engineering

Defect functionalization is a promising route to enhance spin-orbit coupling (SOC) in graphene, but achieving controllable fluorination while suppressing irreversible lattice damage remains challenging. Here we demonstrate low-damage fluorination of monolayer graphene using a remote CF₄ plasma process that suppresses ion-bombardment-induced lattice damage. Raman spectroscopy with defect-activation analysis and an annealing-reversibility test identifies a processing window where fluorination predominantly yields reversible sp³ C-F functionalization while minimizing vacancy formation. Nonlocal transport measurements show that the nonlocal resistance increases in fluorinated graphene and decays exponentially with channel length, consistent with spin diffusion and yielding a spin relaxation length of ∼0.4 μm. Within the Elliott-Yafet framework, we estimate an effective SOC energy scale of 4-9 meV. These results provide a Raman-validated, tunable process route for enhancing SOC in graphene while suppressing vacancy damage.