Laser Annealing of Fluorine-Doped Graphene Enables Precise Wettability Control and Its Application in Integrated Microcapacitors

Graphene films with tunable wettability exhibit great potential in energy storage, sensing, and microfluidics. However, achieving precise control over their hydrophilic/hydrophobic properties remains a critical challenge. Herein, we develop a two-step laser processing method for ambient-air fabrication of fluorine-doped graphene (F-LIG) films with tunable wettability. The method involves picosecond UV laser pyrolysis of fluorinated ethylene propylene (FEP)/polyimide (PI) films followed by CO₂ laser annealing of the resultant F-LIG films. The formation mechanisms were clarified through microstructure and chemical characterizations and molecular dynamics simulation. Results demonstrate that the UV laser induces a transient high-temperature/pressure environment at the FEP/PI interface, facilitating fluorine diffusion and C-F covalent bonding to yield superhydrophobic F-LIG. Subsequent laser annealing reconstructs the carbon lattice, removes unstable fluorine residues, regulates oxygen-containing groups, and constructs through-pores. This annealing process achieves nearly linear wettability tuning from superhydrophobicity (160.2°) to near-superhydrophilicity (15.4°) by modulating surface energy. Moreover, the near-superhydrophilic F-LIG demonstrates excellent conductivity and capacitive performance (8.9 mF/cm²) in microcapacitors, enabling integrated applications. Significantly, all integrated microcapacitors spanning 1 to 30 cells maintain excellent performance consistency and scalable series-parallel performance. This work provides an approach for the efficient processing of graphene with on-demand wettability engineering and monolithic integration of energy storage.