Defocused Laser-Induced Anisotropic Freestanding Graphene Architectures

We report the intrinsic structural anisotropy in freestanding laser-induced graphene (FLIG) sheets produced through controlled laser defocusing of a CO2 pulse laser on polyimide. Defocusing enlarges the laser spots, enabling uniform carbonization and spontaneous substrate detachment without postprocessing, resulting in 3D-FLIG structures (∼29 μm thick) and over 90% carbon content. Angle-resolved Raman spectroscopy shows significant in-plane anisotropy in FLIG sheets and LIG needles (p < 0.0001), contrasting with isotropic embedded LIG, due to strain-induced symmetry breaking and preferred lattice alignment. Laser defocusing offers a scalable way to engineer microlevel directional anisotropy in freestanding graphene for potential electronic and thermal devices.