Laser-stepwise-induced graphene with reduced sheet resistance enables electromagnetic shielding manipulation

Laser-induced graphene (LIG) technology enables the direct writing of functional films for flexible devices. However, the intrinsic amorphous structure, triggered by laser-induced ultrafast kinetics, leads to high sheet resistance. Herein, we report a designed laser-stepwise induced graphene (LSIG) method, which sequentially applies focused and defocused laser pulses to polyimide precursors to reduce sheet resistance. In this method, the focused laser pulse induces longitudinal heat penetration and diffusion through the substrate, enabling conversion of polyimide molecules into graphene, while the subsequent defocused pulse facilitates defect healing and crystalline domain growth, achieving a remarkably low sheet resistance of 15 Ω sq⁻¹ for LSIG. The LSIG exhibits a decreased defect density and increased crystalline domain from Raman analysis. Compared with existing approaches involving chemical reduction or high-temperature treatment for LIG optimization, the LSIG methodology accomplishes single-step synthesis while maintaining experimental simplicity. Utilizing LSIG technology, we design and fabricate a flexible frequency-selective surface to demonstrate its potential in electromagnetic devices and systems.