Finite Element Modeling of Scanning Speed Effects in Femtosecond Laser-Induced Graphene Fabrication
Abstract
Laser-induced graphene (LIG) enables mask free direct writing of conductive carbon structures on polyimide substrates for flexible electronic and sensing applications. In femtosecond laser-induced graphene (FLIG), the scanning speed strongly affects the local temperature field, and thus the extent and quality of graphitization, but this dependence is still not fully quantified. In this study, a time dependent finite element model is implemented in COMSOL Multiphysics to resolve the temperature distribution generated by a femtosecond laser beam on a polyimide surface as a function of scanning speed. The laser is described as a moving Gaussian surface heat source, and the transient heat conduction equation is solved to capture ultrafast heating and cooling during a pulse train. Simulations for scan speeds between 0.05 and 0.20 m/s show that decreasing the speed increases the peak temperature and enlarges the heat affected zone, whereas higher speeds reduce both quantities. By comparison of the predicted peak temperatures with the graphitization thresholds in the literature for polyimide derived graphene, an intermediate scan speed window is identified in which the thermal budget is sufficient for graphene formation while avoiding excessive overheating and damage. This modeling framework provides a practical tool for pre selecting femtosecond laser parameters and for accelerating the optimization of FLIG processes for flexible graphene based devices.