Insights into the surface responses of graphene oxide irradiated by an infrared femtosecond laser

Graphene oxide (GO) has emerged as unique and multifaceted novel material with a wide range of applications in electrochemistry and optoelectronic engineering. In these applications, GO surface is characterized with different functional structures in the micro-nano scale, while the femtosecond laser is a promising and versatile tool for manufacturing these structures comparing with conventional approaches. However, the comprehensive surface responses and corresponding regimes of GO surface under femtosecond laser irradiation are not yet identified, which creates obstacles to the further application of femtosecond laser in programming GO surface with specific nanopatterns. Herein, theoretical models characterizing the electrical response, i.e., the transient spatial and temporal distribution of infrared femtosecond laser-excited free electron density at the GO surface layers are established. The numerical simulations are carried out using the discontinuous Galerkin finite element algorithm with a 5 fs time step. The relationship between the laser polarized electric field and free electron density is revealed. On this basis, the surface plasma distribution is characterized, the accuracy of which is verified through the comparison of experimental ablation morphology. Thermal, morphological and chemical responses of the GO surface using different parameters are analyzed correspondingly, from which the formation and evolution mechanisms of surface nanopatterns with different features are explained. This work offers a new insight into the fundamental regimes and feasibility of ultrafast patterning of GO for the application of multifunctional device engineering.