Femtosecond Laser-Induced Graphitization of Transparent Cellulose Nanofiber Films

Laser graphitization allows for the spatially targeted modification of biomasses into electrically conductive structures and is a promising technique for the development of sustainable electronic devices. Out of the many biomasses, cellulose nanofiber (CNF) is a sustainable biomass which exhibits unique properties, such as mechanical strength and optical transparency. In this study, we demonstrated the fabrication of highly conductive graphitic carbon from CNFs using a high-repetition femtosecond laser. A conductivity as high as 6.9 S/cm was obtained by single scanning of the laser beam, which is estimated to be more than 100 times higher than the conductivity reported previously. From the Raman analysis of the structure, the formation of highly crystalline graphitic carbon was indicated, which contributes to the high conductivity. In the case of high-repetition femtosecond laser irradiation, it is considered that strong optical effects, in addition to thermal effects, contribute to the degradation of CNFs, resulting in the formation of highly crystalline graphitic carbon. Our presented technique allows for the direct writing of highly conductive graphitic carbon on CNF films, and the development of sustainable electronic devices, using mechanically robust and transparent CNF films as the substrate, should be realized.