Atomic-level insight into sequential evolution of nanocomposite carbon structures in femtosecond laser processing of diamond

Diamond is an exceptional wide-bandgap semiconductor for electronics and quantum technologies. While femtosecond laser processing enables micro/nano fabrication of diamond, the dynamic atomic-level structural evolution during this process remains poorly understood, despite its critical impact on advanced applications. In this work, we investigate the multi-stage structural evolution of diamond under femtosecond laser irradiation, uncovering new scientific findings under laser-induced extreme conditions. The continuous input of pulse energy facilitates the rearrangement of local carbon atoms in the modified layer and partial phase transition layer, transitioning them from thermodynamically unstable to stable states. We introduce a sequential evolution pathway of nanocomposite carbon structures, and reinterpret the phenomenon previously broadly defined as “graphitization”. Specifically, the evolution of diaphite, diamond-OLC (onion-like carbon), and the transition from amorphous carbon to planar-oriented graphite are reported under femtosecond laser surface processing. These phase transitions are initiated by the rapid lattice heating, with their distribution influenced by near-field enhancement effects arisen from surface nanostructures. This work provides atomic-scale insights into diamond's response in femtosecond laser processing, offering a theoretical foundation for ultra-precision micro/nano fabrication of diamond and the development of functional carbon materials.