Tuning atomic structure of single-crystalline diamond surfaces by femtosecond laser for enhanced heat transfer

Diamond offers exceptional thermal conductivity for high-power and wide-bandgap devices, but poor wettability limits its application in liquid-cooling environments. In this work, femtosecond laser irradiation was used to modify the near-surface structure of single-crystal diamond, and the resulting effects on bonding configuration, lattice integrity, thermal response, and wetting behavior were systematically examined. Laser processing roughens the surface, produces an amorphous carbon layer, and introduces shock-related stress into the substrate. As the fluence increases from 3.77 to 19.39 J/cm², the amorphous layer becomes thinner and less ordered, the amorphous–diamond interface becomes progressively more corrugated, and the underlying crystal evolves from exhibiting residual strain to containing dense stacking faults and point defects. The roughened surfaces and laser-induced sp²-bonded amorphous carbon improve wettability and facilitate bubble nucleation during boiling, while ultrafast reflectivity measurements show that defect accumulation suppresses carrier excitation and slows thermal relaxation. In line with these trends, the droplet evaporation time decreases from 8.357 s on the pristine surface to 6.745 s after irradiation at 3.77 J/cm², whereas the times for the 7.97 and 19.39 J/cm² surfaces increase to 6.935 and 7.890 s, respectively. These results demonstrate how laser-induced carbon structural modifications govern thermal transport and identify processing conditions that enhance wettability without severely degrading thermal transport performance, offering a promising route for engineering diamond interfaces for liquid-cooling applications.