Fig. 1. Copper microstructure sheet resistance change curve with laser power (inset: photograph of the LED circuit prepared from Cu microstructure)

Fig. 2. XRD pattern of copper microstructure prepared with different laser powers

Fig. 3. SEM images of copper microstructure obtained under different laser power(insets: high-resolution SEM images). (a) 322 mW; (b) 626 mW;(c) 960 mW; (d) 1240 mW; (e) 1690 mW;(f) 1880 mW

Fig. 4. HRTEM images of the copper microstructure obtained at 960 mW laser power. (a) Cu nanoparticles; (b) interfaces of Cu nanoparticles and Cu-C structure; (c) (d) interfaces of Cu-Cu₂O nanoparticles

Fig. 5. COMSOL simulation results of femtosecond laser irradiation of a Cu nanoparticle dimer. (a) Schematic of the model geometry for a Cu nanoparticles dimer; (b) relative electric field enhancement (|E/E₀|) distribution of the Cu nanoparticle dimer under 960 mW laser irradiation, where E is the calculated electric field intensity and E₀ is the incident electric field intensity; (c)--(e) temperature field distribution of a Cu nanoparticle dimer under 322 mW, 960 mW, and 1690 mW single pulse laser irradiation after 5 ps, respectively

Fig. 6. Relationship between electron and lattice temperature of Cu nanoparticles in the first 5 ps under different laser powers of single pulse laser irradiation