Quenching high-temperature phase in Cu–Sn alloy system by femtosecond and picosecond laser irradiation

This study investigated the dependence of irradiation fluence and pulse duration on the non–thermal alloying of Cu and Sn through laser irradiation. Femtosecond and picosecond laser irradiation were applied to the GaN part of a bilayer of Cu and Sn deposited on GaN. The laser beam operated at a wavelength and repetition rate of 1030 nm and 1 MHz, respectively, with pulse durations of 0.65 and 38 ps. Subsequently, the irradiated samples were thinned using a focused ion beam, and the cross-sections were examined with transmission electron microscopy. The lattice constants of the resultant phases were identified from selected area diffraction patterns. In data analysis, we identified the phases as β-Sn and ε-phases first, if discernible within a 5% error margin, employing high-temperature phases when identification was not possible. In the irradiated area, only Cu and Sn were detected under a lower fluence and shorter pulse duration. However, δ-phases, which are alloys of Cu and Sn, formed at relatively higher fluences and longer pulse durations. This high-temperature phase, unique to picosecond laser irradiation, cannot be obtained through conventional thermodynamic processes, highlighting the unique capabilities of laser-induced processing in creating novel alloy phases. These findings advance our understanding of laser-material interactions and provides a foundation for developing advanced materials with tailored properties for various applications.