Pulse Duration Dependence of Novel Metal Alloying on Fe/Cr/Ni Thin Films by Ultra-Short Pulsed Laser Irradiation

We examined the possibility of suppressing elemental segregation of high-entropy alloys (HEAs) using femtosecond laser irradiation. Thin films of iron (Fe), chromium (Cr), and nickel (Ni) were deposited on the surfaces of n-type SiC and p-type GaN substrates. The thicknesses of the Fe, Cr, and Ni films were 12, 7, and 11 nm, respectively. Laser irradiation was performed from the substrate side by focusing on the interface between the Fe film and substrate. Scanning transmission electron microscopy (STEM) bright-field images superimposed on the elemental maps of Fe, Cr, and Ni showed a more homogenous mixing of Fe, Cr, and Ni in the femtosecond-laser-modified region than in the picosecond-laser-modified region. In particular, the Ni distribution showed a significant improvement in homogeneity. In other words, the Ni mixture was more homogeneous in the femtosecond laser-modified region than in the picosecond laser-modified region. Although the duration of the picosecond laser pulse was sufficiently long for atomic diffusion, segregation still occurred during the cooling process following laser irradiation

Pulse Duration Dependence of Novel Metal Alloying on Fe/Cr/Ni Thin Films by Ultra-Short Pulsed Laser Irradiation

We examined the possibility of suppressing elemental segregation of high-entropy alloys (HEAs) using femtosecond laser irradiation. Thin films of iron (Fe), chromium (Cr), and nickel (Ni) were deposited on the surfaces of n-type SiC and p-type GaN substrates. The thicknesses of the Fe, Cr, and Ni films were 12, 7, and 11 nm, respectively. Laser irradiation was performed from the substrate side by focusing on the interface between the Fe film and substrate. Scanning transmission electron microscopy (STEM) bright-field images superimposed on the elemental maps of Fe, Cr, and Ni showed a more homogenous mixing of Fe, Cr, and Ni in the femtosecond-laser-modified region than in the picosecond-laser-modified region. In particular, the Ni distribution showed a significant improvement in homogeneity. In other words, the Ni mixture was more homogeneous in the femtosecond laser-modified region than in the picosecond laser-modified region. Although the duration of the picosecond laser pulse was sufficiently long for atomic diffusion, segregation still occurred during the cooling process following laser irradiation

Morphology and structure of diamond-like carbon film induced by picosecond laser ablation

Raman spectroscopy was performed to investigate the laser-induced microscopic structural changes in diamond-like carbon known as tetrahedral amorphous carbon. Coarse laser-induced periodic surface structures (LIPSSs) at the center of the crater and fine LIPSSs at the upper and lower peripheral regions of the ablated crater were formed via laser irradiation. An analysis of the Raman spectra via mapping measurements around the periphery of the crater demonstrated an increase in defect density occurred without morphological or structural changes. In irradiated areas with a higher local fluence, clustering and crystallization of sp2 occurred. The relationship between the crystalline structural changes and the local fluence was discussed

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