Laser Generation of AlCrCuFeNi High-Entropy Alloy Nanocolloids

We report on the synthesis of AlCrCuFeNi high-entropy alloy (HEA) nanoparticles (NPs) using pulsed laser ablation of the AlCrCuFeNi target in two different solvents, deionized water (DIW) and anhydrous ethanol (EtOH). The laser-generated AlCrCuFeNi HEA NPs in DIW and EtOH show a bimodal size distribution of the NPs. The compositional, phase, and structural analysis using microscopic and spectroscopic techniques reveals the formation of different phases and nanostructures of AlCrCuFeNi NPs in these solvents. In DIW, the formation of a core–shell structure in which the shell is rich in Al and O and the core is rich in Cu–Ni was observed. However, in EtOH, the formation of solid solution AlCrCuFeNi HEA NPs was observed. The scanning transmission electron microscopy–EDS analysis revealed that the segregation of Al is driven by the formation of an oxide. The statistical analysis of the chemical composition of the particles revealed the different trends as a function of particle size. Larger NPs show variation in their composition, and the content of O plays a crucial role in the phase segregation of HEA NPs, leading to compositional variation in the oxide layer and the core of the HEA NPs. However, in small NPs, the homogeneous variation of all the elements in HEA was observed. Further, the calculation of physiochemical and thermodynamic parameters indicates the formation of a solid solution with a mixture of face-centered cubic and body-centered cubic phases in HEA NPs. Based on the experimental results, a possible growth mechanism of different morphologies and phases of these NPs during pulsed laser ablation in liquid is discussed.