AgNiCoCr Nanoparticles: Exploring the Morphological Shift from Elementally Segregated to High Entropy Structures.

Controlling elemental mixing in nanoparticles composed of immiscible elements remains a central challenge in high-entropy materials design. Here, we demonstrate a kinetic pathway that enables a transition from elementally segregated to high-entropy AgNiCoCr nanoparticles using nanosecond laser-induced dewetting of metallic thin films. During this nonequilibrium process, nanoparticles form through a sequence of morphological transformations and ultimately evolve into near-spherical structures with thickness-dependent sizes. In the chosen model system, Ag is thermodynamically immiscible with Ni and Co, whereas Ni, Co, and Cr are mutually miscible at equiatomic compositions. By varying the thickness and configuration of the metallic thin-film layers, the liquid-phase lifetime during laser irradiation is systematically tuned, thereby regulating mass transport and solidification dynamics. Ultrathin film stacks produce smaller nanoparticles (up to ∼40 nm) that rapidly solidify on nanosecond time scales, kinetically trapping metal atoms into a chemically disordered high-entropy phase. In contrast, thicker films remain molten for longer durations during dewetting, leading to the formation of larger nanoparticles with pronounced elemental segregation into AgNiCoCr core-shell or Janus structures. Supported by atomistic simulations, this work demonstrates that solidification kinetics, rather than thermodynamic immiscibility, governs chemical order in laser-processed nanoparticles, providing a versatile strategy for engineering high-entropy nanoparticles from immiscible elements.