EXTENDED ABSTRACT: The emerging potential of polyelemental nanoparticles in diverse fields has led to an increased demand for combinatorial and high-throughput synthesis of nanoparticles that encompass an enormous compositional and structural parameter space [1,2]. Here, we report a probe-based nanoreactor-mediated method to synthesize polyelemental nanoparticles in a site-specific manner. The method allows one to create nanoparticles consisting of all combinations of desired elements. Important insights into the factors that lead to alloy formation and phase-segregation in polyelemental nanoparticles were obtained, and design rules for engineering heterostructures in a single nanoparticle were established. Further, when the method was combined with massively parallel printing techniques, combinatorial libraries of nanoparticles can be made over large areas, providing a powerful platform to screen polyelemental nanoparticles in a systematic fashion. Based on the synthetic capability, we have systematically investigated the thermodynamic phase behavior of immiscible elements in nanoparticles using Au-Rh as a model system. Our results show that their miscibility is increased in nanoparticles by forming solute clusters and single atoms in the particle matrix [3-5]. The two immiscible elements eventually exhibit a phase separation-to-alloy transition in particles with decreased size and become completely miscible in sub-2 nm particles across the entire compositional range. The inverse phase behavior is mainly dictated by the particle size, particle composition, and possible surface adsorbates, highlighting the substantial discrepancy between the bulk and nano- materials. Collectively, our work not only advances the understanding of the nanoscale thermodynamics of polyelemental materials, but also provides important guidelines for the design of alloy and phase-separated nanostructures that can be useful for catalysis, plasmonics, and other applications.
Keywords：polyelemental nanoparticles; phase behavior; thermodynamics
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