Computational and experimental studies of solid-state diffusion in bimetallic nanoparticles

Abstract

Metal nanoparticles have attracted considerable attention due to their unique catalytic, optical, magnetic, and electrical properties, particularly in the fields of catalysis, electronics, and medicine. However, detailed characterization via easily accessible and/or historically popular techniques has presented a continuing and complex problem. As such, this work focuses on several escalating computational and experimental X-ray diffraction studies aimed at examining strategies to effectively characterize the diffusional behavior and structural solutions of bimetallic nanoparticles undergoing solid-state diffusion. To increase their applicability, these strategies were developed around relatively popular and robust techniques such as Reverse Monte Carlo, for its use as a structural optimizer, Principal Component Analysis, for its data sub-structure recognition capabilities, and Rietveld Refinement, for its powerful material phase analysis. ☐ The specific objectives of this research were several-fold: (1) to identify the properties of metal pairs that enhance the effectiveness of X-ray diffraction measurements in determining structure, (2) to develop a robust and reproducible procedure for synthesizing bimetallic nanoparticles, and (3) to determine the evolving structure and diffusional behavior of the synthesized nanoparticles samples from (2) during diffusion using X-ray diffraction measurements. ☐ Each of these objectives were achieved to varying degrees. In the first case, the optimal metal pairs were found to have intermediate differences in their lattice parameters and scattering powers via Reverse Monte Carlo simulations. In the second case, a reproducible and relatively robust wet chemistry synthesis recipe for creating bimetallic core/shell nanoparticles was developed utilizing a modified polyol procedure. In the third case, detailed analyses of bimetallic diffusional behavior were successfully conducted using Rietveld Refinement to identify and extract time-resolved structural phases of the synthesized nanoparticles. However, full structural analyses of these same nanoparticles employing RMC were unsuccessful, as their size posed significant computational challenges.