3D Reconstruction of the Alloying Process of AuAg Nanoparticles by Small Angle X-Ray Scattering

The element distribution pattern in a bimetallic nanoparticle system is usually varying during the synthesis, post-processing, and catalysis reactions under operando conditions. The structural complexity of the nanoparticle system brings significant difficulty in determining the relationship between the structures and their physical and chemical properties. Small angle x-ray scattering (SAXS) can be used to characterize size, morphology, and density of a nanoparticle system under operando conditions. We applied SAXS on monodispersed core-shell AuAg nanoparticle system to monitor the growth of Au layers on Ag nanoparticles and the following alloying process when the nanoparticles are heated. The nanoparticle density distribution change caused by the diffusion of Au and Ag atoms is reconstructed by DENsity from Solution Scattering (DENSS) algorithm with a sub-nanometer resolution. The time-resolved series of 3D images enables the quantitative study of the 3D evolution of size, morphology, composition, and element distribution of the alloying AuAg nanoparticle system. The density contrast SAXS imaging protocol established in this work provides a transformative way to "see inside" nanoparticle structure other than the traditional electron microscopic methods.