Probing Strain and Structural Properties of Catalytic Nanoparticles with Four-Dimensional Scanning Transmission Electron Microscopy

Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM) offers detailed structural insights into nanoparticles by capturing electron diffraction patterns at each scan position, enabling precise strain mapping in both real space (x, y) and diffraction space (kx, ky). In this study, we focus on the structural and strain properties of multi-metallic core@shell catalytic nanoparticles, where the shell is subjected to significant epitaxial strain from the core lattice. These nanoparticles present unique challenges, such as lattice misalignments and projection complexities due to overlapping materials, which we address by applying advanced data processing strategies. Using the exit wave power cepstrum (EWPC) to minimize the effects of small crystal tilts and a decomposition method to separate the contributions of the core and shell, we achieve accurate strain mapping across various shell thicknesses. Our findings highlight strain relaxation pathways within the core@shell architecture, which are critical for understanding and optimizing strain-engineered nanocatalysts. Additionally, we examine nanocrystals with excessive twin boundaries, revealing localized lattice deformations that affect surface strain. This inhomogeneous strain distribution at the twinning boundaries suggests new structural states in nanoparticles, offering insights into their potential catalytic properties and performance.