Aberration Corrected Electron Microscopy Study of Bimetallic Pd–Pt Nanocrystal: Core–Shell Cubic and Core–Frame Concave Structures

Pd–Pt core–shell/frame bimetallic nanocrystal has attracted great interest in the applications of catalysis, plasmonics, and electronics. Controlling the shape, morphology, and chemistry of the outer Pt layer has been widely accepted as a critical factor to the realization of these applications. In this study, we provide a comprehensive study on the atomic structures, composition distribution, and 3D morphology of the shell layer in the bimetallic Pd–Pt nanocrystal with core–shell cubic and core–frame concave structures by using aberration-corrected high angle angular dark field–scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron tomography. The structure and chemistry characteristics of the shell layer in the core–shell cubic and core–frame concave Pd–Pt nanocrystals have been investigated at the atomic scale to reveal the deposition and growth mechanism of Pt adatoms on to Pd cubic seeds under various conditions. In core–shell Pd–Pt cubic nanocrystals, the most outset surface Pt layer is not fully covered, while the interfacial layer is a mixed Pt and Pd layer at the atomic scale due to the termination of growth steps under a two-dimensional growth mechanism. 3D electron tomography confirmed that the Pd–Pt core–frame concave nanocrystal has high index crystallography planes at the surfaces. The characterization methodology developed in this study provides important insights that will guide the analyses of catalytic, plasmonic, and electronic properties relevant to nano and atomic structures and the design of Pd–Pt nanocrystals.