Cs-corrected STEM characterisatioin of Au@Pd Core@Shell nanocubes

Bimetallic (BM) nanoparticles exhibit different properties depending upon the variation of composition and structure. In this work, we report the detailed analysis of core-shell Au-Pd nanocubes obtained by seed mediated growth process, investigated by means of aberration-corrected scanning transmission electron microscopy (STEM), conventional transmission electron microscopy (TEM), tomography 3D reconstruction and strain mapping. Strain mapping and 3D reconstruction showed for the first time that the nanocube is distorted inwards at all faces. The nano-tripod analysis showed the presence of an incomplete FCC layer only in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures. The characterization revealed that nanocubes are formed by concave high index facets of the {410} family with all six faces distorted. The distortion of all faces of nanocube is demonstrated using tomography 3D reconstruction. Detailed analysis of nano-beam electron diffraction (NBD) and high resolution STEM images showed that Pd atoms grow epitaxially on the Au core in both structures. The stability of the nanostructure is provided by the strain. The nano-tripod analysis showed the presence of an incomplete FCC layer in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures.