HAADF study of Au-Pt core-shell bimetallic nanoparticles

Bimetallic Pt/Au nanoparticles have been synthesized by the polyol method, stabilized by poly (vinylpyrrolidone) (PVP). The structure of the particles has been determined using transmission electron microscopy and a HAADF (High Angle Annular Dark Field) technique. Some particles present a core-shell structure, with a contrast not predicted by simple atomic number contrast (approximate to Z(2)). Strain fields present in the core-shell interface are thought to be the cause of this contrast, which depends on the orientation of the particle with respect to the electron beam. We propose HAADF as a useful technique to identified core-shell structures in nanoparticle systems.