TEM studies of stress relaxation in catalytic Au-Pd core-shell nanoparticles

Transmission electron microscopy and diffraction are used to measure the lattice strain in catalytic Au-Pd core-shell nanoparticles. In order to simplify analysis, single nanoparticles were oriented to achieve strong two-beam diffracting conditions from the nanoparticle centre, such that diffraction was sensitive to the strain parallel to the Au-Pd interface. Corresponding selected area diffraction patterns were used to measure the in-plane strain as a function of the Pd thickness, which is shown to follow the equilibrium (Matthews) theory. These results suggest that, contrary to expectation, strain is not an important factor accounting for the difference in catalytic activity between nanoparticles and thin films. The significance of these results is discussed.