Au(core)/Pd(shell) structures analyzed by high-resolution medium energy ion scattering

Bimetallic nano-particles taking a core/shell structure dispersed on metal-oxide supports work more efficiently than the mono-metallic ones as heterogeneous catalyst. In order to elucidate the high catalytic activities, it is essential to analyze quantitatively the size and structure of the core/shell particles. Here, we demonstrate that high-resolution medium energy ion scattering (MEIS) spectrometry makes it possible to identify growth of bimetallic core/shell nano-particles and also to determine the average size of core and shell, respectively, together with the size distribution with an accuracy better than 0.1 nm. As an example, Au(core)/Pd(shell) particles with a nominal size (outer diameter) of 2.4 and 3.7 nm prepared by an alcohol reduction technique were analyzed using 120 keV He+ ions. The present analysis clearly showed formation of Au(core)/Pd(shell) structures with almost the same radii as those expected from the chemical preparation condition. Growth of Au/Pd alloyed particles and significant inclusion of Au and Pd mono-metallic particles were ruled out.