Study of Au–Pd core–shell nanoparticles by using slow positron beam

Binary Au–Pd nanoparticles were synthesized by ultrasonic irradiation of solutions containing Au3+ and Pd2+ ions (the ion ratio from 0.3:0.7 to 0.9:0.1 mM) and cationic surfactant (SDS: sodium dodecyl sulfate). In each case the core–shell structure (Au core, Pd shell) was confirmed by scanning transmission electron microscopy (STEM). The mean diameters of them were all about 9 nm, and the thickness of the Pd shell depends on the ratio of Pd2+ and Au3+ ions in solution. In order to study the electronic states of core–shell nanoparticles and their dependence on shell thickness, Doppler broadening measurements were performed for Au–Pd core–shell nanoparticles by using slow positron beam technique. The ratio curves of Au–Pd particles did not match with those of pure Pd and pure Au, but a small difference in the low electron momentum region was observed among nanoparticles depending on Pd shell thickness.