Effect of Temperature on AuPd Nanoparticles Produced by Inert Gas Condensation

Bimetallic nanoparticles of AuPd were synthesized using the inert gas condensation technique, where the material is sputtered from a target and the particles are formed in an inert condensation zone. Throughout the synthesis process and jointly with the control of the atmosphere conditions, the region after the condensation chamber was kept at a fixed temperature, and several experimental runs were performed at 700 and 1000 degrees C. The synthesis conditions were set to produce particles of 5 nm of diameter, and almost all of the resulting nanoparticles were icosahedral in shape with small deviations from the mean size. We analyzed the particles by high-angle annular dark field and bright field scanning electron microscopy imaging with a resolution high enough to acquire atomic detail and to measure the distance between planes. From the micrographs and their fast Fourier transform patterns, we found that the lattice detail depends on the thermal treatment with larger lattice fringe displacements in the particles produced at 700 degrees C. Electron energy loss spectroscopy analysis in one and two dimensions shows that irrespective of the temperature the particles keep their icosahedral shape, and both chemical species are distributed nonuniformly all over the volume of the particles, but without forming core-shell structures.