Octahedral Growth of PtPd Nanocrystals

PtPd nanoparticles are among the most widely studied nanoscale systems, mainly becauseof their applications as catalysts in chemical reactions. In this work, a combined experimental-theoretical study is presented about the dependence of growth shape of PtPd alloy nanocrystals ontheir composition. The particles are grown in the gas phase and characterized by STEM-HRTEM.PtPd nanoalloys present a bimodal size distribution. The size of the larger population can be tunedbetween 3.8±0.4 and 14.1±2.0 nm by controlling the deposition parameters. A strong dependenceof the particle shape on the composition is found: Pd-rich nanocrystals present more roundedshapes whereas Pt-rich ones exhibit sharp tips. Molecular dynamics simulations and excess energycalculations show that the growth structures are out of equilibrium. The growth simulations areable to follow the growth shape evolution and growth pathways at the atomic level, reproducing thestructures in good agreement with the experimental results. Finally the optical absorption propertiesare calculated for PtPd nanoalloys of the same shapes and sizes grown in our experiments.