Influence of Palladium on the Ordering, Final Size, and Composition of Pd–Au Nanoparticle Arrays

Nanostructured substrates exhibiting a regular two-dimensional network of defects represent ideal systems for growing ordered nanoparticle arrays with a narrow size distribution. Here, the growth of Pd–Au nanoparticle arrays on a thin Al2O3 film obtained by oxidation of a Ni3Al(111) single crystal surface has been examined. The nanoparticle composition ranges from pure palladium to almost pure gold with a diameter of ∼2 nm. Small-angle X-ray scattering and X-ray diffraction in grazing incidence (GISAXS and GIXRD) were performed in situ during the sequential deposition of Pd and Au. GISAXS provided evidence of a diffuse scattering contribution whose appearance is linked to the progressive disordering of the arrays. It is correlated to the size of the initial Pd clusters and to the Au/Pd final ratio: the lower the ratio is, the better the organization of the nanoparticle array. More specifically, the arrays start to disorder as soon as one atomic-thick Au layer is deposited on the Pd seeds. The morphologica...