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 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 morphological parameters of the ordered nanoparticles were obtained from GISAXS and complemented by structural information derived from GIXRD. This study provides new insights into the link between the size and the composition of these bimetallic nanoparticles for synthesizing ordered arrays. Such tailored samples might then be used as model catalytic systems for further operando studies.