Direct visualisation, by aberration-corrected electron microscopy, of the crystallisation of bimetallic nanoparticle catalysts.

Using a scanning transmission electron microscope, corrected for aberration, ultra-high resolution images of the internal structure of nanoparticle clusters, as well as the number of atoms present per cluster, may be directly determined: it is shown that individual bimetallic clusters of Ru10Pt2 have a "molecular" structure and that when they coalesce into larger entities containing ca. 200 atoms they adopt the regular crystalline, and facetted, state of a bulk metal.