The morphology of metal nanoparticles supported on oxide substrates plays an important role in heterogeneous catalysis and in the nucleation of thin films. For platinum evaporated onto SrTiO3 (0 0 1) and vacuum annealed we find an unexpected growth formation of Pt nanoparticles that aggregate into clusters without coalescence. This hierarchical nanoparticle morphology with an enhanced surface-tovolume ratio for Pt is analyzed by grazing incidence small-angle X-ray scattering (GISAXS), X-ray fluorescence (XRF), atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM). The nanoparticle constituents of the clusters measure 2–4 nm in size and are nearly contiguously spaced where the average edge-to-edge spacing is less than 1 nm. These particles make up the clusters, which are 10–50 nm in diameter and are spaced on the order of 100 nm apart. 2009 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Materials Science and Engineering, Northwestern University, 2220 Campus Dr., Evanston, IL 60208, USA. Tel.: +1 847 491 3570; fax: +1 847 491 7820. E-mail address: email@example.com (M.J. Bedzyk).