Low-temperature phase and morphology transformations in noble metal nanocatalysts

O. Malis, C. Byard, D. Mott, B. N. Wanjala, R. Loukrakpam, J. Luo, C. J. Zhong

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


In situ real-time x-ray diffraction was used to study temperature-induced structural changes of 1-5 nm Au, Pt, and AuPt nanocatalysts supported on silicon substrates. Synchrotron-based x-ray diffraction indicates that the as-synthesized Au and Au64Pt36 nanoparticles have a non-crystalline structure, while the Pt nanoparticles have the expected cubic structure. The nanoparticles undergo dramatic structural changes at temperatures as low as 120 °C. During low-temperature annealing, the Au and AuPt nanoparticles first melt and then immediately coalesce to form 4-5 nm crystalline structures. The Pt nanoparticles also aggregate but with limited intermediate melting. The detailed mechanisms of nucleation and growth, though, are quite different for the three types of nanoparticles. Most interestingly, solidification of high-density AuPt nanoparticles involves an unusual transient morphological transformation that affects only the surface of the particles. AuPt nanoparticles on silicon undergo partial phase segregation only upon annealing at extremely high temperatures (800 °C).

Original languageEnglish
Article number025701
Issue number2
Publication statusPublished - 2011 Jan 14


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