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Analytical Chemistry

Imaging Pinpoints Nanoparticle Atoms

Combining TEM and computer simulations provides an intimate analysis of bimetallic cluster catalysts

by Mitch Jacoby
November 29, 2010 | A version of this story appeared in Volume 88, Issue 48

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Credit: Volkan Ortalan
Tall peaks in this TEM-derived plot correspond to a few-atoms-thick region of a Rh-Ir nanoparticle.
Credit: Volkan Ortalan
Tall peaks in this TEM-derived plot correspond to a few-atoms-thick region of a Rh-Ir nanoparticle.

An analytical technique combining transmission electron microscopy (TEM) and computational image analysis can determine the three-dimensional structures of nanosized bimetallic clusters and the positions of the individual atoms, according to researchers at the University of California, Davis (Nat. Nanotechnol., DOI: 10.1038/nnano.2010.234). Metallic nanoparticles play key roles in heterogeneous catalysis, including petroleum refining and automotive emissions cleanup. Bimetallic and multicomponent nanoparticles are often more active catalysts than single-metal nanoparticles, but the catalytic function of each component is often unknown. Determining the atomic structure of such particles could help reveal that information and lead to improved catalysts. Volkan Ortalan, Bruce C. Gates, and coworkers at UC Davis applied their technique, which uses a TEM method that’s sensitive to the specimen atoms’ atomic numbers, to analyzing rhodium-iridium clusters. The team identified the 3-D shapes of the clusters and determined the positions and chemical identity of each of the atoms. The researchers then tracked changes in the positions of the metal atoms in sequential image frames.

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