Advanced STEM microanalysis of bimetallic nanoparticle catalysts.

Individual particles within bimetallic nanoparticle populations are not always identical, limiting the usefulness of bulk analysis techniques such as EXAFS. The scanning transmission electron microscope (STEM) is the only instrument able to characterize supported nanoparticle populations on a particle-by-particle basis. Quantitative elemental analyses of sub-5-nm particles reveal phase separations among particles and surface segregation within particles. This knowledge can lead to improvements in bimetallic catalysts. Advanced STEMs with field-emission guns, aberration-corrected optics, and efficient signal detection systems allow analysis of sub-nanometer particles. [ABSTRACT FROM AUTHOR]