US researchers have found a way to study defects on surfaces of nanoparticles, which are thought to be critical for catalytic activity.

Metal nanoparticles are the key to the activity of many catalysts, including those in car catalytic converters. To improve these catalysts it is important to know what is happening at the atomic level. Miguel José-Yacamán and colleagues at the University of Texas at Austin have found that, using microscopy and computer modelling, they can obtain much more detail than before about nanoparticle surface defects.

José-Yacamán's method uses aberration-corrected TEM (transmission electron microscopy), which uses software to correct distortions introduced by the microscope lenses. This enables imaging of atoms in non-regular environments (such as at surface defects), which is not possible with regular TEM. The team applied this technique to a gold-palladium nanoparticle, and not only found that it was a single crystal, but that it consisted of three distinct spherical layers, each with a different ratio of the two metals. They also obtained electron density profiles along different axes through the particle. By comparing these with computer models, they found that the nanoparticle contains steps, edges and kinks on its surface.

José-Yacamán says their results show that 'the surface of the particle is rather rough at the atomic scale.' He adds that it is very likely that the stepped surface of these nanoparticles plays an important role in their catalytic activity.

David Cockayne, professor of materials chemistry at the University of Oxford, UK, is enthusiastic about the work, saying that it 'demonstrates the enormous potential for modern aberration-corrected TEM to explore the complex and technologically important structures of nanoparticles.' Luis Liz-Marzàn, an expert in nanoparticles from the University of Vigo in Spain, echoed these thoughts, saying this 'represents a leap in electron microscopy capabilities for nanoparticle analysis.'

David Barden