Credit: © 2008 APS

Nanoparticles can have strikingly different properties depending on their size, so it is important to have effective ways of measuring them. Ziyou Li and colleagues1 at the University of Birmingham have developed mass standards that could provide a quick and easy way of weighing nanoparticles and gaining insight into their fine structure.

The researchers previously developed a way of accurately estimating the mass of nanoparticles fired in a beam, by measuring their time-of-flight. They used this mass-selection technique to deposit several clusters of gold, with known numbers of atoms, onto graphite substrates.

The nanoclusters were observed using a scanning-transmission electron microscope in high-angle annular-dark-field (HAADF) mode. The team found that the HAADF intensity of a cluster was monotonically dependent on the cluster size. This provided a calibration curve for 'weighing' other gold nanoparticles by measuring the HAADF intensity, and was tested on gold particles from both colloidal suspensions and thermal sublimation.

Once researchers know both the mass and size of a nanoparticle, they can get an idea of its shape and structure. This new technique could be especially important for industrial catalysts, whose performance is dependent on particles having complex shapes with a large surface area.