Nuclear magnetic resonance has revealed molecules hopping around on the surface of nanoparticles. 

Researchers in Canada used solid state nuclear magnetic resonance (NMR) to study the composition of cadmium-based nanoparticles. The researchers were surprised to find that molecules coating the particles were actively hopping around on the surface. 

Christopher Ratcliffe and colleagues at the Steacie Institute for Molecular Sciences, Ottawa, Ontario, looked at nanoparticles grown in an organo-phosphorous solution, whose surfaces were coated with organo-phosphorous molecules. The ¹³C NMR spectra of the particles showed that the organo-phosphorous molecules jumped around from one site to another on the particle surface, indicating that the molecules are only loosely attached to the particle.

The researchers were also able to glean information about the structure and composition of different particle types, such as alloys and layered particles, using ¹¹³Cd, ⁷⁷Se, and ³¹P NMR. 'The complete characterization of the composition and structure of nanoparticles is notoriously difficult, and it is necessary to use numerous techniques which provide different pieces of information to build up a consistent picture,' said Ratcliffe. 'Solid state NMR is providing important new information about cadmium chalcogenide nanoparticles that could not be obtained in other ways, adding new pieces to the overall picture.' 

Ratcliffe said, 'solid state NMR is a vital tool in the arsenal of characterisation techniques available for nanomaterials.' 

Mark Smith, professor of physics at the University of Warwick, UK, agreed. 'This research demonstrates the importance of the technique for understanding the atomic architecture of materials,' he said. 

Emma Lawrence