Sep 28, 2010
Tuning the size of metal nanoparticles atomic layer by atomic layer
Nanometre-scale particles of metals such as silver or gold, interact with light in very different ways to the bulk material. The difference arises from the way that conduction or 'free' electrons are constrained by the nanoparticle volume. Collective oscillations of these electrons, or 'plasmons', couple with incident electromagnetic light waves scattering them in different ways. This property paves the way for using nanoparticles to harvest light, making solar cells more efficient. It also offers a route to making light-based spectroscopies sensitive to single molecules.
Researchers at the University of Liverpool, UK, have developed a new method of tuning the size of silver nanoparticles using atomic layer deposition (ALD). The technique exposes metal nuclei to pulses of silver-containing molecules in a stepwise manner with pulses of alcohol, so that the nanoparticles grow atomic layer by atomic layer. Collaborators at SAFC Hitech have developed the silver molecules that can deposit silver nanoparticles at temperatures as low as 60 °C.
The team has explored the plasmonic properties of the ALD nanoparticles using high-resolution electron microscopy. The same electron beam used to construct an atomic scale image of a nanoparticle can be used to probe its free electron plasmon distribution. A map of a particular plasmon energy can be constructed by scanning the electron beam across a nanoparticle. A comparison of the map and the electron micrograph provides details of how the shape and size of each nanoparticle confines the plasmon. The method is being used to find out how ALD parameters such as growth temperature and pulse rate influence the growth of silver nanoparticles.
The researchers presented their work in the journal Nanotechnology.
About the author
Paul Chalker is director of the Centre for Materials and Structures in the School of Engineering at the University of Liverpool, UK. His research team focuses on the development of thin film and nanostructured functional materials.