ABSTRACT
Nanoparticles are usually considered to have at least one dimension less than 100 nm, although this denition is not rigid. Such particles have a larger surface area-to-volume ratio than larger particles, affecting the way that they react with other particles and with each other. A 10 nm diameter nanoparticle has about 15% of the atoms on their surface, and by comparison, this drops to <1% for a bulk solid. Because a particle may only consist of a few atoms, the energy levels associated with extended solids such as bands in metals no longer apply, and the electronic energy levels are more similar to the quantised levels found in individual atoms. This affects their conductivity and the way that they interact with light and other forms of energy.
