The two main types of particle-based semiconductors already in use are colloidal quantum dots and organic semiconductors. These materials are at the nanoscale. Their tiny size means they are subject to a phenomenon known as quantum confinement, which causes changes to their optical and electronic properties. These changes make them suitable for their intended applications.
Metal nanoclusters combine aspects of both these other materials. Like colloidal quantum dots, they are very stable. Like organic semiconductors, they are atomically precise, or molecular, containing a specific number of atoms in their metallic core.
However, despite containing all the right ingredients, metal nanoclusters had never before been shown to display semiconducting properties.
The team devised a way of making films of nanoclusters consisting of 25 gold atoms (Au25). They then observed that the nanoclusters displayed semiconducting properties. Specifically, they observed field effect and photoconductivity in phototransistors made of these films. These unique properties are hallmarks of all semiconducting materials.
"The discovery of semiconducting properties in metal nanoclusters could pave the way for a variety of new applications, from field effect transistors and photodetectors to light emitting diodes and solar cells," explained Professor Christian Klinke of Swansea University.
"These devices could be manufactured on flexible bases. Many metal nanoclusters, including the ones we investigated in this report, have almost infinite stability, which could make them suitable for ink-jet printing applications."
He concluded, "We need to build on this finding and refine the technique further. But this discovery points the way ahead. It shows that we can use metal nanoclusters to produce high quality semiconducting films that are easy to assemble."
