Researchers Use Highly Conductive Gold Nanoparticle to Develop World’s Tiniest Optical Cavity

Light has been concentrated down to smaller than a single atom by researchers with the help of the strange properties of tiny particles of gold, allowing them to observe individual chemical bonds inside molecules, and making room for new ways to study matter and light.

For hundreds of years scientists believed that light like all waves cannot be focused down smaller than its wavelength just below a millionth of a meter. Researchers from the University of Cambridge have recently developed the world’s smallest magnifying glass, capable of focusing light a billion times more tightly, down to the scale of single atoms.

The team, in collaboration with European colleagues used highly conductive gold nanoparticles in order to make the world’s tiniest optical cavity, so small that it only allows a single molecule to fit within it.

This cavity, referred by the researchers as a ‘pico-cavity’, consists of a bump in a gold nanostructure the size of one atom, and restricts light to less than a billionth of a meter. The journal Science reported the results, which provide new ways to study the interaction of matter and light, including the potential of allowing molecules in the cavity to go through new types of chemical reactions, for the development of entirely different types of sensors.

Developing nanostructures with a single atom was a highly challenging task according to the researchers. “We had to cool our samples to -260°C in order to freeze the scurrying gold atoms,” said Felix Benz, lead author of the study. In order to build the pico-cavities and observe real-time single atom movement the researchers shone laser light on the sample.

“Our models suggested that individual atoms sticking out might act as tiny lightning rods, but focusing light instead of electricity,” said Professor Javier Aizpurua from the Center for Materials Physics in San Sebastian in Spain, who headed the theoretical section of this research.

Even single gold atoms behave just like tiny metallic ball bearings in our experiments, with conducting electrons roaming around, which is very different from their quantum life where electrons are bound to their nucleus.

Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laborator

The findings prove the possibility of opening a completely new field of light-catalyzed chemical reactions, allowing complex molecules to be developed from smaller components. In addition, there is also the possibility to develop new opto-mechanical data storage devices, allowing information to be stored in the form of molecular vibrations and written and read by light.

The research is financially aided as part of an investment by UK Engineering and Physical Sciences Research Council (EPSRC) in the Cambridge NanoPhotonics Centre, as well as the European Research Council (ERC) and the Winton Programme for the Physics of Sustainability. The research was supported by the Spanish Council for Research (CSIC) and the University of the Basque Country (UPV/EHU).