World’s Smallest Magnifying Glass

Principle of single-molecule optomechanics in “picocavities”. (Source: NanoPhotonics Cambridge / B. deNijs)

Principle of single-molecule optomechanics in “picocavities”. (Source: NanoPhotonics Cambridge / B. deNijs)

For centuries, scientists believed that light, like all waves, couldn’t be focused down smaller than its wave­length, just under a millionth of a metre. Now, researchers led by the University of Cambridge have created the world’s smallest magni­fying glass, which focuses light a billion times more tightly, down to the scale of single atoms.

In colla­boration with colleagues from Spain, the team used highly conductive gold nano­particles to make the world’s tiniest optical cavity, so small that only a single molecule can fit within it. The pico-cavity consists of a bump in a gold nano­structure the size of a single atom, and confines light to less than a billionth of a metre. The results open up new ways to study the interaction of light and matter, including the possi­bility of making the molecules in the cavity undergo new sorts of chemical reactions, which could enable the deve­lopment of entirely new types of sensors.

According to the researchers, building nano­structures with single atom control was extremely chal­lenging. “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. The researchers shone laser light on the sample to build the pico-cavities, allowing them to watch single atom movement in real time. “Our models suggested that indi­vidual atoms sticking out might act as tiny lightning rods, but focusing light instead of elec­tricity,” said Javier Aizpurua from the Center for Materials Physics in San Sebastian, who led the theo­retical section of this work.

“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,” said Jeremy Baumberg of the Nano­Photonics Centre at Cambridge’s Cavendish Labo­ratory, who led the research. The findings have the potential to open a whole new field of light-catalysed chemical reactions, allowing complex molecules to be built from smaller components. Additionally, there is the possi­bility of new opto-mechanical data storage devices, allowing infor­mation to be written and read by light and stored in the form of molecular vibrations. (Source: U Cambridge)

Reference: F. Benz et al.: Single-molecule optomechanics in “picocavities”, Science 354, 725 (2016); DOI: 10.1126/science.aah5243

Links: NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, UK • Donostia International Physics Center, San Sebastián, Spain

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