6.3-nm Chalcogenide Lens Could Enable Flexible Displays, Miniaturization

A 6.3-nm-thick metamaterial lens comprising 50-nm-thick gold nanobar arrays may be an ideal candidate for flexible displays and miniature cameras, among other applications. The discovery hinged on the remarkable potential of molybdenum disulphide crystals.

Yuerui Lu (left) and Jiong Yang with their 6.3-nm-thick lens. Courtesy of Stuart Hay/ANU.
"This type of material is the perfect candidate for future flexible displays," said Yuerui Lu, leader of Nano-Electro-Mechanical System Laboratory in the Australian National University (ANU) Research School of Engineering. "We will also be able to use arrays of micro lenses to mimic the compound eyes of insects."

Molybdenum disulphide survives at high temperatures, is a lubricant, a good semiconductor and can emit photons, Lu said. The ability to manipulate light particles on an atomic scale could enable miniaturization of optical components, as well as the integration of advanced optical functionalities.

Molybdenum disulphide is one of the chalcogenide glasses, a class of materials that are being explored for their flexible electronic characteristics.

The ANU team created their lens from a crystal that was 9 atomic layers, which they had peeled off a larger piece of molybdenum disulphide with sticky tape. They then created a 10-μm-radius lens, using a focused ion beam to shave off the layers atom by atom, until they achieved the desired dome shape.

The team reported that 0.7-nm-thick, single layers of molybdenum disulphide had remarkable optical properties, appearing to a light beam to be 50 times thicker, at 38 nm. This property, known as optical path length, determines the phase of the light and governs interference and diffraction of light as it propagates.

To explain the properties, collaborating professor Zongfu Yu at the University of Wisconsin, Madison, developed a simulation and showed that light was bouncing back and forth many times inside the high refractive index crystal layers before passing through.

Molybdenum disulphide crystal's refractive index, the property that quantifies the strength of a material's effect on light, has a high value of 5.5. For comparison, diamond, whose high refractive index causes its sparkle, is only 2.4, and water's refractive index is 1.3.

The research was published in Light: Science and Applications (doi: 10.1038/lsa.2016.46).