Larry Lu (left) and Jiong Yang (right) with the lens shown on screen. Image: Stuart Hay, ANU.
Larry Lu (left) and Jiong Yang (right) with the lens shown on screen. Image: Stuart Hay, ANU.

Scientists have created the world's thinnest lens, just one two-thousandth the thickness of a human hair, opening the door to flexible computer displays and a revolution in miniature cameras.

Lead researcher Yuerui (Larry) Lu from the Australian National University (ANU) in Canberra said the discovery hinged on the remarkable potential of molybdenum disulphide. Molybdenum disulphide belongs to a class of materials known as chalcogenide glasses, which possess flexible electronic characteristics that have made them popular for use in high-technology components.

"This type of material is the perfect candidate for future flexible displays," said Lu, leader of the Nano-Electro-Mechanical System (NEMS) Laboratory in the 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 is an amazing crystal," he added. "It survives at high temperatures, is a lubricant, a good semiconductor and can emit photons too. The capability of manipulating the flow of light in atomic scale opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities."

Lu's team created their lens from a crystal 6.3nm thick – comprising just nine atomic layers – which they had peeled off a larger piece of molybdenum disulphide with sticky tape. They then created a lens with a radius of 10µm, using a focused ion beam to shave off the layers atom by atom, until they created the dome shape of the lens.

The team discovered that single layers of molybdenum disulphide, just 0.7nm thick, had remarkable optical properties: to a light beam, they acted as if they were 50 times thicker, at 38nm. This property, known as optical path length, determines the phase of the light and governs the interference and diffraction of light as it propagates.

"At the beginning we couldn't imagine why molybdenum disulphide had such surprising properties," said Lu. The explanation came from Zongfu Yu, an assistant professor at the University of Wisconsin, Madison, who developed a simulation that showed light was bouncing back and forth many times inside the high refractive index crystal layers before passing through.

This study, which is published in Light: Science and Applications, has revealed that a crystal of molybdenum disulphide has a refractive index, which is the property that quantifies the strength of a material's effect on light, of 5.5. For comparison, the refractive index of diamond is 2.4 and that of water is just 1.3.

This story is adapted from material from the Australian National University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.