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UNAM team harvests light on springs

Despite their versatility in many other aspects, nanomaterials are surprisingly limited when it comes to the absorption of light: Many of these featherweight structures simply aren’t thick enough to bring photons to a halt. Nevertheless, light harvesting is vital for precisely the sort of devices that would benefit the most from nanotechnology, and Dr. Tural Khudiyev and Dr. Mehmet Bayındır, two researchers at Bilkent University’s National Nanotechnology Research Center (UNAM), have recently developed a type of nanomaterial that stands above the rest in the capture of light across the visible range in particular.

Published in the journal Applied Optics, the group’s design involves conventional nanowires that are twisted into springs through minor alterations in temperature during the fiber-drawing process used in their production. This configuration allows light-absorbing “hotspots” to form across the length of the spring, which trap incident light through the Mie effect and increase the material’s absorption efficiency by 23% compared to non-modified nanowire structures. As with many other nanomaterials, structure diameter appears to be key for this effect: The group’s theoretical calculations suggest that optimal absorption occurs for spring diameters between 50 and 200 nanometers, the material’s effectiveness tapering out beyond this range and even falling behind that of nanowires for diameters over 400 nm. In addition to single nanowires, theoretical predictions suggest that large arrays of nanosprings may also exhibit enhanced absorption, provided that the spacing length between individual springs is optimized beforehand.

The group also predicts that core-shell nanosprings may reach even higher absorption efficiencies, and suggests that such a scheme would be of considerable use in photovoltaic and photodetector devices that must absorb a high number of photons using as little material as possible. Their research was highlighted by the Reuters and also received international attention from the materials science community by being highlighted in Nanowerk, phys.org, Photon Transfer, Top Wire and other news aggregates.

Nanosprings harvest light more efficiently