Antennas for more Efficiency
Nanoantennas of the Highest Precision
In the future, tiny antennas made of metal with the ability to capture sunlight might lead to more efficient photovoltaic power generation. Physicists of the University of Würzburg have now produced such antennas from gold – with a previously unheard of precision. Nanoantennas can collect light and concentrate it into tiny spaces – similarly to a burning lens, but much more efficiently. This allows a more efficient utilization of light energy.
Initial examinations of the antennas show the great potential of the new method - Picture: Uni Würzburg
There are many applications for these optical antennas, ranging from photovoltaics to integrated circuits that work with light instead of electrons. However, the production of optical nanoantennas is quite tricky. “They need to be about 300 nm in length and include a gap of less than 10 nm – in which the light is collected,” explains Professor Bert Hecht of the Physics Department at the University of Würzburg. These are extremely small dimensions. Unless fabricated on this scale, the antennas are not able to concentrate the light properly.
Why are they made of gold? “This is because gold is chemically stable in air,” says Bert Hecht. You could also use silver, since it allows the production of optical antennas with even better characteristics. But silver is not stable in air. In collaboration with researchers from Dübendorf (Switzerland) and Milan (Italy), Professor Hecht’s Würzburg team has found a way to produce such antennas by a method showing great potential. Chemical self-organization afforded gold flakes which consisted of a single gold crystal and hence were free from any internal granular structure. The researchers used ion beam milling to fabricate nanostructures from these flakes, which are impressive in their precision: The cut edges are flat like a single layer of gold atoms.
Optical antennas produced in this way concentrate the light in their gaps ten times better than conventional antennas. This new method now enables the researchers to create complex large-area structures reliably without any imperfections. In the coming years, the Würzburg physicists are going to explore the potential of nanoantennas in a project funded by the Volkswagen Foundation (Hannover) as part of a program entitled “Integration of Molecular Components in Functional Macroscopic Systems”. Additional funds are provided by the German Research Foundation (DFG) within priority program 1391 “Ultrafast Nano-Optics”.
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