22 Aug 2008
Nanostructured gold films can be used as effective broadband terahertz antireflection coatings, say scientists in Germany.
The researchers used the concept of "impedance matching": previous work has shown that ultrathin metallic coatings suppress reflections of electromagnetic radiation over a much broader bandwidth than conventional dielectric antireflection coatings. However, the bandwidth of the coating was limited by the frequency-dependent properties of the bulk metal films employed in these earlier experiments (Phys. Rev. B 77 195405).
Now, the Freiburg researchers have overcome this problem by using a discontinued gold film that has a different conductivity than bulk gold thanks to its nanostructure. "It turns out that the characteristic behaviour of the nanostructured film allows us to achieve nearly perfect impedance matching over a very broad frequency range," Thoman told nanotechweb.org.
The scientists also showed that, in principle, other coating techniques, such as cluster deposition, can be employed to create nanostructured films that work as antireflection coatings.
The researchers now plan to investigate how the terahertz antireflection properties of their nanostructured films vary with temperature. "This might help us fine-tune the performance of the coating," said Thoman. "Of course, we then want to coat active terahertz devices and test their performance."