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Suppressed Percolation in Nearly Closed Gold Films

Stefano De Zuani ; Marcus Rommel (Institutionen för mikroteknologi och nanovetenskap, Nanotekniklaboratoriet) ; Bruno Gompf ; Audrey Berrier ; Jürgen Weis ; Martin Dressel
ACS Photonics (2330-4022). Vol. 3 (2016), 6, p. 1109-1115.
[Artikel, refereegranskad vetenskaplig]

Metal-dielectric composites exhibit remarkable properties at the percolation threshold. A small variation of the filling factor can lead to a huge variation in the dc conductivity from an insulator-like to a metal-like behavior while the real part of the permittivity diverges. This behavior can, in principle, be described by percolation theories at low frequencies and by effective medium approximations at higher frequencies. These theories assume a random distribution of the metallic inclusions inside the insulating matrix. But what happens in ordered structures when the percolation is deliberately suppressed? Even though a simple, nanometer-wide scratch can deteriorate the dc conductivity of a thin metal film, can it influence the mirror-like reflectivity? To address this question, we perform a systematic ellipsometric investigation on nearly closed Au films interrupted only by a two-dimensional periodic mesh of 20 nm wide lines. These nanostructured films have metal filling factors close to unity, but exhibit no dc conductivity. In the infrared, they show an antireflective behavior that can be tuned through the mesh periodicity. Surprisingly, the optical response of these structures can be modeled quite well by simple effective medium approximations. Increasing the size of the squares leads to a tunable, diverging, real part of the permittivity: A maximum of the real part of the permittivity of 1420 is found for the largest investigated squares in this study.

Nyckelord: antireflective properties; effective medium theory; percolation; spectroscopic ellipsometry



Denna post skapades 2016-07-11. Senast ändrad 2016-09-08.
CPL Pubid: 239231

 

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Institutioner (Chalmers)

Institutionen för mikroteknologi och nanovetenskap, Nanotekniklaboratoriet

Ämnesområden

Materialteknik

Chalmers infrastruktur