Suppressed Percolation in Nearly Closed Gold Films

Abstract

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.

Interband transitions in semi-metals, semiconductors, and topological insulators: a new driving force for plasmonics and nanophotonics [Invited]

“…In the first case, an interband plasmonic origin was claimed for the resonances. In the second case, it was proposed that the oxynitride consists of a mixture of two phases that mimics at the macroscopic scale the visible optical response of an interband plasmonic material, in an analogous way to an earlier report from De Zuani et al [108] that showed huge effective 1 values (up to 1000!) in nearly closed Au films.…”

White Light Generation and Anisotropic Damage in Gold Films near Percolation Threshold

“…As the average film thickness increases during the metal deposition, individual and well-separated metal islands extend their sizes, eventually forming near the percolation threshold a semicontinuous film that gradually evolves into a homogeneous smooth film exhibiting (close to) bulk properties . The percolation threshold can experimentally be observed by monitoring FE effects with optical methods − , and uniquely determined in the low-frequency regime through electric conductivity measurements. , It should also be noted that the average film thickness corresponding to the percolation threshold depends strongly on the deposition conditions, substrate material, and metal involved. , …”

Chemical tuning of molecular quantum materials κ-[(BEDT-TTF)1−x(BEDT-STF)x]2Cu2(CN)3: from the Mott-insulating quantum spin liquid to metallic Fermi liquid

“…64 In general, the divergency of the dielectric permittivity e 1 (x) is a hallmark of percolative phase transitions in microemulsions, [65][66][67][68][69] composites [70][71][72] or and percolating metal films. [73][74][75][76][77] Since audio-and radio-frequency experiments are more suitable for exploring the dielectric behavior at the insulatormetal transition, we have conducted dielectric experiments down to 7.5 kHz. Fig.…”