Suppressed Percolation in Nearly Closed Gold Films
Suppressed Percolation in Nearly Closed Gold Films
复制标题
抑制近乎封闭的金膜中的渗透
DOI：
10.1021/acsphotonics.6b00198
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发表时间：
2016
期刊：
影响因子：
7
通讯作者：
Martin Dressel
中科院分区：
文献类型：
--
作者：
Stefano De Zuani;Marcus Rommel;Bruno Gompf;Audrey Berrier;Jürgen Weis;Martin Dressel
金属-介电复合材料在逾渗阈值处表现出显著的性能。填充因子的微小变化可以导致直流电导率从绝缘体状行为到金属状行为的巨大变化，同时介电常数的真实的部分发散。这种行为，在原则上，可以描述的渗流理论在低频率和有效介质近似在较高的频率。这些理论假设绝缘基体内的金属夹杂物的随机分布。但是，在有序结构中，当渗流被故意抑制时，会发生什么呢？即使一个简单的，纳米级的划痕可以降低薄金属膜的直流电导率，它会影响镜面反射率吗？为了解决这个问题，我们进行了系统的椭圆偏振调查近封闭的Au膜中断只有一个二维的周期性网格20 nm宽的线。这些纳米结构的薄膜具有接近于1的金属填充因子，但没有表现出直流导电性。在红外线中，它们显示出可以通过网格周期性进行调谐的抗反射行为。令人惊讶的是，这些结构的光学响应可以很好地模拟简单的有效介质近似。增加正方形的大小会导致介电常数的可调、发散、真实的部分：在本研究中，对于最大的调查正方形，发现介电常数的真实的部分的最大值为1420。
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.