§Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, United States.
ACS Nano. 2015 Mar 24;9(3):3284-92. doi: 10.1021/acsnano.5b00412. Epub 2015 Mar 10.
There has been strong, ongoing interest over the past decade in developing strategies to design and engineer materials with tailored optical properties. Fractal-like nanoparticles and films have long been known to possess a remarkably broad-band optical response and are potential nanoscale components for realizing spectrum-spanning optical effects. Here we examine the role of self-similarity in a fractal geometry for the design of plasmon line shapes. By computing and fabricating simple Cayley tree nanostructures of increasing fractal order N, we are able to identify the principle behind how the multimodal plasmon spectrum of this system develops as the fractal order is increased. With increasing N, the fractal structure acquires an increasing number of modes with certain degeneracies: these modes correspond to plasmon oscillations on the different length scales inside a fractal. As a result, fractals with large N exhibit broad, multipeaked spectra from plasmons with large degeneracy numbers. The Cayley tree serves as an example of a more general, fractal-based route for the design of structures and media with highly complex optical line shapes.
在过去的十年中，人们一直强烈关注开发具有定制光学性能的材料的设计和工程策略。分形样纳米粒子和薄膜长期以来一直被认为具有非常宽的光响应带宽，并且是实现光谱扩展光学效果的潜在纳米级组件。在这里，我们研究了自相似性在分形几何中的作用，以设计等离子体线形状。通过计算和制造具有增加分形阶数 N 的简单凯莱树纳米结构，我们能够确定该系统的多模等离子体光谱如何随着分形阶数的增加而发展的原理。随着 N 的增加，分形结构获得了越来越多的具有某些简并度的模式：这些模式对应于分形内部不同尺度上的等离子体振荡。因此，N 较大的分形表现出具有大简并数的等离子体的宽、多峰光谱。凯莱树是用于设计具有高度复杂光线路形状的结构和介质的更通用的基于分形的途径的一个例子。
