Controlled-reflectance surfaces with film-coupled colloidal nanoantennas.
Controlled-reflectance surfaces with film-coupled colloidal nanoantennas.
复制标题
作者：
高效且可调的吸收对于各种应用至关重要，例如热光伏设备的受控发射率表面的设计；定制红外光谱以控制热耗散；和用于成像的探测器元件。基于金属元素的超材料作为吸收介质特别有效，因为超材料的电学和磁学特性都可以通过结构设计来调节。迄今为止，红外或可见光范围内的超材料吸收器是使用光刻图案化金属结构制造的，这使得它们本质上难以大面积生产，从而降低了它们的适用性。我们在这里展示了一种非常简单的方法，通过将化学合成的银纳米立方体随机吸附到金膜上的纳米级厚聚合物间隔层上来创建超材料吸收器，无需努力控制薄膜上立方体的空间排列，并表明薄膜耦合纳米立方体提供了可以通过改变几何形状来定制的反射光谱。每个纳米立方体都是著名的接地贴片天线的光学模拟，具有几乎相同的局部场结构，该结构通过金属介电函数的等离子体响应进行修改，并且具有异常大的吸收效率，这可以部分归因于干涉效应。使用这种方法可以控制大表面积的吸收率，其尺度超出了光刻方法（如电子束光刻）的范围，否则需要在纳米尺度上操纵物质。
Efficient and tunable absorption is essential for a variety of applications, such as the design of controlled emissivity surfaces for thermophotovoltaic devices; tailoring of the infrared spectrum for controlled thermal dissipation; and detector elements for imaging. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. To date, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures, making them inherently difficult to produce over large areas and hence reducing their applicability. We demonstrate here an extraordinarily simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale thick polymer spacer layer on a gold film –making no effort to control the spatial arrangement of the cubes on the film– and show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry. Each nanocube is the optical analog of the well-known grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches like e-beam lithography otherwise required to manipulate matter at the nanometer scale.