Creating color and appearance of surfaces in real and Fourier space by tailored disorder

我们的实验-理论项目的目的是通过研究长程和短程无序以及分形和准晶排列来研究空间相关性对等离子体和介电纳米结构中无序的影响。我们希望确定两点相关函数、依赖于k的光学性质和依赖于波长的双向反射分布函数(BRDF)之间的关系，以便通过定制的无序来设计表面的颜色和外观。我们的想法是不仅允许创建代表CIE 1931颜色空间的不同颜色的不同光谱行为，而且允许表面的不同外观，即角度和偏振相关的光谱反射。特别是，我们将在规则和无序的一维和二维排列中使用金属和介电纳米颗粒。具体地说，我们将使用镁、金、铝、镍、银以及氧化铝、二氧化硅和氢氧化镁等介质来散射纳米天线。瑞利-伍德反常与等离子体色散交叉，可以增强或抑制特定偏振方向上的光谱散射和角散射。具有给定两点相关函数的定制空间无序函数，例如在纳米天线的大小、位置和取向上具有高斯或矩形无序分布的长程和短程无序，将提供定制光学响应的可能性。通过使用电子束光刻、胶体孔掩模或蚀刻光刻以及进一步的纳米结构技术来生成结构。在最新设计的同时傅里叶以及真实空间光谱和偏振分辨散射仪中测量它们的光学响应，可以获得必要的角度分辨BRDF数据。使用镁作为等离子体材料的一个特殊处理是它能够在氢化和随后的脱氢时执行从金属(镁)到介电(镁)的可逆相变。这使我们能够创建可以改变其颜色甚至外观的表面，类似于变色龙。在莫斯科与墨卡托研究员谢尔盖·蒂霍代夫教授的密切合作下，我们将开发和利用我们的理论来预测光谱、角度和偏振相关的BRDF数据。具体地，我们将使用耦合偶极子模型和共振态展开技术，我们将扩展到预测无序系统的角度相关的远场光谱。此外，我们首次旨在通过求解麦克斯韦方程结合复杂的介电材料函数从头开始预测各种无序表面的颜色外观。这将允许弥合向高级虚拟现实渲染软件的差距，到目前为止，该软件主要使用经验式和启发式模型来描述表面的外观。

The aim of our experiment-theory project is to study the influence of spatial correlations on disorder in plasmonic and dielectric nanostructures by investigating long- and short-range disorder as well as fractal and quasicrystalline arrangements. We want to determine the relationship between two-point correlation functions, k-dependent optical properties, and the wavelength-dependent bidirectional reflection distribution function (BRDF), in order to design the color and appearance of surfaces by tailored disorder.The idea is to not only allow for creating different spectral behavior that would represent the different colors from the CIE 1931 color space, but also allow for the different appearances of the surfaces, namely the angle- and polarization-dependent spectral reflectances.In particular, we are going to use metallic and dielectric nanoparticles in regular and disordered 1D and 2D arrangements. Specifically, we will utilize magnesium, gold, aluminium, nickel, silver, as well as dielectrics such as Al2O3, SiO2, and MgH2 for the scattering nanoantennas. Rayleigh-Wood anomalies crossing with plasmon dispersions can enhance or suppress spectral and angular scattering for certain polarizations in given directions. Tailored spatial disorder functions with given two-point correlation functions such as long- and short-range disorder with Gaussian or rectangular disorder distributions in size, position, and orientation of the nanoantennas will give the possibility to tailor the optical responses.Generating the structures is carried out by using electron-beam lithography, colloidal hole-mask or etching lithography, and further nanostructuring techniques. Measuring their optical responses in a newly designed simultaneous Fourier- as well as real-space spectral and polarization-resolved scatterometer gives the necessary angle-resolved BRDF data. A special treat of using magnesium as plasmonic material is its ability to perform reversible phase transitions from metallic (Mg) to dielectric (MgH2) upon hydrogenation and subsequent dehydrogenation. This allows us to create surfaces that can change their colors and even their appearances, similar to chameleons.In close collaboration with Mercator-Fellow Prof. Dr. Sergei Tikhodeev in Moscow, we will develop and utilize our theory for predicting the spectral, angular, and polarization-dependent BRDF data. In detail, we will be using a coupled-dipole model as well as the resonant state expansion technique, which we will extend towards predicting the angular-dependent far-field spectra of disordered systems.Additionally, for the first time, we aim at predicting ab initio the color appearance of various disordered surfaces by solving Maxwell’s equations in combination with complex dielectric material functions. This would allow for bridging the gap towards high-level virtual reality rendering software, where until now mostly empiric and heuristic models are used to describe the appearance of surfaces.