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

**Source**: https://www.cs.tum.de/spp1839/projects/2nd-period-2018-2021/06.html
**Parent**: https://www.cs.tum.de/spp1839/projects.html

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, aluminum,
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 the tailored 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.

## Contributors

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Prof. Harald Giessen

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Florian Sterl

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Prof. Thomas Weiss

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Swaathi Upendar

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