# 07 - Scattering Interfaces with Tailored Disorder

**Source**: https://www.cs.tum.de/spp1839/projects/1st-period-2015-2018/07.html
**Parent**: https://www.cs.tum.de/spp1839/projects.html

Light scattering interfaces play an importance
role in many applications of optics and photonics. For example, in
photovoltaics they enhance light trapping and thus the efficiency of
solar cells. In particular, stochastic interfaces have proven
advantageous due to their spectrally broadband and efficient
performance. Nevertheless, light scattering abilities of
state-of-the-art interfaces remain limited. Particularly, tailoring the
surface topography and with that the ability to scatter light is
severely restricted by the fabrication methods considered thus far. Due
to a lack of suitable techniques, it can be safely assumed that the
full potential of disordered scattering interfaces has not been fully
explored yet. In this project we desire to explore a promising approach
to solve this issue. We aim to fabricate and investigate disordered
interfaces with well-controlled topographies. Control over topography
enables us to control the interaction of light with these systems as
well. Our approach facilitates the fabrication of sample systems with
scattering properties on demand. This concerns far-field properties,
such as a predefined angular distribution of the scattered light for a
specific spectral range, as well as near-field properties, such as
luminescence enhancement of quantum emitters located in the vicinity of
the interface. The key of our approach is to use a polydisperse
colloidal solution as the starting point to fabricate the interface.
The solution contains spheres with sizes ranging from several tens of
nm to a few µm. It is deposited onto a substrate on which the spheres
will form a dense monolayer. The exact position of each sphere and
their arrangement is random.

However, the size distribution of the colloidal
solution determines the topographical parameters of the surface, e.g.
correlation length and average height. The deposited monolayer provides
the referential topography that is subsequently transformed into an
interface, e.g. using adapted thin-film deposition techniques. This
final interface shall feature the desired scattering properties. The
size distribution of the colloidal solutions here is the central lever:
By carefully tailoring the size distribution, the topography of the
interfaces is managed easily and fast. Identifying suitable size
distributions to control the scattering properties upon request is one
major challenge of our project. Exemplary application cases for our
interfaces chosen here are simplified sample systems. On the one hand,
we want to increase the light absorption in thin Si films. On the other
hand, we aim at enhancing the luminescence of integrated quantum
emitters. But our approach is not limited to these applications. Further
application areas not addressed here are, e.g., random lasing or
imaging of objects behind diffusive media. Beyond that, our proposed
system constitutes an ideal platform to investigate fundamental physical
phenomena, such as Anderson localization.

## Contributors

- [Prof. Carsten Rockstuhl](https://www.tfp.kit.edu/rockstuhl.php "Opens internal link in current window")
- Aimi Abass
- Stefan Nanz
- [Prof. Ralf B. Wehrspohn](https://www.imws.fraunhofer.de/de/institut/organisation/institutsleitung.html "Opens internal link in current window")
- Alexander Sprafke
- Peter Piechulla

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