Periodic Reporting for period 3 - VISIRday (VISible to far-IR optical tuning: passive DAYtime cooling by hierarchical structures and hybrid materials)
Reporting period: 2020-03-01 to 2021-08-31
This is a difficult task to achieve and will only be possible by addressing fundamental materials science research across multiple length scales.
The overall goal to master this challenge is to combine top-down direct write lithography with controlled bottom-up colloidal self-assembly. This allows creating hierarchically structured systems fully addressing the stringent optical properties, which cover the entire spectral range from 300 nm – 20 µm. The colloidal nano- and mesoparticles of interest will consist of novel surface phonon polariton (SPhP) supporting materials, which feature tuneable sky window absorption properties depending on their size, shape, and composition. Conjugation of hierarchical structures with such mid-infrared designed SPhP particles enables to meet the specific demands for broadband optical tuning.
We also plan to combine these novel nanophotonic materials with polymers and metallic nanostructures. Such hybrid devices could feature finely adjusted and even externally tunable optical properties, allowing for switching of the cooling capacity.
Based on this fundamental work, VISIRday strives to provide concepts for functional paints and fibers - advanced materials that enable passive daytime cooling as a new green energy technology.
Which synthesis route is most suitable to access well-defined materials with adjustable surface phonon polariton properties? For this, we investigate (inert) calcination routes to convert silica particles into silicon carbide objects in combination with colloidal self-assembly. Up to now, we succeeded in a low-temperature conversion strategy to yield SiC nanostructures. We were also successful in the fabrication of non-spherical colloidal particles, which are now being scaled up. We also strive to tune their surface phonon polariton properties.
Which microstructure is most effective in transmitting, absorbing, and emitting in the mid-infrared range? For this, we develop photolithographic strategies to generate microstructures in a wide variety of materials. We succeeded in the development of suitable photoresist and development strategies and are now optimizing the lift-off process to gain free-standing structures.