Exploiting Collective States in Superlattices

Abstract

Collective states with their fascinating optical properties occur through the coupling of dipole moments. The coupling of the dipoles leads to an overall optical response that varies strongly from the monomer. Dipole coupled systems are manifold systems with optical properties that are interesting for a variety of optoelectronic applications, solar cells, and catalytic reactions. The lattices range from atomic and molecular lattices up to plasmonic structures and can vary in their dimensionality. Depending on the approach, dipole coupled systems can easily be adapted to the relevant requirements, such as excitation energy. The first part of this work investigates collective states in one- and two-dimensional molecular lattices. These states are highly emissive, have narrow line widths as well as short radiative life times. With a microscopic real space dipole model, I show that excitations of two-dimensional molecular monolayers are robust against various forms of disorder. I realize the growth of two-dimensional monolayers with a perylene derivate and show that the collective states also exist on materials that provide a large radiative decay channel. Then I explore collective states in one-dimensional molecular aggregates, namely in molecule chains encapsulated in boron nitride nanotubes. I verify that the collective exitonic states of single- and multi-file chains show an enormous shift to lower energies that is not captured by the model of a chain of interacting dipoles. The last part of my work focuses on a different kind of dipole coupled system, namely bimetallic nanoparticle supercrystals for photocatalytic experiments. Small platinum particles that are placed in the hotspots of a gold supercrystal show an increased production of hydrogen. I investigate the layer dependent optical response of the crystal and calculate the electric fields in the hotspots which I compare with wavelength dependent catalytic experiments. In photocatalytic experiments the binary crystal shows a higher hydrogen generation rate than other top performers for formic acid dehydrogenation.