Disordered Network Metamaterials: Fundamentals and Applications

Abstract

Disordered plasmonics have attracted considerable attention for large-scale metamaterials, due to their robustness and broadband optical properties without the need for complex fabrication processes. These nanostructures are promising for a range of applications, including energy materials and photocatalysts. However, advancements in their design and experimental implementation have been limited by challenges in controlling their optical properties. This work explores the light-matter interaction in Disordered Network Metamaterials, provides a framework for understanding and engineering their optical properties, and introduces potential applications for these large-scale metamaterials. In the first part, a scalable design route and low-footprint strategy for the production of large-area, frequency-selective Cu–Sn disordered network metamaterials is presented. Furthermore, a framework that describes the optical response of these metamaterials using 2D Voronoi networks is introduced. This framework establishes a link between network topology and optical response. Moreover, it is demonstrated how the quasi-perfect absorption of these networks can be both designed and controlled through chemical engineering. Specifically, a linear relationship between the optical response and the Sn content is observed, spanning from the near-infrared to the UV region. As a result, the absorbing state exhibits strong sensitivity to changes in both the global network topology and the chemical composition. Through sequential self-assembly, the second part of this thesis goes beyond simple disordered networks by introducing a second phase in the form of Sn nanoparticles. Using electron energy loss spectroscopy, inhomogeneous localization of light in the network is demonstrated, concurrent with dipolar and higher-order localized surface plasmon modes of the nanoparticles. Coupling between the disordered networks and the nanoparticles is achieved without the use of a dielectric spacer. Furthermore, it is shown that the coupling strength deviates from the interaction of two classical dipoles when entering the strong coupling regime. Moving on to the third part, the possibility for coupling disordered network metamaterials to other resonant systems is expanded by the introduction of an ordered dielectric metasurface. Through a simple fabrication scheme, the elements of the dielectric metasurface are constructed with broken outof- plane symmetry. This new dimension in the design space maximizes the coupling between the two phases. To demonstrate the capabilities of the hybrid optical system, reconfigurable structural colors with extraordinary resolution are generated, achieving over 97%coupling efficiency and enabling local control of light matter interactions. Validated by experimental evidence, in the fourth part, an analytical model to calculate the local density of states of two-dimensional plasmonic graphs is presented. This approach provides insights into the properties of plasmonic networks and also serves as a model system for quantum graphs at optical frequencies. Specifically, the role of symmetry breaking is examined and it is demonstrated, how symmetry breaking can be leveraged as an effective tool for engineering the local density of states of plasmonic networks. The scalability, chemical adaptability, and high local density of states make disordered network metamaterials ideal for catalytic applications. In the final part of this thesis, the focus shifts beyond fundamentals to demonstrate the catalytic conversion of CO2 as a test-bed for real-world applications. By probing CuPd networks with electron energy loss spectroscopy it is shown that the enhancement of the local density of optical states coincides with Pd-rich regions in the chemically modulated network. While the systems still lacks total product selectivity, the catalytic production rate is on par with state-of-the-art catalysts for CO2 hydrogenation.