Hybrid Plasmonics for Energy Harvesting and Sensing of Radiation and Heat

Abstract: The special optical properties of subwavelength metallic structures have opened up for numerous applications in different fields. The interaction of light with metal nanostructures leads to the excitation of collective oscillations of conduction-band electrons, known as plasmons. These plasmon excitations are responsible for the high absorption and high scattering of light in metallic nanostructures. High absorption of light and the subsequent temperature increase in the nanostructures make them suitable as point-like heat sources that can be controlled remotely by light.The research presented in this thesis focuses on the development and studies of hybrid devices that combine light-induced heating in plasmonic nanostructures with other materials and systems. Particular focus is put on hybrid organic-inorganic systems for applications in energy harvesting as well as in heat and radiation sensing. Harvesting energy from light fluctuations was achieved in a hybrid device consisting of plasmonic gold nanodisk arrays and a pyroelectric copolymer. In this concept, fast and efficient light-induced heating in the gold nanodisks modulated the temperature of the pyroelectric layer, which could be used to extract electrical energy from fluctuations in simulated sunlight.Integrating plasmonic nanostructures with complementary materials can also provide novel hybrid sensors, for monitoring of temperature, heat flux and radiation. In this thesis work, a hybrid sensor was designed based on the combination of a plasmonic gold nanohole layer with a pyroelectric copolymer and an ionic thermoelectric gel. The gold nanohole arrays acted both as broadband light absorbers in the visible to near-infrared spectral range of the solar spectrum and also as one of the electrodes of the sensor. In contrast to the constituent components when used separately, the hybrid sensor could provide both fast and stable signals upon heat or radiation stimuli, as well as enhanced equilibrium signals.Furthermore, a concept for heat and radiation mapping was developed that was highly sensitive and stable despite its simple structure. The concept consisted of a gel-like electrolyte connecting two separated metal nanohole electrodes on a substrate. Resembling traditional thermocouples, this concept could autonomously detect temperature changes but with several orders of magnitudes higher sensitivity. Owing to its promising sensing properties as well as its compatibility with inexpensive mass production methods on flexible substrates, such concept may be particularly interesting for electronic skin applications for health monitoring and for humanoid robotics. Finally, we improved the possibilities for the temperature mapping of the concept by modifying the structure from lateral to vertical form. Similar to the lateral device, the vertical temperature sensor showed high temperature sensitivity and stability in producing signals upon temperature changes.