Infrared-Enhanced Electron Emission from Nanoantennas for Optical Detection

Within optical systems, Infrared (IR) detectors are a key focus of research because of the need for low-power, high-performance, versatile devices. In this context, many works presented plasmonic nanostructures as candidates for next-generation detectors. Conventional IR technologies are limited by a trade-off between system requirements and performance. Microbolometers exploit thermal phenomena; they operate at room temperature but suffer from slow response and low sensitivity. Meanwhile, semiconductor detectors offer superior performance but require cryogenic cooling, since their working principle relies on the photoelectric effect. This work explores an alternative approach based on plasmonic nanoantennas engineered for Schottky-mediated electron emission. Electromagnetic and thermal simulations led to the design of new geometries, whose properties have been optimized for resonance conditions, field enhancement, and thermal hotspot formation. Initial steps relied on the analysis of previous reports addressing photocurrent in similar structure as a result of Fowler–Nordheim tunneling. Further analysis, however, pointed instead to a different interpretation given by the combination of three regimes: Schottky emission at low bias, Fowler–Nordheim tunneling at higher bias, and space-charge saturation. This thesis aims to demonstrate that Schottky emission can be engineered to produce room-temperature IR detector devices. Fabrication process employed electron-beam lithography, thin-film deposition, and substrate underetching, while scanning electron microscopy (SEM) and elemental analysis verified nanogap integrity and revealed process challenges such as gold damage and residual oxides. A custom optical setup integrating an FTIR source, off-axis parabolic mirrors, and lock-in detection has been designed and realized to conduct photocurrent measurements under IR illumination. Initial tests confirmed measurable photoresponse consistent with Schottky emission, validating the proposed mechanism. These results indicate the feasibility of plasmonic nanoantenna-based IR detection at room temperature and provide a basis for further optimization and for the development of more complete imaging systems.