Opto-thermal interface engineering for room-temperature pyroelectric infrared sensing: from material characterization to experimental validation

Infrared sensing technologies are increasingly required in applications ranging from environmental monitoring and industrial diagnostics to autonomous systems, distributed sensing infrastructures, and ambient-condition monitoring. In this context, room-temperature pyroelectric sensors offer attractive features, including broadband response, low power consumption, simplified operation, and compatibility with scalable device architectures. Their response, however, does not depend only on the intrinsic properties of the pyroelectric material. A crucial role is played by the illuminated surface, where incident radiation is absorbed, converted into heat, and transferred to the active pyroelectric substrate. The opto-thermal interface is therefore a key element for controlling the transient thermal dynamics that generate the electrical signal. This thesis investigates opto-thermal interface engineering as a strategy to improve and understand room-temperature pyroelectric infrared sensing. Lithium niobate (LiNbO3) is used as a stable and reproducible pyroelectric platform, while solution-processable carbon-based materials are introduced as functional absorbing interfaces. Graphene oxide, graphite and graphite/poly(methyl methacrylate) (PMMA) coatings are considered as model systems because they allow the illuminated surface to be modified while preserving the same underlying pyroelectric substrate and avoiding complex microfabricated architectures. The aim is to establish a physically interpretable link between interface properties, photothermal conversion, transient temperature evolution, and device-level electrical response, with the pyroelectric material kept fixed as a reference transducer. A modelling and experimental framework is developed to describe the transduction chain from optical absorption to pyroelectric current generation. The model connects the effective absorbed power at the illuminated interface with the thermal response of the sensing stack and the resulting electrical output. This approach provides a basis for interpreting how surface absorptance, coating morphology, thermal coupling, and interfacial heat exchange influence the amplitude and temporal profile of the pyroelectric signal. In parallel, the thesis develops a methodological framework for characterizing complex carbon-based systems relevant to processable and surface-supported interfaces. Structural, optical, morphological, and opto-thermal analyses are combined with angular-resolved optical scattering to describe how carbonaceous coatings interact with incident radiation and redistribute light at the illuminated surface. A liquid-phase Brunauer–Emmett–Teller (BET) protocol based on methylene blue adsorption is also developed to estimate the accessible surface area of graphene-based systems and supported coatings. The resulting value provides an operational descriptor of surface accessibility under defined liquid-phase conditions, reflecting the measurement protocol and the material state instead of an intrinsic material constant. This is particularly relevant for soft, porous, assembled, and processable carbonaceous materials, whose accessible surface depends on dispersion state, aggregation, film morphology, and interaction with the probing environment. The interface descriptors obtained from these analyses, including optical absorptance, angular-resolved optical scattering, and liquid-phase accessible surface area, are used to support the interpretation of device measurements performed on LiNbO3-based pyroelectric sensors under controlled illumination conditions. Carbon-based coatings are deposited using scalable, low-temperature processes compatible with simple device fabrication. The comparison between Al-only, Al/graphene oxide, Al/graphite and Al/graphite/PMMA configurations shows that the illuminated interface strongly affects the measured transient current response. Graphite-based interfaces provide the strongest enhancement among the investigated systems, demonstrating the importance of broadband absorption, morphological complexity, and thermal boundary conditions in determining pyroelectric performance. PMMA encapsulation further modifies the response by introducing an additional optical and thermal interface, highlighting the trade-off between signal amplitude and relaxation dynamics. Overall, the results demonstrate that solution-processable carbonaceous coatings can act as effective opto-thermal interfaces for room-temperature pyroelectric infrared sensing. By modifying the illuminated surface while preserving the same pyroelectric substrate, it is possible to tune optical absorption, photothermal conversion, and transient response within a simple and scalable device architecture. The thesis thus develops two complementary and independently defensible contributions. The first is a reproducible experimental platform for room-temperature pyroelectric infrared sensing based on processable opto-thermal interfaces. The second is a methodological framework for characterizing soft, porous, and surface-supported carbon-based systems, combining liquid-phase BET and angular-resolved optical scattering. Together, these contributions establish interface engineering as a physically transparent route toward low-cost, room-temperature, broadband pyroelectric sensing.