Fabrication and characterization of plexcitonic hybrid systems for nanoscale heat-transfer measurements

Nowadays heat management at the nanoscale is a crucial technological issue, due to the ever growing diffusion of nanodevices at all levels. Heat diffusion at the nanoscale is fundamentally different with respect to the analogous macroscale phenomenon. The exchange of thermal energy at the macroscale is effectively describe by the Fourier’s law which is valid in the so-called “diffusive regime”, where the mean free path of heat carriers is much smaller than the size of the considered systems. At the nanoscale this condition can be misapplied causing the breakdown of the Fourier’s law. Depending on the composition, size and geometry of the considered systems many heat transport regimes can take place: from ballistic to hydrodynamic to heat confinement ones. Within this framework, there is a growing need for reliable nanothermometry experimental investigations; however, performing such measurements is a particularly challenging task. This is due to many factors, like the broadband and short-wavelength nature of heat-carrying phonons, the difficulty in fabricating nanostructures and the finite heat capacity of any solid-state thermal probe, which can affect the thermodynamics of the system under scrutiny, introducing unwanted artifacts. To perform nanothermometry measurements in a non-perturbative and reliable way, we propose nanothermometry devices where heating and sensing at the nanoscale are performed in the same system, employing light as a temperature readout method. Light has no thermal capacity making it a low-perturbative probe. The devices are characterized by three layers: heater layer, dielectric insulator and sensing layer. The heater layer has the role of converting an incident electromagnetic (EM) radiation into a localized increase of temperature, the dielectric layer separates the other two, avoiding any coupling between them and conducts heat from heaters to sensors, finally, the sensor layer is characterized by temperature-dependent optical properties enabling the temperature measurement through light. The thesis describes the fabrication and the characterization of two different nanothermometry devices, exploiting plasmonic nanostructures (NS) as heaters and bidimensional (2D) semiconductors as sensors. The experimental outcomes and the perspectives of the project conclude the thesis.