Electron Spectroscopy of Infrared Excitations at the Nanoscale

Plasmon-phonon coupled modes and surface phonon polaritons are key players in strong light-matter interaction and radiative heat transfer, respectively. Probing those excitations using spatially-resolved EELS has unveiled new exotic behavior extending our understanding of properties of infrared excitations at the nanoscale. We will discuss two EELS studies in nanosystems with compelling properties for nanophotonics and heat transfer applications: i) Spectroscopy and imaging of strongly-coupled plasmon-phonon modes in a double infrared antenna. Those hybrid modes are the result from a Rabi splitting as small as 26 meV, with coupling constant of 18 meV, fulfilling strong-coupling conditions. The spatial distribution of those plasmon-phonon modes was imaged providing insights into the local electromagnetic density of states. ii) Spectroscopy of surface phonon polaritons within nanoscale gaps. Gaps with distances ranging between 5 and 150 nm were fabricated to explore different regimes of phonon coupling as a function of temperature. Large variety of modes were probed within the gaps indicating multiple available channels for heat transfer processes. The spatial distribution of scattering across the nanogaps was determined revealing a strong temperature-dependent behavior, which suggest a complex interplay between thermal and vibrational behavior. Our work represents advances in the study of IR excitations sustained in nanostructures.