Spectroscopic Observation and Modeling of Photonic Modes in CeO₂ Nanostructures

Photonic modes in dielectric nanostructures, e.g., wide gap semiconductor like CeO₂ (ceria), have the potential for various applications such as information transmission and sensing technology. To fully understand the properties of such phenomenon at the nanoscale, electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope was employed to detect and explore photonic modes in well-defined ceria nanocubes. To facilitate the interpretation of the observations, EELS simulations were performed with finite-element methods. The simulations allow the electric and magnetic field distributions associated with different modes to be determined. A simple analytical eigenfunction model was also used to estimate the energy of the photonic modes. In addition, by comparing various spectra taken at different location relative to the cube, the effect of the surrounding environment on the modes could be sensed. This work gives a high-resolution description of the photonic modes’ properties in nanostructures, while demonstrating the advantage of EELS in characterizing optical phenomena locally.