Topology-optimized (TO) dielectric photonic cavities enable light confinement below the diffraction limit.[1] Therefore, they are promising building blocks for integrating photonics and electronics. Scattering-type scanning near-field optical microscopy (s-SNOM) was used to characterize such cavities but suffers from a limited spatial resolution and the ability to measure the mode’s evolution in space.[1] Alternatively, electron energy loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM) has shown its potential for imaging optical excitations with high spatial resolution in three dimensions.[2-4]

In this study, we used a probe-corrected STEM equipped with a monochromator to acquire STEM-EELS maps of TO Si bow-tie cavities. The optimized cavity mode could be mapped due to the interaction of the electrons with the electric field supported by the cavity. Moreover, the acquired tilt series gave detailed information about the mode’s evolution in space. Advanced data processing allowed isolating the peaks corresponding to the mode of interest and the mapped relative intensities revealed the mode’s confinement around the bow-tie region.

The presented approach provides an avenue for comparing electric field simulations with the experimentally observed interaction of electrons with the electric field. Therefore, the presented preliminary results will help gain deeper insights into light confinement in TO dielectric photonic cavities.

References

[1] M. Albrechtsen Nat. Commun., 2022, 13, 6281.

[2] J.J. Cha Phys. Rev. B, 2010, 81, 113102.

[3] N. Le Thomas Phys. Rev. B, 2013, 87, 155314.

[4] D.T.L. Alexander ACS Nano, 2021, 15, 16501-16514.