Paul H. Bittorf

Two-dimensional perovskites, such as Ruddlesden-Popper perovskites, exhibit outstanding optical properties and high exciton binding energies but are highly susceptible to degradation under photo- and electron-beam exposure. To overcome this limitation, we encapsulate the perovskites with mechanically exfoliated hexagonal boron nitride flakes, forming hexagonal boron nitride/perovskite heterostructures. Cathodoluminescence spectroscopy reveals that these heterostructures exhibit significantly reduced electron-beam-induced degradation, enhanced luminescence intensity, a narrower emission bandwidth, and an extended exciton decay time. Moreover, leveraging the scanning capability of our fiber-based cathodoluminescence spectroscopy technique, we demonstrate ultra-long-range exciton transport over distances of approximately 150 micrometers, attributed to exciton-defect coupling. This exciton-defect interaction not only enhances luminescence but also highlights the potential of hexagonal boron nitride/perovskite heterostructures as hybrid van-der-Waals systems with long-range exciton transport and slow radiative decay rates, paving the way for robust and efficient optoelectronic applications.

Strong electron-light interactions supported by the surface plasmon polaritons excited in metallic thin films can lead to faster optoelectronic devices. Merging surface polaritons with photonic crystals leads to the formation of Bloch plasmons, allowing for the molding of the flow of polaritons and the controlling of the optical density of states for even stronger electron-light interactions. Here, we use a two-dimensional square lattice of holes incorporated inside a plasmonic gold layer to investigate the interaction of surface plasmon polaritons with the square lattice and the formation of plasmonic Bloch modes. Cathodoluminescence spectroscopy and hyperspectral imaging are used for imaging the spatio-spectral near-field distribution of the optical Bloch modes in the visible to near infrared spectral ranges. In addition, the higher-order Brillouin zones of the plasmonic lattice are demonstrated by using angle-resolved cathodoluminescence mapping. We further complement our experimental results with numerical simulations of the optical modes supported by the plasmonic lattice that helps to better resolve the superposition of the various modes excited by the electron beam. Next to previous works in this context, our results thus place cathodoluminescence scanning spectroscopy and angle-resolved mapping as complementary techniques to uncover the spatio-spectral distribution of optical Bloch modes in real and reciprocal spaces.