Speaker
Description
Scattering-type scanning near-field optical microscopy (s-SNOM) and nanoscale infrared point spectroscopy (nano-FTIR) are powerful techniques for nanoscale optical mapping of various material properties. Both rely on elastic light scattering from an atomic force microscope tip illuminated by either monochromatic or broadband laser light. This metallic tip acts as an optical antenna, concentrating the illuminating field into a highly localized near field at its apex. By interferometrically recording the light scattered by the tip as it scans across the sample, s-SNOM generates near-field amplitude and phase images – revealing information about the local dielectric function when using monochromatic laser illumination. Alternatively, Fourier-transform spectroscopy of the tip-scattered field (using IR broadband illumination) enables nano-FTIR spectroscopy [1,2]. Beyond elastic scattering, the near-field microscope can detect inelastically scattered light, including techniques like tip-enhanced Raman spectroscopy and photoluminescence spectroscopy.
We utilize our s-SNOM setup to investigate the nanoscale optical properties of boron nitride (BN). In my talk I will focus on two different excitations in BN:
1. Phonon polaritons in BN layers: s-SNOM is widely used to generate and study phonon polaritons in hexagonal BN (hBN). While most works focus on exfoliated flakes, I will present new results on MOVPE grown hBN crystals. In contrast to previous studies, we observe clean polariton fringes only with a higher damping rate, i.e., a shorter propagation length, compared to their counterparts in exfoliated hBN. In addition, we demonstrate phonon polariton confinement in MOVPE grown isotopically pure BN micro-triangles and fully characterized the confined modes in these structures by s-SNOM and nano-FTIR measurements.
2. Color centers in hBN: These single-photon emitters (SPEs) represent an exciting system, as they provide stable and bright single-photon emission even at room temperature. We employ the near-field optical microscope, to detect PL signals in the visible spectral range influenced by the presence of the metallic tip (TAPL) and the near-field nanofocus (TEPL) [3].
References
[1] N. Ocelic, et al., Appl. Phys. Lett. 89, 101124 (2006).
[2] M. Schnell, et al., Nat. Commun. 5, 349 (2014).
[3] I. Niehues et al., Nanophotonics 14(3), 335-342 (2025).
