High‐Resolution Nanospectroscopy of Boron Nitride Nanotubes

Scattering type scanning near-field optical microscopy (s-SNOM) is an effective tool for the nanoscale examination of nano-objects. In this paper, we present a modified device setup that enables spectroscopic measurements with a tunable laser, even without an FTIR (Fourier Transform Infrared) spectroscopy add-on. We demonstrate the effectiveness of this setup by measurements on boron nitride nanotubes (BNNTs). In far-field absorption measurements, BNNTs have a characteristic peak around 1375 cm−1 due to a phonon polariton mode. This peak is also visible in near-field measurements along with several other peaks that are not present in the far-field spectrum. As these peaks are caused by local defects, their spatial distribution reveals the defect structure of individual nanotubes.