Three-dimensional Near-field Analysis Through Peak Force Scattering-type Near-field Optical Microscopy

TL;DR

This paper introduces a three-dimensional near-field analysis method using peak force scattering-type near-field optical microscopy to map and tune polaritonic modes in 2D materials with high spatial resolution.

Contribution

It demonstrates 3D near-field characterization of polaritons in hexagonal boron nitride using PF-SNOM, revealing momentum quantization and tunability along the perpendicular axis.

Findings

Revealed momentum quantization of polaritons in micro-disk structures.

Showed tip-sample distance can tune polariton momentum.

Provided detailed 3D near-field maps of nano-photonics structures.

Abstract

Scattering-type scanning near-field optical microscopy (s-SNOM) is instrumental in exploring polaritonic behaviors of two-dimensional (2D) materials at the nanoscale. A sharp s-SNOM tip couples momenta into 2D materials through phase matching to excite phonon polaritons, which manifest as nanoscale interference fringes in raster images. However, s-SNOM lacks the ability to detect the progression of near-field property along the perpendicular axis to the surface. Here, we perform near-field analysis of a micro-disk and a reflective edge made of isotopically pure hexagonal boron nitride (h-11BN), by using three-dimensional near-field response cubes obtained by peak force scattering-type near-field optical microscopy (PF-SNOM). Momentum quantization of polaritons from the confinement of the circular structure is revealed in situ. Moreover, tip-sample distance is found to be capable of fine-tuning the momentum of polaritons and modifying the superposition of quantized polaritonic modes. The PF-SNOM-based three-dimensional near-field analysis provides detailed characterization capability with a high spatial resolution to fully map three-dimensional near-fields of nano-photonics and polaritonic structures.