Guided Modes of Anisotropic van der Waals Materials Investigated by Near-Field Scanning Optical Microscopy

TL;DR

This study uses near-field scanning optical microscopy to investigate guided optical modes in anisotropic van der Waals materials, enabling direct measurement of their refractive indices in the visible spectrum.

Contribution

It introduces a method to directly measure anisotropic refractive indices of 2D van der Waals materials using near-field microscopy of guided modes.

Findings

Refractive indices of h-BN in the visible range were determined.

Dispersion relations of guided modes were characterized.

The method allows direct interaction studies between light and 2D materials.

Abstract

Guided modes in anisotropic two-dimensional van der Waals materials are experimentally investigated and their refractive indices in visible wavelengths are extracted. Our method involves near-field scanning optical microscopy of waveguide (transverse electric) and surface plasmon polariton (transverse magnetic) modes in h-BN/SiO2/Si and Ag/h-BN stacks, respectively. We determine the dispersion of these modes and use this relationship to extract anisotropic refractive indices of h-BN flakes. In the wavelength interval 550-700 nm, the in-plane and out-of-plane refractive indices are in the range 1.98-2.12 and 1.45-2.12, respectively. Our approach of using near-field scanning optical microscopy allows for direct study of interaction between light and two-dimensional van der Waals materials and heterostructures.