# Facile Projection of Spatially Resolved Refractive Index Modulation in Monolayer MoS2 via Light Phase Changes

## TL;DR

This paper introduces a new non-destructive method to map refractive index changes in MoS2 using hyperspectral phase microscopy, enabling precise visualization of strain-induced effects.

## Contribution

A novel hyperspectral phase microscopy technique is developed to directly visualize refractive index modulation in MoS2 without complex theoretical calculations.

## Key findings

- Hyperspectral phase microscopy efficiently maps refractive index changes in MoS2 induced by strain.
- Phase difference (Δϕ) is selectively sensitive to refractive index (n) modulation under specific wavelengths and substrate thickness.
- A linear relation between n and Δϕ allows precise visualization of excitonic band modulation with R² > 0.97.

## Abstract

Fast spatial contouring of the complex refractive index (n  +  ik) of semiconducting materials is a much sought‐after goal since the advent of semiconductor‐related industries. This study develops a novel metrology to shape the refractive index modulation of materials using hyperspectral phase microscopy by maximizing the light‐matter interaction of physical properties. The facile, non‐destructive, and wide‐field hyperspectral phase technique realizes efficient visualization of the spatially resolved refractive index nature induced by strain within and among examined MoS2 materials. Furthermore, numerical analyses based on a steady‐state transfer matrix clarify that the spectral phase difference (Δϕ) is selectively sensitive to the modulation of refractive index (n) but not of extinction coefficient (k) under certain wavelength ranges. This dependence is associated with wavelength and the thickness of the dielectric layer on the substrates. Simple linear relation between n and Δϕ for ≈100 nm of SiO2, dielectric material supporting MoS2, enables to visualize the excitonic A and B band modulation, and furthermore, refractive index with fairly high precision (coefficient of determination, R
2 > 0.97 in the wavelength range of 530–630 nm).

The modulation of refractive index (n) is visualized by using hyperspectral phase microscopy, where light‐matter interaction is maximized through substrate engineering. In specific wavelengths and oxide thickness of the substrate, the phase difference can directly reflect the refractive index. Furthermore, a spatially resolved refractive index distribution map of MoS2 is acquired without theoretical calculations. MoS2 samples in which strain is induced are examined by hyperspectral phase microscopy and conventional spectroscopy.