# Effects of Hexagonal Boron Nitride Encapsulation on the Electronic Structure of Few-layer MoS$_2$

## TL;DR

This study combines theoretical and experimental Raman spectroscopy to show that hBN encapsulation affects the electronic structure of few-layer MoS$_2$, inducing strain and potentially altering its semiconducting properties.

## Contribution

It reveals that hBN encapsulation can induce strain in MoS$_2$, affecting its electronic properties, which challenges the assumption that hBN is electronically inert.

## Key findings

- hBN encapsulation causes shifts in Raman modes of MoS$_2$
- Encapsulation induces tensile strain in MoS$_2$ layers
- Strain may lead to K-Q crossover in conduction band

## Abstract

The hexagonal boron nitride (hBN) encapsulation has been widely used in the electronics applications of 2D materials to improve device performance by protecting 2D materials against contamination and degradation. It is often assumed that hBN layers as a dielectric would not affect the electronic structure of encapsulated 2D materials. Here we studied few-layer MoS$_2$ encapsulated in hBN flakes by using a combination of theoretical and experimental Raman spectroscopy. We found that after the encapsulation the out-of-plane A$_{1g}$ mode is upshifted, while the in-plane E$_{2g}^1$ mode is downshifted. The measured downshift of the E$_{2g}^1$ mode does not decrease with increasing the thickness of MoS$_2$, which can be attributed to tensile strains in bilayer and trilayer MoS$_2$ caused by the typical experimental process of the hBN encapsulation. We estimated the strain magnitude and found that the induced strain may cause the K-Q crossover in the conduction band of few-layer MoS$_2$, so greatly modifies its electronic properties as an n-type semiconductor. Our study suggests that the hBN encapsulation should be used with caution, as it may affect the electronic properties of encapsulated few-layer 2D materials.