Optical investigation of the natural electron doping in thin MoS2 films deposited on dielectric substrates

TL;DR

This study investigates how the dielectric environment affects the optical and electronic properties of monolayer MoS2 films, revealing that surface interactions and charging significantly influence their photoluminescence behavior.

Contribution

It demonstrates that encapsulating MoS2 with dielectrics like SiO2 and SiN reduces surface-induced charge variations, leading to more uniform optical properties and advancing understanding of surface effects in 2D materials.

Findings

PL spectra vary widely on SiO2 substrates

Encapsulation improves mechanical coupling and uniformity

Negative charging increases with encapsulation

Abstract

Two-dimensional (2D) compounds provide unique building blocks for novel layered devices and hybrid photonic structures. However, large surface-to-volume ratio in thin films enhances the significance of surface interactions and charging effects requiring new understanding. Here we use micro-photoluminescence (PL) and ultrasonic force microscopy to explore the influence of the dielectric environment on optical properties of a few monolayer MoS2 films. PL spectra for MoS2 films deposited on SiO2 substrates are found to vary widely. This film-to-film variation is suppressed by additional capping of MoS2 with SiO2 and SiN, improving mechanical coupling of MoS2 with surrounding dielectrics. We show that the observed PL non-uniformities are related to strong variation in the local electron charging of MoS2 films. In completely encapsulated films, negative charging is enhanced leading to uniform optical properties. Observed great sensitivity of optical characteristics of 2D films to surface interactions has important implications for optoelectronics applications of layered materials.