Strong Photoluminescence Enhancement of MoS2 through Defect Engineering and Oxygen Bonding

TL;DR

This study demonstrates that defect engineering and oxygen bonding significantly enhance the photoluminescence of monolayer MoS2, offering a new approach to modulate optical properties for optoelectronic applications.

Contribution

The paper introduces a novel method of defect engineering combined with oxygen bonding to achieve large PL enhancement in MoS2, supported by experimental and theoretical analysis.

Findings

PL enhancement up to thousands of times at defect sites

Oxygen adsorption induces heavy p doping and exciton conversion

Defect engineering via oxygen plasma is effective and stable

Abstract

We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro- PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high temperature vacuum annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of non-radiative recombination of excitons at defect sites as verified by low temperature PL measurements. First principle calculations reveal a strong binding energy of ~2.395 eV for oxygen molecule adsorbed on an S vacancy of MoS2. The chemical adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physical adsorbed oxygen on ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices.