Excited states in hydrogenated single-layer MoS₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Chemistry

Background:

• Single-layer molybdenum disulfide (MoS2) is a promising 2D material with tunable electronic and optical properties.
• Understanding the effects of chemical functionalization on MoS2 is crucial for its technological applications.
• Previous studies have explored doping and defect engineering in MoS2, but the impact of hydrogenation requires further investigation.

Purpose of the Study:

• To investigate the electronic and optical properties of single-layer MoS2 upon hydrogenation using theoretical calculations.
• To explore the formation and characteristics of excitonic states in hydrogenated MoS2.
• To compare the effects of hydrogenation with alkali metal (Li, Na) doping on MoS2.

Main Methods:

• Density-matrix based time-dependent density-functional theory (TDDFT) calculations were employed.
• The excitation spectrum and absorption spectrum of MoS2 at various hydrogen coverages were computed.
• Spin polarization and the nature of mid-gap states were analyzed.

Main Results:

• Fully hydrogenated MoS2 exhibits metallic behavior.
• Lower hydrogen coverages lead to spin-polarized, localized mid-gap states, resulting in novel excitonic peaks.
• Hydrogenation significantly suppresses visible light photoluminescence, consistent with experimental findings, while Li/Na doping creates n-doped semiconductors without excitonic states.

Conclusions:

• Hydrogenation is an effective strategy for tuning the optical properties of single-layer MoS2, with potential for creating new optoelectronic devices.
• The observed large binding energies of excitons in hydrogenated MoS2 facilitate experimental detection.
• Hydrogenation offers a distinct pathway for modifying MoS2 properties compared to alkali metal doping.