Janus Monolayer Transition Metal Dichalcogenides

TL;DR

This paper reports the synthesis, characterization, and analysis of a novel Janus monolayer transition metal dichalcogenide (SMoSe) with unique structural, electronic, and catalytic properties, including high hydrogen evolution reaction activity.

Contribution

It introduces a new Janus monolayer material with controlled S substitution on MoSe2 and provides comprehensive experimental and theoretical insights into its properties.

Findings

Successful synthesis of Janus SMoSe monolayer

Distinct Raman and photoluminescence signatures observed

High catalytic activity for hydrogen evolution reaction

Abstract

A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium atoms are substituted by sulfur atoms while the bottom selenium layer remains intact. The peculiar structure of this new material is systematically investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy and confirmed by transmission-electron microscopy and time-of-flight secondary ion mass spectrometry. Density-functional theory calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction (HER) activity is discovered for the Janus monolayer and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.