Two-dimensional tungsten disulfide monolayers synthesized from epitaxial oxides grown by Pulsed Laser Deposition

Description

The discovery of graphene has caught the attention of the scientific community and driven substantial research efforts for the investigation of other two-dimensional (2D) layered atomic crystals with a wide range of electronic and optical properties ranging from metallic to semiconducting structure Unlike graphene, 2D transition metal dichalcogenides (TMDs) possess tunable band gaps ranging from visible to near-infrared (between 1-2 eV). These appealing properties are crucial for building optoelectronic devices, such as single-layer transistors or photodetectors. Moreover, beyond structures consisting of atomically thin TMDs, heterostructures based on 2D TMDs with various bandgaps can serve as building blocks for future lightweight multi-junctional solar cells, light-emitting diodes, double heterojunction lasers, photodetectors, and other optoelectronic applications. Tungsten disulfide (WS2) is an intriguing representative of the semiconducting TMDs. Unlike its bulk counterpart, monolayer (1L) WS2 exhibits a direct bandgap of ~2 eV, as demonstrated by both theoretical and experimental studies. 1L-WS2 provides a convenient platform to design light emission from 2D confined excitonic systems due to the strong light absorption and emission at visible wavelengths that opens great opportunities for its integration in ultrathin optoelectronic devices. Here, we report on the reproducible and highly controllable two-step synthesis process of 1L-WS2 via high-temperature sulfurization in a sulfur-rich atmosphere of non-stoichiometric tungsten oxide films obtained by pulsed laser deposition (PLD) on atomically smooth sapphire. This approach yields 1L-WS2 with roughness and photoluminescence properties comparable to monolayers grown by chemical vapor deposition (CVD). Our results reveal that by changing the growth conditions in PLD, the stoichiometry of the epitaxial WOx films can be significantly varied. Moreover, we will show that the composition of the tungsten oxide films can have a significant impact on the quality of the 1L-WS2, and this was carefully examined by XPS, Raman spectroscopy, PL quantum yield measurement, SEM, AFM, and TEM analysis.

Period	31 May 2021 → 3 Jun 2021
Event title	2021 European Materials Research Society Spring Meeting
Event type	Conference
Location	FranceShow on map
Degree of Recognition	International