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Abstract NaCl has widely been used as a seeding promoter for chemical vapor deposition of large-scale 2D transition metal dichalcogenides. In this work, we report a study of the influence of NaCl on the growth and optical properties of layered CVD-grown WS2using steady-state and time-resolved Kerr rotation measurements at room temperature. Strong photoluminescence (PL) signals from single flakes grown with a low NaCl content indicates direct band-gap emission, whereas flakes grown with higher amounts of NaCl exhibit red-shifted, weaker PL. Raman measurements from single flakes also indicate that WS2grown with higher NaCl amounts result in multilayered structures, while lower NaCl quantities yield monolayer WS2. Ultrafast carrier decay measurements from single flakes also indicate a NaCl-dependent on the valley exchange interaction component (<10 ps) and slower decay components (>50 ps), attributed to a combination of phenomena, such as the band gap transitioning from direct to indirect and defect-related localized states. Our study provides insight into the influence of seeding promoters in layered CVD-grown WS2in particular and 2D transition metal dichalcogenides in general.
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Evolution of the Electronic Gap of Directly Synthesized Versus Mechanically Transferred WS 2 Monolayer to Multilayer Films
Abstract The electronic properties of 2D materials play a critical role in determining their potential for device applications. Despite rapid developments in 2D semiconductors, studies of fundamental electronic parameters, including the electronic gap and ionization energy, are limited, with significant discrepancies in reported values. The study focuses on tungsten disulfide (WS₂) and investigates the electronic structure of films comprising an increasing number of layers deposited with two different methods: direct synthesis via metal–organic chemical vapor deposition (MOCVD) and additive mechanical transfer of exfoliated single layers. The films are characterized via Raman, UV–vis, and photoluminescence spectroscopies, as well as ultraviolet photoelectron and inverse photoemission spectroscopies (UPS/IPES). The electronic gap of WS₂ is found to decrease from 2.43 eV for the monolayer to 1.97 eV for the trilayer, indicating a bulk transition at the trilayer thickness. This reduction in the electronic gap is primarily due to the downward shift of the conduction band minimum relative to the valence band maximum. A comparative analysis with MOCVD‐grown WS₂ reveals a slightly larger electronic gap for MOCVD‐grown samples, attributed to differences in defect densities. The electronic levels evaluated through UPS/IPES highlight the significant influence of preparation methods on the electronic properties of WS₂.
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- PAR ID:
- 10590956
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/admi.202401008
