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Updated: May 18, 2026

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope
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Unusual Defect-Related Room-Temperature Emission from WS2 Monolayers Synthesized through a Potassium-Based Precursor
Peter Walke1, Reelika Kaupmees1, Maarja Grossberg-Kuusk1
1Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
Abstract:
Alkali-metal-based synthesis of transition metal dichalcogenide (TMD) monolayers is an established strategy for both ultralarge lateral growth and promoting the metastable 1T phase. However, whether this can also lead to modified optical properties is underexplored, with reported photoluminescence (PL) spectra from semiconducting systems showing little difference from more traditional syntheses. Here, we show that the growth of WS2 monolayers from a potassium-salt precursor can lead to a pronounced low-energy emission in the PL spectrum. This is seen 200-300 meV below the A exciton and can dominate the signal at room temperature. The emission is spatially heterogeneous, and its presence is attributed to defects in the layer due to sublinear intensity power dependence, a noticeable aging effect, and insensitivity to washing in water and acetone. Interestingly, statistical analysis links the band to an increase in the width of the A1g Raman band. The emission can be controlled by altering when hydrogen is introduced into the growth process. This work demonstrates intrinsic and intense defect-related emission at room temperature and establishes further opportunities for tuning TMD properties through alkali-metal precursors.
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