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Abstract Engineering electronic bandgaps is crucial for applications in information technology, sensing, and renewable energy. Transition metal dichalcogenides (TMDCs) offer a versatile platform for bandgap modulation through alloying, doping, and heterostructure formation. Here, the synthesis of a 2D MoxW1‐xS2graded alloy is reported, featuring a Mo‐rich center that transitions to W‐rich edges, achieving a tunable bandgap of 1.85 to 1.95 eV when moving from the center to the edge of the flake. Aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy showed the presence of sulfur monovacancy, VS, whose concentration varied across the graded MoxW1‐xS2layer as a function of Mo content with the highest value in the Mo‐rich center region. Optical spectroscopy measurements supported by ab initio calculations reveal a doublet electronic state of VS, which is split due to the spin‐orbit interaction, with energy levels close to the conduction band or deep in the bandgap depending on whether the vacancy is surrounded by W atoms or Mo atoms. This unique electronic configuration of VSin the alloy gave rise to four spin‐allowed optical transitions between the VSlevels and the valence bands. The study demonstrates the potential of defect and optical engineering in 2D monolayers for advanced device applications.
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Spatially Composition-graded Monolayer WSe2xTe2−2x Nanosheets
Alloying in two-dimensional (2D) transition metal dichalcogenides (TMD) has allowed bandgap engineering and phase transformation, which provide more flexibility and functionality for electronic and photonic devices. To date, many ternary TMD alloys with homogenous compositions have been synthesized. However, realization of bandgap modulation spatially within a single TMD nanosheet remains largely unexplored. In this work, we demonstrate the synthesis of spatially composition-graded WSe2xTe2-2x flakes using an in situ chemical vapor deposition method. The photoluminescence and Raman spectra line-scanning characterization indicate a spatially graded bandgap, which increases from 1.46 eV (center) to 1.61 eV (edge) within one monolayer flake. Furthermore, the electronic devices based on this spatially graded material exhibit tunable transfer characteristics.
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- Award ID(s):
- 1653241
- PAR ID:
- 10328633
- Date Published:
- Journal Name:
- 52th IEEE Semiconductor Interface Specialists Conference
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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