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Ordered and Disordered Phases in Mo1-xWxS2 Monolayer
Wei Tan1, Zhipeng Wei2, Xiaomin Liu1
1State Key Laboratory of High Power Semiconductor Laser, Changchun University of Science and Technology, Changchun, 130022, China.
Scientific Reports
|November 11, 2017
Summary
This study investigates monolayer molybdenum-tungsten disulfide (Mo1-xWxS2) alloys. Ordered phases exhibit smaller band gaps and distinct electronic properties compared to disordered phases, with phase transitions occurring around 41-43 K.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Materials Science
Background:
- Monolayer transition metal dichalcogenides (TMDs) like MoS2 and WS2 are promising for electronic and optoelectronic applications.
- Alloying MoS2 with WS2 (Mo1-xWxS2) allows tuning of their properties.
- Understanding the structural and electronic differences between ordered and disordered alloy phases is crucial for material design.
Purpose of the Study:
- To explore the structural and electronic properties of monolayer Mo1-xWxS2 alloys in both ordered and disordered phases.
- To investigate the influence of composition (x) and degree of order on phase transitions and electronic band structures.
- To analyze the impact of phase order on band edge positions, band mixing, band splitting, band gap, and effective masses.
Main Methods:
- Utilized a combination of the special quasirandom structure (SQS) approach and the cluster expansion (CE) method.
- Employed first-principle calculations to determine structural and electronic properties.
- Analyzed phase transitions, band edge alignments (VBM and CBM), band mixing, and effective masses.
Main Results:
- Identified phase transitions from ordered to disordered states at 41 K (x=1/3) and 43 K (x=2/3).
- Found that the valence band maximum (VBM) edge depends on composition (x), while the conduction band minimum (CBM) edge is sensitive to W concentration and the degree of order.
- Observed distinct band mixing near the CBM in disordered phases (Mo- and W-character bands mixed) versus ordered phases (bands separated), leading to smaller band gaps in ordered phases.
Conclusions:
- The degree of structural order significantly impacts the electronic properties of Mo1-xWxS2 alloys, particularly near the conduction band minimum.
- Ordered phases exhibit larger band splitting and smaller band gaps compared to disordered phases.
- Electron and hole effective masses differ between ordered and disordered phases, with implications for charge transport in these materials.
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