2023 Fiscal Year Annual Research Report
Symmetry-directed Epitaxy Growth of 2D Semiconducting Transition Metal Dichalcogenides with continuous single crystallinity and ultralow defect density
| Project/Area Number |
23H00253
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| Research Institution | The University of Tokyo |
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Principal Investigator |
トン ヴィンセント 東京大学, 大学院工学系研究科(工学部), 教授 (50971628)
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| Co-Investigator(Kenkyū-buntansha) |
長汐 晃輔 東京大学, 大学院工学系研究科(工学部), 教授 (20373441)
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| Project Period (FY) |
2023-04-01 – 2026-03-31
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| Keywords | Symmetry / mono-orientation / sapphire / MoS2 / epitaxy growth |
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| Outline of Annual Research Achievements |
In commercially available sapphire substrates, the absence of thermally induced surface reconstruction leads to the random presence of both slabs (A and B), resulting in the emergence of antiparallel domains of MoS2. This randomness raises questions about the necessity of step-edge guidance for the mono-oriented growth of MoS2. During the first phase of our JSPS基盤A research, we investigated the influence of the C3 symmetry of sapphire on the growth of MoS2. We conducted density functional theory (DFT) calculations to determine the adsorption energy of MoS2 on an ideal (0001) sapphire surface, using O-terminated surfaces confirmed by STEM. Our results showed that the adsorption energy versus orientation angle is symmetric for MoS2/sapphire heterostructures with periodic boundary conditions.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Our JSPS 基盤A research project made exceptional progress in 2023, exceeding initial expectations. The main objective was to investigate the growth mechanisms of MoS2 on commercially available sapphire substrates, focusing on sapphire's C3 symmetry and the necessity of step-edge guidance for mono-oriented growth.These findings imply that the preferred orientations of MoS2 seeds on slabs A and B are mutually opposite due to mirror symmetry, challenging the notion that surface steps alone ensure unidirectional nucleation and single-crystal growth. Instead, MoS2 tends to appear in two opposite orientations, indicating the need for a more nuanced approach to achieving mono-oriented growth. Our research has significant implications for understanding the symmetry directed epitaxy growth.
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| Strategy for Future Research Activity |
In JSPS基盤A phase 2, we will explore the kinetic (step formation and step height) and thermodynamic controls (reaction chemistry, gas flow, and surface reconstruction) that direct the mono-oriented nucleation of MoS2 flakes. If successful, we will extend the wafer-scale growth to WS2 (high mobility) and WSe2 (p-type). Meanwhile, metal oxalate-based precursors will be used to modulate the reaction chemistry, thus suppressing the formation of defect density. STEM, AFM, Raman, and low-temperature PL will be employed in concert with STM to verify the types and density of defects.
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