| 研究実績の概要 |
Recent finding of high-temperature two dimensional (2D) superconductivity above 100 K opens up a fascinating new research direction towards pursuing high Tc superconductors and understanding the underlying new physics. The extensive study of this new field strongly relies on the growth of 2D layered metallic systems. Synthetic preparation of 2D metallic systems, however, is not straightforward probably because of the stronger interlayer interaction, which is in stark contrast to the well-developed synthetic technique of 2D layered semiconductors such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), etc. We report here the first successful growth of a new 2D metallic transition metal dichalcogenides (TMDCs), 3R-NbS2, which exhibits superconductivity and charge-density-wave (CDW) phases in bulk counterparts, down to the thinnest form (3 layers). Our as-grown samples were directly synthesized on top of hBN substrates, showing fairly sharp triangular or hexagonal shapes. The Raman bands show systematic shifts depending on the layer numbers while the optical contrasts show strong layer number dependence both of which can be served as signatures for layer number identification. Our transport data demonstrate that 3R-NbS2 down to the thinnest form still preserve its metallic nature. Our work demonstrates the first time growth of metallic TMD system, opening up a new synthetic avenue for controllable growth of 2D layered metallic materials. The work reported here will have a big impact in studying the rich physics of 2D metallic TMDs materials.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
I have finished the manuscript regarding the research of NbS2 synthesis and characterization which will be submitted to SCI journals shortly. In addition to that, I have already started several research work even before the ending of this fiscal year for which I claimed that I have achieved more than what I and my supervisor expected. This year research work greatly improved my research ability when I directly participated in the direction/instruction of two B4 undergraduates. Working together with my supervisors, I have been giving my own idea and solutions to their research activities. We had a very good team-work in where I am a team leader under the supervision of my professors. We already prepared the manuscript of one of the research topics. I believe that we will have more research results in the near future.
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| 今後の研究の推進方策 |
1. Experimental demonstration of valley-related physics in TMDCs: e.g., Valley-Hall effect on CVD-synthesized monolayer TMDCs Strategy: Circularly-polarized light + micro-sized device fabrication (by electron beam lithography) + CVD sample preparation + electrical measurement compatible with cryostat
2. Exploration of exciton formation in metallic 2D systems Strategy: Molecular beam eptitaxy (MBE) growth of metallic 2D layers + optical absorption/reflection measurement
3. Valley-related excitons in 2D TMDC heterostructures Strategy: Molecular beam eptitaxy (MBE) growth of 2D heterostrcutures + structure characterization (stacking manners) + circularly-polarization-resolved optical pumping and detection
4. Interlayer interaction in van der Waals coupled 1D systems (e.g., double-wall carbon nanotubes (DWCNTs)) which is a following work of my previous paper whlist keeping close collaboration with theorists Strategy: CVD growth of individual DWCNTs + structure determination (by electron beam diffraction) + electrical transport and optical measurement
5. Doping-induced phase control and mobility enhancement of semiconducting molecular crystals by utilization of hBN Strategy: Molecular crystal growth by thermal deposition + preparation of field-effect transistor structures + transport measurement with EDLT doping (large amount of carriers)
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