| 研究実績の概要 |
1. One-dimensional (1D) van der Waals heterostructure is successfully synthesized by chemical vapor deposition (CVD). We demonstrated the growth of single-crystal layers of hexagonal boron nitride (BN) and molybdenum disulfide (MoS2) crystals on single-walled carbon nanotubes (SWCNTs). For the latter, larger-diameter nanotubes that overcome strain effect were more readily synthesized. The chiral angle of the outer BN nanotube is found to be independent of the inner SWCNTs. We also obtained a 5-nanometer diameter heterostructure consisting of an inner SWCNT, a middle three-layer BN nanotube, and an outer MoS2 nanotube. Electron diffraction verifies that all shells in the heterostructures are single crystals. Because of the wrapping of BNNT increases the diameter of the whole structure, the yield of MoS2 nanotube is significantly improved, reaching about 10% on suspended and isolated SWCNTs. This work suggests that a plethora of function-designable 1D heterostructures could be realized.
2. To understand the growth mechanism of BN nanotubes on SWCNTs, we demonstrate the heteroepitaxial growth of aligned monolayer h-BN single-crystals on exfoliated graphite by CVD without a metal catalyst. Triangular shaped domains were aligned with each other, which suggests the epitaxy between h-BN and the underlying graphite. Characterizations confirmed that the h-BN/graphite samples were of high quality. A growth kinetics study over different temperatures indicated an increase in the growth rate at high temperature.
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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
We have proven the existence of one-dimensional van der Waals heterostructures, and demonstrated an experimental approach to synthesize SWCNT-BN, SWCNT-MoS2, and SWCNT-BN-MoS2 heterostructures. Mostly importantly these shells in a heterostructure are single crystals, as confirmed by electron diffraction in a TEM. This makes the structure as ideal as what has been demonstrated in theoretical studies. Our results not only confirm a class of new material, but also suggest the current 2D materials may be all rolled into their 1D counterparts. The main result of this project is published (Science, (2020), vol. 367, pp. 537-542).
This work is also highlighted in the same issue of Science Journal (Science 2020, 367, 6477, 506-507), Nature Electronics (Nature Electronics, 2020, 3, 73), and other media.
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| 今後の研究の推進方策 |
Future work will be focused on the next two parts.
1. To understand the growth mechanism and the crystal epitaxial relationship of 1D van der Waals heterostructures. TEM will be used to characterize the growth position, and to identify the structures of different shells. We expect a systematic understanding on the open-end growth model, non-catalytic growth mechanism and the growth dynamics.
2. To investigate the new phenomena and properties in this new structure. We expect to understand the effect of BN on the thermal and optical properties of the inner SWCNTs. We also expect to investigate the optical response of the outer small diameter MoS2 nanotube. In addition, field effect transistor will be fabricated to understand the electronic properties of the heterostructures.
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