2019 Fiscal Year Research-status Report
Exciton physics in 1D-2D heterostructures
| Project/Area Number |
19K23593
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
Fang Nan 国立研究開発法人理化学研究所, 開拓研究本部, 基礎科学特別研究員 (50850509)
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| Project Period (FY) |
2019-08-30 – 2021-03-31
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| Keywords | carbon nanotubes / 2D materials / heterostructure / excitons |
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| Outline of Annual Research Achievements |
h-BN effects on the optical properties of carbon nanotubes (h-BN) have been investigated by performing photoluminescence (PL) spectroscopy on h-BN/CNT and CNT/h-BN heterostructures at room temperature. It has been demonstrated that CNTs directly attached to h-BN are highly luminescent with narrow linewidths of ~12 meV, which is comparable to air-suspended CNTs. The substrate quenching and broadening effects on the 2D h-BN substrates are found to be much weaker than those in conventional 3D substrates. In addition, the anomalously large redshifts in E11 and E22 of ~50 meV are observed despite the fact that h-BN has a low dielectric constant and is only attached to one side of the CNT. These findings highlight the superior properties of h-BN for 1D/2D hybrid-dimensional photonics.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The interaction between 1D CNT and 2D h-BN is strong and can be evaluated by performing photoluminescence spectroscopy. The substrate quenching and broadening effects on the 2D h-BN substrates are found to be much weaker than those in conventional 3D substrates, which is important for investigating other 1D-2D heterostructures. Large redshifts have been observed in the heterostructures due to dielectric screening effects, which has been proposed in the research plan. By performing statistical measurements on more than 400 carbon nanotubes, it has been found that the redshifts are dependent on tube diameter.The results of h-BN/CNT heterostructures have been summarized and submitted to the journal, which is under review. Arxiv version is attached as follows https://arxiv.org/abs/2003.03054.
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| Strategy for Future Research Activity |
Other 1D-2D heterostructures will be investigated. By choosing the types of 2D materials, the band alignment can be modulated. For CNT/WSe2 heterostructure, type-Ⅰ bandgap is expected. The excitons will entirely enter into the CNT, and exciton transfer from 2D WSe2 is expected. This will break the symmetry of excitons in the CNT, which could modulate the exciton binding energy. For CNT/MoS2 heterostructure, type-Ⅱ bandgap is expected. Interlayer excitons will be formed between the conduction band of MoS2 and the valance band of CNT. For the PL study of this 1D-2D heterostructure, the excitons in the 2D channel will be aligned to 1D with the same direction. Conventional exciton-exciton annihilation process in the suspended CNT is expected to be suppressed in the 1D-2D heterostructure.
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| Causes of Carryover |
I focused on the PL measurement of h-BN/CNT heterostructures in the first fiscal year. In order to fabricate more 2D-1D heterostructures, I will build the transfer system for 2D materials in the next fiscal year and continue PL measurement. Many parts such as 3D stage, zaber linear actuator need to be purchased to build up transfer system in the next fiscal year.
Moreover, the optical system needs to be optimized for the measurement of other 2D materials. The excitation wavelengths of 2D materials such as MoS2,WSe2 are different from 1D CNT, and different dichroic mirrors need to be prepared.
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