(Invited) Synthesis and Characterizations of Various Van Der Waals Hetero-Nanotubes Based on Single-Walled Carbon Nanotubes

We have successfully realized the synthesis of one-dimensional (1D) van der Waals heterostructures with single-walled carbon nanotube (SWCNT) as a template. A typical 1D heterostructure is composed of SWCNT, boron nitride nanotube (BNNT), and molybdenum disulfide nanotube (MoS₂NT), coaxially grown by serial chemical vapor deposition (CVD) steps [1]. Isolated SWCNTs, BN-CVD at high temperatures such as 1100 °C from ammonia borane, and MoS₂-CVD from MoO₃ and Sulfur are original key requirements. Recently, we have achieved the additional CVD growth of carbon nanotubes from ethanol-CVD. We can remove SWCNT from SWCNT@BNNT by gentle oxidation process because BNNT is thermally more stable than SWCNT [2]. By comparing optical properties of BNNT@MoS₂NT and SWCNT@BNNT@MoS₂NT, we found the strong photoluminescence (PL) from monolayer MoS₂NT of BNNT@MoS₂NT and the exciton energy transfer between SWCNT and MoS₂NT through thin BNNT for SWCNT@BNNT@MoS₂NT [2]. We expect to prove the inter-tube excitons from the ultrafast optical spectroscopy [3]. We can realize various hetero-nanotubes in different morphologies such as SWCNT thin film, pillar-suspended SWCNT, chirality separated SWCNT deposited on TEM grid, and bulk SWCNTs grown on zeolite-supported catalysts [4]. Simply with SWCNT@BNNT in a thin film form, the enhanced thermal conductance [5] is very promising for macroscopic applications of heterostructures. Because BNNT coating over SWCNT film will not influence the transparency in the visible range, those films are immediately applicable for a saturable absorber in mode-lock fiber lasers. In order to fabricate a practical electronic or optoelectronics devices, micro-meter long 1D van der Waals heterostructure SWCNT@BNNT@MoS₂NT were prepared between Si pillars. After transferring to SiO₂ substrates and fabricating metal electrodes, we have examined various device characteristics. The naturally p-doped SWCNT and n-type MoS₂NT becomes a radial semiconductor–insulator–semiconductor (S-I-S) heterojunction diode [6]. Optoelectronic and electronic properties of such devices will be discussed.

Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.

References:

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