Liu Ming, Hisama Kaoru, Zheng Yongjia, Maruyama Mina, Seo Seungju, Anisimov Anton, Inoue Taiki, Kauppinen Esko I, Okada Susumu, Chiashi Shohei, Xiang Rong, Maruyama Shigeo
Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571, Japan.
ACS Nano. 2021 May 25;15(5):8418-8426. doi: 10.1021/acsnano.0c10586. Epub 2021 Apr 21.
Single-walled and multiwalled molybdenum disulfide (MoS) nanotubes have been coaxially synthesized on small-diameter boron nitride nanotubes (BNNTs) that are obtained from removing single-walled carbon nanotubes (SWCNTs) in heteronanotubes of SWCNTs coated by BNNTs. The photoluminescence (PL) from single-walled MoS nanotubes supported by core BNNTs is observed in this work, which evidences the direct bandgap structure of single-walled MoS nanotubes with a diameter around 6-7 nm. The observation is consistent with our DFT results that the single-walled MoS nanotube changes from an indirect-gap to a direct-gap semiconductor when the diameter of a nanotube is more than around 5.2 nm. On the other hand, when there are SWCNTs inside the heteronanotubes of BNNTs and single-walled MoS nanotubes, the PL signal from MoS nanotubes is considerably quenched. The charge transfer and energy transfer between SWCNTs and single-walled MoS nanotubes were examined through characterizations by PL, X-ray photoelectron spectroscopy, and Raman spectroscopy. Moreover, the PL signal from multiwalled MoS nanotubes is significantly quenched. Single-walled and multiwalled MoS nanotubes exhibit different Raman features in both resonant and nonresonant Raman spectra.
单壁和多壁二硫化钼（MoS）纳米管已在小直径氮化硼纳米管（BNNTs）上同轴合成，这些氮化硼纳米管是通过去除由BNNTs包覆的单壁碳纳米管（SWCNTs）的异质纳米管中的单壁碳纳米管而获得的。在这项工作中观察到了由核心BNNTs支撑的单壁MoS纳米管的光致发光（PL），这证明了直径约为6-7nm的单壁MoS纳米管的直接带隙结构。该观察结果与我们的密度泛函理论（DFT）结果一致，即当纳米管直径大于约5.2nm时，单壁MoS纳米管从间接带隙半导体转变为直接带隙半导体。另一方面，当BNNTs和单壁MoS纳米管的异质纳米管内部存在SWCNTs时，MoS纳米管的PL信号会显著淬灭。通过PL、X射线光电子能谱和拉曼光谱表征研究了SWCNTs与单壁MoS纳米管之间的电荷转移和能量转移。此外，多壁MoS纳米管的PL信号也显著淬灭。单壁和多壁MoS纳米管在共振和非共振拉曼光谱中表现出不同的拉曼特征。
