文献阅读:08

标题:One-Dimensional van der Waals Heterostructures
作者:Rong Xiang, Taiki Inoue, Yongjia Zheng, Akihito Kumamoto, Yang Qian, Yuta Sato, Ming Liu, Daiming Tang, Devashish Gokhale, Jia Guo, Kaoru Hisama, Satoshi Yotsumoto, Tatsuro Ogamoto, Hayato Arai, Yu Kobayashi, Hao Zhang, Bo Hou, Anton Anisimov, Mina Maruyama, Yasumitsu Miyata, Susumu Okada, Shohei Chiashi, Yan Li, Jing Kong, Esko I. Kauppinen, Yuichi Ikuhara, Kazu Suenaga and Shigeo Maruyama
期刊:Science
日期:2020

简介:这是一篇关于一维异质结的文献,标题为“一维范德华异质结”。大致翻译了一下,翻译仅供参考,请以原文为准。如翻译有不妥之处,欢迎一起讨论。

摘要

We present the experimental synthesis of one-dimensional (1D) van der Waals heterostructures, a class of materials where different atomic layers are coaxially stacked. We demonstrate 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. We also report 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. This work suggests that all of the materials in the current 2D library could be rolled into their 1D counterparts and a plethora of function-designable 1D heterostructures could be realized.

作者提出了一维(one-dimensional,1D)范德华(van der Waals)异质结的实验合成方法,这种异质结是一类不同原子层共轴堆积的材料。作者展示了在单壁碳纳米管(single-walled carbon nanotube,SWCNT)上生长六角氮化硼(hexagonal boron nitride,BN)和二硫化钼(MoS2)单晶体层的过程。对于后者而言,它更容易克服应变效应从而合成大直径纳米管。作者还报道了一种由内部 SWCNT、中间三层 BN 纳米管和外部 MoS2 纳米管组成的直径达 5 纳米的异质结。通过电子衍射可以验证异质结中所有的壳层都是单晶。这项工作表明,2D 数据库中所有的材料都可以卷成 1D 材料,由此可以实现大量的功能可设计的 1D 异质结。

前言

The demonstration of two-dimensional (2D) van der Waals (vdW) heterostructures[1–3]—in which atomic layers are stacked on each other and different 2D crystals are combined beyond symmetry and latticematching—represents a way of manipulating crystals to enable both the exploration of physics not observable in conventional materials and device applications.[4–8] These 2D heterostructures have been fabricated by transferring preprepared layers (transfer approach)[5, 9] or by synthesizing layers onto a base layer (synthesis approach).[10] Whether such artificial materials and interfaces can be fabricated in other dimensions remains an open question. In 1D materials, for example, an ideal vdW heterostructure would be a coaxial structure with different types of nanotubes. Such ideal structures have been investigated in theoretical studies[11, 12] and would appear to require a synthesis approach. However, experimental attempts to fabricate coaxial nanotube structures have yielded only amorphous or very poorly crystallized coatings.[13, 14]

二维(two-dimensional,2D)范德华(van der Waals,vdW)异质结[1–3]-其中原子层彼此堆叠,不同的 2D 晶体组合在一起而不用考虑对称性和晶格匹配-代表了一种晶体的利用途径,可以用来探究传统材料中无法观测到的物理现象以及应用到器件中[4–8]。我们通过转移预处理层(转移方法)[5, 9]或者在基层上合成另外的层(合层方法)[10]来制备这些 2D 异质结。在其它维度是否也可以制造这种人造材料和界面仍然是个悬而未决的问题。例如,在 1D 材料中,一个理想的 vdW 异质结将会是由不同类型的纳米管组成的同轴结构。理论研究已经对这种理想的结构进行了研究[11, 12],但仍然需要一种合成方法来制备这些结构。有人尝试用实验方法制备同轴的纳米管结构,然而只得到了无定形的或者结晶度非常低的涂层[13, 14]

We demonstrate the experimental discovery and controlled fabrication of true 1D vdW heteronanotubes. A typical structure was $4$ to $5\ \rm{nm}$ in diameter but contained three different shells: an inner carbon nanotube (CNT), a middle hexagonal boron nitride nanotube (BNNT), and an outer molybdenum disulfide (MoS2) nanotube. Electron diffraction (ED) and many other characterizations were used to confirm that each shell in this structure was a seamless, perfect nanotube that realized the heteronanotubes studied in theoretical models. The heterostructures formed through an open-end growth mode that has rarely been observed in previous 1D nanostructure growth. We outline some basic geometric principles that governed the formation of these 1D vdW heterostructure nanotubes, including the absence of structural correlation between inner and outer shells and the requirement of a threshold diameter for MoS2 nanotubes.

作者展示了真实 1D vdW 异质纳米管的实验发现和可控制备过程。一个典型的结构是直径 $4$ 到 $5\ \rm{nm}$ 但包含三种不同的壳层:内层是碳纳米管(carbon nanotube,CNT),中间是六角氮化硼纳米管(hexagonal boron nitride nanotube,BNNT),外部是二硫化钼(molybdenum disulfide,MoS2)纳米管。作者使用电子衍射(electron diffraction,ED)和许多其他的表征方法来验证这个结构中的每个壳层都是无缝的、完整的纳米管,实现了理论模型中所研究的异质纳米管。这种异质结构是通过开放式生长模式形成的,这种模式在以往的一维纳米结构生长中很少观察到。作者概述了一些能够控制 1D 异质结纳米管形成的基本几何原理,包括内外壳层之间没有结构相关性,以及对 MoS2 纳米管阈值直径的要求。

In this study, the base structure, a singlewalled carbon nanotube (SWCNT),[15] was chosen as the starting material for several reasons. It is, so far, the best-studied 1D material and can be synthesized in many controlled geometries. Also, a SWCNT can be metallic or semiconducting, which means it could serve as the electrode or channel material for a heteronanotube device. The typical SWCNTs used in this study were $1$ to $2\ \rm{nm}$ in diameter and a few micrometers in length and were self-suspended as a random network.[16] Schematics comparing the 2D and 1D vdW heterostructures are presented in Fig. 1, A and B.

本研究选择基础结构,即单壁碳纳米管(singlewalled carbon nanotube,SWCNT)[15],作为起始材料有多种原因。到目前为止,它是研究得最好的一维材料,可以在许多可控的几何结构中合成。此外,SWCNT 可以是金属的或半导体,这意味着它可以作为异质纳米管器件的电极或通道材料。在这项研究中使用的典型 SWCNT 直径为 $1$ 到 $2\ \rm{nm}$,长度为几微米,并且能够自悬浮形成一个随机网格结构[16]。图 1 A 和 B 中的示意图对 2D 和 1D vdW 异质结进行了对比。

图表

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<b>Figure 1</b>. Overview of 1D vdW heterostructures. (A and B) Atomic arrangement of two-dimensional planar vdW heterostructures (A) and one-dimensional coaxial vdW heterostructures (B). (C and D) TEM image (C) and structure models (D) of a SWCNT wrapped with two layers of BNNT. (E) Aberration-corrected TEM image of a SWCNT-BNNT and its fast Fourier transform. (F) Annular dark-field (ADF) image and EELS mapping of a SWCNT partially wrapped with BNNT, showing that the inner layer is carbon and the outer layer is BN. C K, K<sub>1</sub> edge of C (green); B K, K<sub>1</sub> edge of B (cyan); N K, K<sub>1</sub> edge of N (red).
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<b>图 1</b>. 一维 vdW 异质结概述。(A 和 B)二维平面 vdW 异质结(A)和一维同轴vdW异质结(B)的原子排列。(C 和 D)两层 BNNT 包裹的 SWCNT 的 TEM 图像(C)和结构模型(D)。(E)SWCNT-BNNT 的像差校正 TEM 图像及其快速傅里叶变换。(F)部分包裹 BNNT 的 SWCNT 的环形暗场(annular dark-field,ADF)图像和 EELS 图表明,其内层为碳,外层为 BN。C K, K<sub>1</sub> 边缘(绿色);B K, K<sub>1</sub> 边缘(青色);N K, K<sub>1</sub> 边缘(红色)。
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<div><q>
<b>Figure 2</b>. Structural characterization of SWCNT-BNNT vdW heterostructures. (A and B) Atomic model (A) and TEM image (B) of SWCNT-BNNT atomic steps. (C) Experimental (Exp) and simulated (Sim) ED pattern of the inner<sup>[17, 13]</sup> SWCNT and outer<sup>[33, 3]</sup> BNNT. (D) Plot of chiral angle of inner SWCNT versus the outer BNNT for double-walled SWCNT-BNNT, revealing that as-grown SWCNTs were enriched in the near-armchair form but that the outer BNNT was evenly distributed.
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<b>图 2</b>. SWCNT-BNNT vdW 异质结的结构表征。(A 和 B)SWCNT-BNNT 原子台阶的原子模型(A)和 TEM 图像(B)。(C)内侧<sup>[17, 13]</sup> SWCNT 和外侧<sup>[33, 3]</sup> BNNT 的实验(Exp)和模拟(Sim)ED 图案。(D)双壁 SWCNT-BNNT 的内侧 SWCNT 与外侧 BNNT 的手性角图显示,生长的 SWCNT 在近扶手椅状结构中富集,但外侧 BNNT 分布均匀。
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<div><q>
<b>Figure 3</b>. Optical, thermal, and electronic characterization of SWCNT-BNNT heterostructures. (A) Typical G band of an individual SWCNT before and after BN coating. Arb. units, arbitrary units; dotted line indicates the original G band position at $\sim 1590\ \rm{cm^{−1}}$. (B) PL excitation-emission map of suspended<sup>[9, 8]</sup> SWCNT after BN CVD. Circle and triangle marks indicate the optical transition energy of suspended<sup>[9, 8]</sup> SWCNT in the ambient atmosphere<sup>[38, 39]</sup> and in vacuum.<sup>[40]</sup> (C) Thermal stability of SWCNT and SWCNT-BNNT heterostructures obtained in an in situ Raman reaction cell. The ratio of G-band intensity (G<sub>i</sub>) after high-temperature burning to the original G-band intensity (G<sub>o</sub>) before burning gives the relative loss of SWCNTs in these samples. (D to F) A schematic (D), AFM image (E), and characteristic transfer curve (F) of a back-gated FET built on a SWCNT-BNNT. $I_{\rm{DS}}$, drain current; $V_{\rm{GS}}$, gate voltage; $V_{\rm{DS}}$, drain voltage. (G) Schematic of the transport measurement inside TEM. (H) Bright-field TEM image (upper) and resistance versus number of BN layers (lower). (I) Typical $I$-$V$ curve obtained in electronic measurement inside TEM.
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<b>图 3</b>. SWCNT-BNNT 异质结的光、热和电子特性。
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<div><q>
<b>Figure 4</b>. SWCNT-MoS<sub>2</sub> 1D vdW heterostructure. (A to C) Atomic model (A), HRTEM image (B), and high-angle annular dark field (HAADF) STEM image (C) of a singlewalled MoS<sub>2</sub>nanotube grown on a SWCNT. (D) Strain energy of a single-walled MoS<sub>2</sub> nanotube as a function of tube diameter, calculated by a modified Stillinger-Weber (SW) potential and density functional theory (DFT) simulation.
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<b>图 4</b>. SWCNT-MoS<sub>2</sub> 1D vdW 异质结。
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<div><q>
<b>Figure 5</b>. SWCNT-BNNT-MoS<sub>2</sub> 1D vdW heterostructures. (A to D) Atomic model (A), HAADF-STEM image (B), annular bright field (ABF)–STEM image (C), and EELS mapping (D) of a $5\ \rm{nm}$–diameter ternary 1D vdW heterostructure, consisting of one layer of carbon, three layers of BN, and one layer of MoS<sub>2</sub>. Scale bars, $5\ \rm{nm}$; S L, L2,3 edge of S (yellow). (E) An almost-ideal experimental ED pattern of a SWCNT-BNNT-MoS<sub>2</sub> heterostructure, with different colors distinguishing the diffractions from different layers (L1 green, SWCNT; L2 blue, BNNT1; L3 red, BNNT2; and L4 yellow, MoS<sub>2</sub> nanotube). (F) Optical images of SWCNT, SWCNT-BNNT, and SWCNT-BNNT-MoS2 films against a printed logo of the University of Tokyo. Scale bar, $10\ \rm{mm}$.
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<b>图 5</b>. SWCNT-BNNT-MoS<sub>2</sub> 1D vdW 异质结。
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结论

We have extended the concept of vdW heterostructures to 1D materials. In these coaxial heteronanotubes, both cores and shells are single crystalline and form a seamless structure. We showed the controlled fabrication of SWCNT-BNNT and SWCNT-BNNT-MoS2 coaxial structures with diameters $\lt 5\ \rm{nm}$. We also developed some basic rules governing the fabrication of 1D heterostructures, including the absence of shell-shell epitaxial structure correlation and the requirement of a threshold diameter for MoS2 nanotubes. This approach is likely extendable to other layered materials[35–37] and yields a large number of combinations, and 1D vdW heterostructures could host distinctive physics arising from curvature and diameter confinement.

作者将 vdW 异质结的概念扩展到了 1D 材料。在这些同轴异质纳米管中,核和壳都是单晶并形成一个无缝的结构。作者展示了直径 $\lt 5\ \rm{nm}$ 的 SWCNT-BNNT 和 SWCNT-BNNT-MoS2 同轴结构的可控合成方法。作者也发展了一些控制 1D 异质结合成的基本规则,包没有括壳-壳外延结构的相关性,以及对 MoS2 纳米管阈值直径的要求。这种方法有可能扩展到其他的层状材料中[35–37]并产生多种组合方式,同时 1D vdW 异质结可能伴随有由曲率和直径限制引起的独特物理现象。

文章作者: 喵函数
文章链接: https://eigenmiao.site/2020/03/20/article-08/
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