Isolation of Single-Wired Transition-Metal Monochalcogenides by

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Isolation of Single-Wired Transition-Metal Monochalcogenides by Carbon Nanotubes Masataka Nagata, Shivani Shukula, Yusuke Nakanishi, Zheng Liu, Yung-Chang Lin, Takuma Shiga, Yuto Nakamura, Takeshi Koyama, Hideo Kishida, Tsukasa Inoue, Naoyuki Kanda, Shun Ohno, Yuki Sakagawa, Kazu Suenaga, and Hisanori Shinohara Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b05074 • Publication Date (Web): 24 Feb 2019 Downloaded from http://pubs.acs.org on February 25, 2019

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a

b

c

Decomposition & Sublimation Bulk MoTe2

4.4 Å

Self-assembly

4.8 Å

CNT + MoTe2 MoTeNW

d

e

ACS Paragon Plus Environment

f

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a Bulk MoTe MoTeNW@CNTs

b Empty CNTs

c

d

Empty CNTs

Raman Intensity / arb. units

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×15

MoTeNW@CNTs

×15 MoTeNW@CNTs 100

150

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Raman Shift / cm-1


250

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a

α

b α = 30°

c α = 30°

α = 15° α = 15°

α = 0°

α = 0°


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40

a

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b

1.3 nm XPS Intensity / arb. units

1.27 nm 30 25 20 15 10

900 °C

1100 °C

MoTe 1200 °C

5 0

Te

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

580

578

Diameter of CNTs / nm

d

Oxidized MoTe2 MoTeNW

Evaporation

XPS Intensity / arb. units

Oxidation

574

572

570

Binding Energy / eV

c MoTe2

576

e

Mo 3d

MoO3

MoTe2 Mo2O5 MoO2

Vapor Reaction

240

Te & MoOx （Gas）

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Binding Energy / eV


225

Raman Intensity / arb. units

Abundance

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* *

MoTe2

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Isolation of Single-Wired Transition-Metal Monochalcogenides by Carbon Nanotubes Masataka Nagata,1, ‡ Shivani Shukla,2, ‡ Yusuke Nakanishi,*1, 3, 4 Zheng Liu,*5, 6 Yung-Chang Lin,6 Takuma Shiga,7 Yuto Nakamura,8 Takeshi Koyama,8 Hideo Kishida,8 Tsukasa Inoue,1 Naoyuki Kanda,1 Shun Ohno,9 Yuki Sakagawa,10 Kazu Suenaga,6 and Hisanori Shinohara*1, 3 1. Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan. 2. Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, USA. 3. Institute for Advanced Research, Nagoya University, Nagoya 464-8602, Japan. 4. Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan. 5. National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560, Japan. 6. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan. 7. Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan. 8. Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan. 9. Gifu High School, Gifu 500-8889, Japan. 10. Ichinomiya High school, Ichinomiya 491-8533, Japan.

KEYWORDS: Transition-metal monochalcogenides, One-dimensional van der Waals materials, Template synthesis, Nanotubes, Atomic-resolution transmission electron microscopy


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ABSTRACT

The successful isolation of single-layers from two-dimensional (2D) van der Waals (vdW)layered materials has opened new frontiers in condensed matter physics and materials science. Their discovery and unique properties laid the foundation for exploring 1D counterparts. However, the isolation of 1D vdW-wired materials has thus far remained a challenge, and effective techniques are demanded. Here we report the facile synthesis of isolated transitionmetal monochalcogenide MoTe nanowires by using carbon nanotubes (CNTs) as molds. Individual nanowires are perfectly separated by CNTs with a minimal interaction, enabling detailed characterization of the single-wires. Transmission electron microscopy revealed unusual torsional motion of MoTe nanowires inside CNTs. Confinement of 1D vdW-wired materials to the nano-test-tubes might open up possibilities for exploring unprecedented properties of the nanowires and their potential applications such as electromechanical switching devices.

MAIN TEXT Introduction Since the advent of graphene in the 2000s, 2D materials have been at the forefront of nanoscience and nanotechnology. Oftentimes, vdW-layered materials with one or a few layers can exhibit superlative electronic properties compared to their bulk counterparts. Over the last decade, 2D vdW-layered structure has led to the exploration of many inorganic ‘post-graphene’ materials, such as hexagonal boron-nitrides, black-phosphorous, III-VI semiconductors, and transition-metal dichalcogenides (TMDs), revealing new fundamental physics and potential for future applications in various fields ranging from electronics to catalysts.1, 2


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In contrast, dropping down one notch in dimensionality, from 2D vdW-layered to 1D ‘vdWwired’

materials,

has

proven

a

challenging

step

for

researchers.

Transition-metal

monochalcogenides (TMMs) are one of the 1D vdW-wired materials that are difficult to chemically isolate. For example, molybdenum monochalcogenides are regarded as building blocks of superconducting Chevrel-phase bulk materials, AxMo6X6 quasi-1D compounds surrounded by alkali-metal ions.3 Atomically precise 1D TMMs possess a distinct advantage as compared with structurally ambiguous 1D carbon materials, and have intensively been studied by experiments and theory.4–9 Early studies reported successful syntheses of MoS and MoSe by using chemical,10,

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epitaxial,12 and lithographic methods.13 Very recently, MoTe was also

successfully fabricated by vacuum annealing of bulk MoTe2.14–16 In most cases, however, the previously reported TMMs existed in a mixture with bulk TMDs, or in bundles, hindering characterization of their individual properties. Theoretically, isolated single-wires of some TMMs could possess electronic properties distinct from their bulk counterparts,15, 17 although this has never been fully verified by experiments. The reliable production of single-wired TMMs still remains a significant challenge to researchers seeking to illuminate the nature and potential applications of the vdW-wired materials. Here we report the template-based synthesis of single-wired MoTe inside carbon nanotubes (CNTs). Chemically and thermally robust CNTs act as ‘nano-test-tubes’ for the synthesis of unusual nanomaterials, while the nanotube itself is not involved in the reactions.18–20 The 1D confinement at the nanoscale instigates the self-assembly of MoTe nanowires (MoTeNWs) similar to other 1D materials such as ladder-like inorganic helixes,21 ultra-narrow graphene nanoribbons,22 and atomic sp1-carbon chains (carbynes).23 Furthermore, the sheaths of CNTs form few covalent bonds with inner products, instead providing a shield against oxidation. Their


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inert functionality allows easy handling and accurate characterization of the as-produced wires for future technological advancements. This bottom-up synthesis approach offers better control over the nanoscale properties of 1D vdW-wired materials compared to previously reported topdown methods.

Results & Discussion MoTeNWs was synthesized by vacuum annealing of MoTe2 bulk crystals in the presence of open-ended CNTs above 1000 °C (Figure 1a). Figure 1b presents a typical high-angle annular dark-field scanning transmission electron microscopy (STEM) image of MoTeNWs confined inside CNTs. The heavier Te atoms appear brighter than Mo atoms, as verified by the simulated image (enclosed in the yellow rectangle in Figure 1b inset). As illustrated in Figure 1c, MoTeNWs are quasi-1D materials comprised of alternately stacked Mo3Te3 triangles along the nanowire growth axis. Notably, the outermost atoms along the axial direction of the nanowires are always Te atoms, demonstrated by electron energy loss spectroscopy (EELS) chemical map of an isolated MoTeNW at an atomic-level shown in Figure 1d. The stoichiometry of the nanowires was deduced to show a 1:1 atomic ratio of Mo/Te from EELS analyses. The measured lattice constants parallel and perpendicular to axial direction of the nanowires are 4.4 Å and 4.8 Å, respectively (Supplementary Figure 1), which are similar to corresponding values of other TMMs isolated by the lithographic method.13 Lower-magnification high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation and Cs-corrected TEM images (Supplementary Figure 2) revealed that uniformly structured MoTeNWs formed inside CNTs have a high-yield (Figure 1e, f).


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Surface chemical states of MoTeNWs encapsulated inside CNTs were analyzed by using high-resolution X-ray photoelectron spectroscopy (XPS). As displayed in Figure 2a, the XPS Te-3d core-levels spectrum of the samples, which were sufficiently washed with H2SO4 prior to measurement, shows the Te-3d5/2 and Te-3d3/2 peaks at binding energies of 572.6 and 582.9 eV, respectively. Compared to bulk MoTe produced outside CNTs (572.9 and 583.2 eV), binding energies of the encapsulated MoTeNWs are lying on the similar range of their bulk counterparts, indicating minimal electron interaction between the NWs and CNTs. This is also evidenced by the fact that the C-1s peak in the host CNTs exhibits little change (blue-shift by only 0.3 eV), as shown in Figure 2b. Moreover, the peaks associated with Te oxides (576.4 and 586.8 eV) in MoTeNW@CNTs exhibit much weaker intensities than the corresponding peaks of bulk, residual MoTe clinging to the outer walls of CNTs. This suggests that inner MoTeNWs are fully protected by CNTs, preventing oxidation (Figure 2a and Supplementary Figure 3a). Chemical XPS analysis reveals that chemically inert nano-test-tubes stabilize and protect single MoTeNWs, facilitating detailed characterization. The nanowire formation was further confirmed by Raman scattering spectra obtained before and after vacuum annealing as shown in Figure 2c. Raman spectra of both samples in the range of 150–200 cm–1 are dominated mainly by radial breathing modes (RBM) of CNTs,24 while a prominent peak can be observed at 255 cm–1 only in the encapsulating samples. Previous literature does not assign this peak to either empty CNTs or the bulk precursor MoTe2.25 Earlier studies observed a Raman signal of bundled MoTeNWs at around 250 cm–1.14,

16

Thus, it is

reasonable to assign the peak observed at 255 cm–1 to the MoTeNWs formed inside CNTs. This is the first observation of Raman vibration modes of isolated MoTeNWs. Similarly, the Raman peaks originated from HgTe nanowires formed inside CNTs were reported.26 Considering that


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bundled MoTeNWs exhibit a signal around 150 cm–1, the spectral changes in the RBM region may arise from the encapsulation of MoTeNWs. However, quantitative analyses of this region were severely hindered by inhomogeneous distribution of the chirality of CNTs employed in this work. Characterization of the Raman vibrational mode still needs further investigation. To get insight into the peak attributed to isolated MoTeNWs, we performed first-principlesbased phonon calculation for an isolated MoTeNW. Considering only totally symmetric modes from the MoTeNW structure and eigenmode, Ag mode with the frequency of 261 cm–1 is in close agreement with Raman scattering measurements. The corresponding mode has a RBM of molybdenum cores, which is illustrated in Figure 2d and Supplementary movie. Further analyses from HAADF-STEM images revealed a unique mechanical flexibility of single MoTeNWs. The MoTeNWs confined within CNTs can be bent and twisted, similar to single MoS and MoSe nanowires produced by electron-beam etching of TMD monolayers.13,

27, 28

During STEM

observation, MoTeNWs were oftentimes found to rotate inside CNTs, as illustrated in Figure 3a. A single MoTeNW can be divided into several segments (2–4 nm), with each section displaying a different rotation angle around the chain axis. The atomic planes in each segment share the same normal vector. However, each segment appears to be rotated approximately 15 degrees from the neighboring segments (Figure 3b), as shown in Figure 3c where simulated images are generated using the corresponding models. Such discontinuous torsional motion differs largely from the continuous twisting motion found in the electron-beam etched MoS nanowire previously reported.27 Very recently, Pham et al reported that NbSe3 chains confined within carbon/boron nitride nanotubes, in which Nb atoms are bridged by a set of three Se atoms (trigonal prism),29 also exhibited continuous, torsional motion.30 Interestingly, such discontinuous torsional motions have never been reported even in close-packed MoTe bulk crystals (bundled MoTeNWs). The cause for the unique torsions requires further investigations.


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MoTeNWs are selectively grown inside CNTs when the diameters of the nanotubes and MoTeNWs fit properly with each other. A histogram of the diameters of CNTs containing MoTeNWs obtained from Cs-corrected TEM observation is illustrated in Figure 4. A narrow distribution of diameters of CNTs (1.3 ± 0.1 nm) filled with MoTeNWs indicates the importance of spatial confinement in stabilizing and assisting the growth of MoTeNWs. We hypothesized that vdW interaction between the NWs and well-fitting CNTs allows for higher thermodynamic stability, compared to the CNTs with larger diameters. Previously, similar diameter-selective CNT-templated growth has been observed in diamond nanowires,31 graphene nanoribbons,32 and silicon-based nanowires.33 The well-fitting 1D reaction vessel confines chemical reactions to one direction, where epitaxial growth is likely to proceed along the inner walls of CNTs. Owing to the growth-promoting effect, the nanowires orient along the axis of CNTs with lengths on the sub-micron scale (Supplementary Figure 4). Moreover, the nanowires are protected by CNTs to form with very few Te vacancies. Further XPS analysis revealed that nanowires formation is strongly dependent on the annealing temperature (Figure 4b). Te-3d5/2 spectra of samples annealed at 900, 1100, and 1200 °C show a shift in predominant signals that mirrors the evolution of chemical reactions occurring inside the nano-test-tubes. At 900 °C, above the bond dissociation temperature of MoTe2,34 the signal is dominated by the signature of TeNWs (Supplementary Figure 3b). TEM and energy dispersive X-ray (EDX) data of the sample produced at 900 °C is shown in Supplementary Figure 5a, in which encapsulating CNTs are predominantly filled with TeNWs. After annealing above 1100 °C, the yield of MoTeNWs was significantly increased with increasing temperature, which was also demonstrated by TEM/EDX analyses (Supplementary Figure 5b). Besides MoTe2, other MX2 crystals i.e., MoS2, MoSe2, and WTe2 were also investigated as


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precursors for nanowire formation under the same conditions. Bulk MoS2 and MoSe2 remained largely intact without any nanowires formation (Supplementary Figure 6a, b). When the experiment was conducted using WTe2, only TeNWs were observed (Supplementary Figure 6c). These findings can be explained by examining the high-temperature behavior of each precursor in a vacuum. The bond dissociation temperatures of MoS2 and MoSe2 are higher than that of MoTe2 and WTe2, due to the increased dissociation enthalpies of M−X bonds.34,

35

According to early studies, bond dissociation results in the formation of solid metals with X atoms and X2 molecules in vapors.36, 37 At the present range of temperatures studied, the vapor pressure of the respective chalcogen from MoS2 and MoSe2 is lower than that of tellurium from MoTe2/WTe2, and hence the production yield of nanowires (even pure chalcogen nanowires) is significantly decreased. Most significantly, the MoTe2 precursor uniquely produces MoTeNWs due to its reactivity with oxygen. We propose a possible mechanism for nanowire formation (Figure 4c) below:

MoTe2 → MoTe2/MoOx → MoTeNWs + TeO2 Oxidization

Tellurization

Compared to MoS2 and MoSe2, MoTe2 and WTe2 are more reactive with oxygen.38,

39

Oxidization of MoTe2 precursors was confirmed by XPS and Raman analyses (Figure 4d, e). The intermediate oxides are sometimes volatile at the present temperatures, as is the case with MoO3 and MoO2.40 Thus, while the vaporization of Mo atoms proved to be a barrier to nanowire formation for MoS2 and MoSe2 precursors, Mo atoms readily sublime when using MoTe2. The nanowires were possibly produced when MoOx and pure tellurium were used as precursors


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instead (Supplementary Figure 7a). We expect that this methodology is likely to provide access to a wide range of TMMs, such as MoS, MoSe, and WTe when the metal sources are identified. Notably, XPS analyses of the residue attached to the CNT outer walls confirmed the formation of tellurium oxides, indicating that the oxygen in MoOx reacted with excessive tellurium in vapor form (Supplementary Figure 7b).

Conclusions In summary, we have developed a facile method for the isolation of MoTeNWs with welldefined atomic structures, by using CNTs as a template for self-assembly. The CNT-templated self-assembly gives rise to high-yield, bottom-up formation of isolated MoTeNWs. We further observed that a single MoTeNW inside a CNT exhibits complex structural dynamics, which has never been reported in bundled MoTeNWs. This observation suggests that single MoTeNWs themselves could possess unusual mechanical properties. Our nano-test-tube approach will give opportunities to explore the novel physics and chemistry of single-wired TMMs and cultivate the science of hybrid nanostructures. Experimental Procedures Sample Preparation: Self-assembly of MoTeNWs was independent of the MoTe2 crystal phases (2H/1T’) used as precursors. High-quality arc-discharge CNTs (Meijo Nano Carbon Co. Ltd.) were mainly employed as templates for the fabrication of the nanowires. Closed ends of CNTs were opened by an oxidation treatment, during which the temperature is increased to 500 °C in 6h in air. The as-prepared CNTs were degassed for 1h under a vacuum of 10–7 Torr. Typically, 0.2 mg of the open-ended CNTs was sealed in a straight quartz tube under vacuum (10–7 Torr)


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with 2 mg of partially oxidized MoTe2, and then heated at 550~1200 °C for 48h. After annealing, the tube was gradually cooled, the vacuum seal broken, and the sample prepared for TEM observation. In the experiments to investigate the CNT-diameter dependence of the nanowire formation, catalyst-supported chemical vapor deposition-grown CNTs and enhanced direct-injection pyrolytic synthesized CNTs (e-DIPS) were also employed as template. Opening the ends of eDIPS was carried out by heating at 560 °C for 20 min under air atmosphere. TEM Observation: A JEOL JEM-2100F high-resolution TEM was operated at an acceleration voltage of 80 kV under a pressure of 10–5 Pa. The obtained samples were sonicated in 15 mL dichloroethane for 30 minutes using an ultrasonic homogenizer (SONIFIER 450D, Branson Ultrasonics Co., Ltd), and 10 drops of the dispersion solution were deposited onto carbon-coated copper grids. Prior to the observations, the samples were heated at 200 °C under vacuum (10–6 Pa) for 30 minutes to eliminate impurities. TEM images were recorded on a Gatan MSC 794 1k×1k CCD camera with a typical exposure time of 0.3 s. Cs-corrected TEM observation: Cs-corrected TEM images were taken by using a JEMARM200F ACCELARM (cold FEG) equipped with a CEOS Cs corrector (CETCOR system) operated at 120 kV. OneView camera (4k×4k) was used for digital recording the images with an exposure time of 2.0 s. STEM and EELS Observations: HAADF images were taken at room temperature using a JEMARM200F ACCELARM (cold FEG) equipped with a CEOS ASCOR corrector, operated at 120 kV. The scan rate was 38 microseconds (38 µs) per pixel. STEM-EELS observations were acquired using a JEOL ARM-200F-based Ultra-high vacuum microscope equipped with a dodecapole Delta corrector and a cold field emission gun, operated


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at 60 kV. The convergence semi-angle was 37 mrad and the inner acquisition semi-angle was 55 mrad. The EELS core loss spectra were taken by using a Gatan low-voltage quantum spectrometer. XPS Spectroscopy: XPS analyses were carried out with an ESCALAB 250Xi (Thermo Fisher Scientific Inc.) by using monochromatic Al X-ray source. Instrument-base pressure was 7×10–10 Torr. High-resolution spectra were collected using an analysis 650 µm in diameter and 50 eV pass energy. Charge neutralization system was used for all analyses by flood gun with Ar gas. Raman Spectroscopy: Raman scattering measurement was conducted with the invia confocal Raman systems equipped with a microscope (Renishaw inVia). The laser spot size was φ2 µm and the laser power was 347 µW. The excitation wavelength was 633 nm (He-Ne Laser). DFT Simulation: DFT calculations for structural optimization and phonon eigenmode were performed using the VASP code under the generalized gradient approximation (GGA) for the exchange-correlation potential, with projector-augmented-wave (PAW) pseudopotentials.41–43 The parameterization of Perdew-Burke-Ernzerhof (PBE) was used for GGA. In the optimization, 1110 Monkhorst-Pack mesh was used to sample electronic states in the first Brillouion zone, and 800 eV energy cutoff was used for the plane-wave expansion. The optimized long-axis lattice constant of MoTeNW is 4.57 Å, and the maximum force on each atom in optimized structure was less than 0.001 eV/Å. As for phonon calculations, we obtained phonon eigenmodes by using the phonopy software,44 and used a supercell of 116 unit cell. Based on the sensitivity analysis of phonon frequency to supercell size, this supercell size (116) leads to a convergence of zone-center frequency to sufficient extent.


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FIGURES


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Figure 1. Schematic of synthesis and structure of MoTeNWs produced inside CNTs. (a) Schematic of the nano-test-tube reaction; (inset) actual image of a vacuum-sealed quartz tube. (b) Experimental and simulated (inset) HAADF-STEM images of an individual MoTeNW encapsulated inside CNTs. Scale bar, 1 nm. (c) Atomic structural model of the nanowire. (d) HAADF image of a single MoTeNW@CNT with the EELS chemical map of the Mo (red) and Te (green) M-edges in the area marked by the orange rectangle. Scale bar, 2 nm. (e, f) Lowermagnification HAADF-STEM images of MoTeNW@CNTs. Scale bar, 5 nm (left) and 100 nm (right), respectively.


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Figure 2. Spectroscopic characterization of MoTeNW@CNTs. (a) XPS Te-3d core-levels spectra of MoTeNWs inside CNTs (red) and in bulk (blue). (b) XPS C-1s core-levels spectra of pristine CNTs (red) and MoTeNW@CNTs (black) (c) Raman spectra of pristine CNTs (top) and MoTeNW@CNTs (bottom). (d) Schematic pictures showing the atomic vibrations for the calculated modes at 255 cm–1.


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Figure 3. Torsional motions of MoTeNWs confined by CNTs. (a) Schematic of dynamic movements of the nanowire. α is the out-of-plane twisting angle of the nanowire. (b) Experimental HAADF-STEM image of a bent and twisted MoTeNW confined within a single CNT. Scale bar, 1 nm. (c) Simulated HAADF-STEM images and the corresponding models of an individual MoTeNW encapsulated inside a CNT with different twisting angles.


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Figure 4. A possible mechanism for the growth of MoTeNWs inside CNTs. (a) Diameter distribution of the encapsulating (blue) and empty CNTs (gray). A space-filling model using (10, 10)CNT as an example shows that the diameters circa 1.3 nm allow for the self-assembly of perfectly-fitted MoTeNWs (inset). (b) XPS Te-3d5/2 core-levels spectra of the samples obtained at various annealing-temperatures. Contribution from MoTeNWs, TeNWs, and unintentionally contaminated TeO2, which are shown by red, green, and blue curves, respectively, are modeled by the Gauss function. (c) Possible pathway for the formation of MoTeNWs from bulk MoTe2 via MoOx. (d) XPS Mo-3d core-levels spectrum, and (e) Raman spectrum of partially oxidized


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MoTe2 precursors. Peaks labeled * indicate Ag, B1g (158 cm–1) and B2g, B3g (285 cm–1) modes of MoO3, respectively.

ASSOCIATED CONTENT Supporting Information. The following files are available free of charge via the Internet at https://pubs.acs.org. Statistical analyses of MoTeNW geometries; Cs-corrected TEM observation; Supporting data for XPS analysis; Further TEM information; results of other TMD precursors; details of growth mechanism (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Y. Nakanishi), [email protected] (Z. Liu), [email protected] (H. Shinohara) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally. Y.N. and H.S. designed all the experiments. M.N., S.S., and Y.N. synthesized the materials and carried out a part of the characterization. Z.L., Y.-C. L., and K.S. performed the microscopy experiments. T.S. performed the theoretical simulations. Y.N., T.K., and H.K. carried out Raman experiments. T.I., M.N., and Y.N. conducted XPS experiments and analysis. M.N., N.K., S.O., Y.S., and Y.N. discussed the growth mechanism.


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Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the financial support by Grant-in-Aids for Scientific Research S (No. 16H06350 to H.S. and 16H06333 to K.S.), Research Activity Start-up (17H06735 to Y.N.), and Young Scientists (18K14088 to Y.N.). Y.N. and K.S. acknowledge the NU−AIST alliance project. We thank Kimitaka Higuchi (Nagoya University) for technical assistance. This research project was also conducted as part of the 2017 Nakatani RIES Fellowship for S.S. with support from the Nakatani Foundation. This study was partially supported by the JST program “Nagoya University MIRAI Global Science Campus”. REFERENCES (1) Manzeli, S.; Ovchinnikov, D.; Pasquier, D.; Yazyev, O. V.; Kis, A. Nat. Rev. Mater. 2017, 2 (8), 17033–15. (2) Ajayan, P. M.; Kim, P.; Banerjee, K. Phys. Today 2016, 69 (9), 38–44. (3) Potel, M.; Chevrel, R.; Sergent, M.; Armici, J. C.; Decroux, M.; Fischer, Ø. J. Sol. St. Chem. 1980, 35 (2), 286–290. (4) Simon, A. Angew. Chem. Int. Ed. 1988, 27, 159–183. (5) Abo-Shaeer, J. R.; Raman, C.; Vogels, J. M.; Ketterle, W. Science 2001, 292 (5516), 476– 479. (6) Nicolosi, V.; Vrbanic, D.; Mrzel, A.; McCauley, J.; O’Flaherty, S.; Mihailovic, D.; Blau, W. J.; Coleman, J. N. Chemical Physics Letters 2005, 401 (1-3), 13–18.


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Page 24 of 26

(7) Nicolosi, V.; Vrbanic, D.; Mrzel, A.; McCauley, J.; O’Flaherty, S.; McGuinness, C.; Compagnini, G.; Mihailovic, D.; Blau, W. J.; Coleman, J. N. J. Phys. Chem. B 2005, 109, 7124–7133. (8) Bercic, B.; Pirnat, U.; Kusar, P.; Dvorsek, D.; Mihailovic, D. Appl. Phys. Lett. 2006, 88, 173103. (9) Yang, T.; Okano, S.; Berber, S.; Tománek, D. Phys. Rev. Lett. 2006, 96 (12), 125502– 125504. (10) Venkataraman, L.; Lieber, C. M. Phys. Rev. Lett. 1999, 83 (25), 5334–5337. (11)

Kibsgaard, J.; Tuxen, A.; Levisen, M.; Lægsgaard, E.; Gemming, S.; Seifert, G.; Lauritsen, J. V.; Besenbacher, F. Nano Lett. 2008, 8 (11), 3928–3931.

(12) Le, D.; Sun, D.; Lu, W.; Aminpour, M.; Wang, C.; Ma, Q.; Rahman, T. S.; Bartels, L. Surf. Sci. 2013, 611, 1–4. (13) Lin, J.; Cretu, O.; Zhou, W.; Suenaga, K.; Prasai, D.; Bolotin, K. I.; Cuong, N. T.; Otani, M.; Okada, S.; Lupini, A. R.; Idrobo, J.-C.; Caudel, D.; Burger, A.; Ghimire, N. J.; Yan, J.; Mandrus, D. G.; Pennycook, S. J.; Pantelides, S. T. Nature Nanotechnol. 2014, 1–7. (14) Zhu, H.; Wang, Q.; Cheng, L.; Addou, R.; Kim, J.; Kim, M. J.; Wallace, R. M. ACS Nano 2017, 11 (11), 11005–11014. (15) Zhu, H.; Wang, Q.; Zhang, C.; Addou, R.; Cho, K.; Wallace, R. M.; Kim, M. J. Adv. Mater. 2017, 29 (18), 1606264–1606265. (16) Yu, Y.; Wang, G.; Tan, Y.; Wu, N.; Zhang, X.-A.; Qin, S. Nano Lett. 2018, 18 (2), 675–681. (17) Popov, I.; Yang, T.; Berber, S.; Seifert, G.; Tománek, D. Phys. Rev. Lett. 2007, 99 (8), 085503–085504. (18) Ajayan, P. M.; lijima, S. Nature 1993, 361, 333–334.


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(19) Pagona, G.; Rotas, G.; Khlobystov, A. N.; Chamberlain, T. W.; Porfyrakis, K.; Tagmatarchis, N. J. Am. Chem. Soc. 2008, 130 (19), 6062–6063. (20) Sloan, J. & Monthioux, M. Filled Carbon Nanotubes (X@CNTS). In Carbon MetaNanotubes: Synthesis, Properties and Applications (eds. Monthioux, M.) 1st Edition, 225271 (John Wiley & Sons, Ltd, 2012). (21) Philp, E.; Sloan, J.; Kirkland, A. I.; Meyer, R. R.; Friedrichs, S.; Hutchison, J. L.; Green, M. L. H. Nature Mater. 2003, 2 (12), 788–791. (22) Talyzin, A. V.; Anoshkin, I. V.; Krasheninnikov, A. V.; Nieminen, R. M.; Nasibulin, A. G.; Jiang, H.; Kauppinen, E. I. Nano Lett. 2011, 11 (10), 4352–4356. (23) Shi, L.; Rohringer, P.; Suenaga, K.; Niimi, Y.; Kotakoski, J.; Meyer, J. C.; Peterlik, H.; Wanko, M.; Cahangirov, S.; Rubio, A.; Lapin, Z. J.; Novotny, L.; Ayala, P.; Pichler, T. Nature Mater. 2016, 15 (6), 634–639. (24) Dresselhaus, M. S.; Dresselhaus, G.; Saito, R. Jorio, A. Phys. Rep. 2005, 409, 47–99. (25) Ruppert, C.; Aslan, O. B.; Heinz, T. F. Nano Lett. 2014, 14, 6231–6236. (26) Spencer, J. H.; Nesbitt, J. M.; Trewhitt, H.; Kashtiban, R. J.; Bell, G.; Ivanov, V. G.; Faulques, E.; Sloan, J.; Smith, D. C. ACS Nano 2014, 8 (9), 9044–9052. (27) Koh, A. L.; Wang, S.; Ataca, C.; Grossman, J. C.; Sinclair, R.; Warner, J. H. Nano Lett. 2016, 16 (2), 1210–1217. (28) Lin, J.; Zhang, Y.; Zhou, W.; Pantelides, S. T. ACS Nano 2016, 10 (2), 2782–2790. (29) Hoffmann, R.; Shaik, S.; Scott, J. C.; Whangbo, M.-H.; Foshee, M. J. J. Sol. St. Chem. 1980, 34 (2), 263–269. (30) Pham, T.; Oh, S.; Stetz, P.; Onishi, S.; Kisielowski, C.; Cohen, M. L.; Zettl, A. Science 2018, 361 (6399), 263–266.


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Page 26 of 26

(31) Nakanishi, Y.; Omachi, H.; Fokina, N. A.; Schreiner, P. R.; Kitaura, R.; Dahl, J. E. P.; Carlson, R. M. K.; Shinohara, H. Angew. Chem. Int. Ed. 2015, 54, 10802–10806. (32) Fujihara, M.; Miyata, Y.; Kitaura, R.; Nishimura, Y.; Camacho, C.; Irle, S.; Iizumi, Y.; Okazaki, T.; Shinohara, H. J. Phys. Chem. C 2012, 116 (28), 15141–15145. (33) Liu, Z.; Joung, S.-K.; Okazaki, T.; Suenaga, K.; Hagiwara, Y.; Ohsuna, T.; Kuroda, K.; Iijima, S. ACS Nano 2009, 3 (5), 1160–1166. (34) Brainard, W. A. The Thermal Stability and Friction of the Disulfides, Diselenides, and Ditellurides of Molybdenum and Tungsten in Vacuum (10–9 to 10–6 Torr). NASA Technical Note TN D-5141; NASA: Washington, DC, 1968: pp. 1–26. (35) O'Hare, P. A. G.; Tasker, I. R.; Tarascon, J. M. J. Chem. Thermodyn. 1987, 19 (1), 61–68. (36) O'Hare, P. A. G.; Hope, G. A. J. Chem. Thermodyn. 1992, 24 (6), 639–647. (37) Srivastava, S. K.; Avasthi, B. N. J. Mater. Sci. 1985, 20 (11), 3801–3815. (38) Ueno, K.; Fukushima, K. Appl. Phys. Express 2015, 8, 095201–5. (39) Jaegermann, W.; Schmeisser, D. Surf. Sci. 1986, 165 (1), 143–160. (40) Saburi, T.; Murata, H.; Suzuki, T.; Fujii, Y.; Kikuchi, K. J. Plasma Fusion Res. 2002, 78 (1), 3–4. (41) Kresse, G.; Hafner, J. Phys. Rev. B 1993, 47, 558. (42) Kresse, G.; Furthmüller, J. Comp. Mater. Sci. 1996, 6, 15–50. (43) Kresse, G.; Furthmüller, J. Phys. Rev. B 1996, 54, 11169–11186. (44) Togo, A.; Tanaka, I. Scripta Mater. 2015, 108 (C), 1–5.


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Isolation of Single-Wired Transition-Metal Monochalcogenides by

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