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Chemical vapor deposition synthesis of near-zigzag single-walled carbon nanotubes with stable tube-catalyst interface

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Science Advances  13 May 2016:
Vol. 2, no. 5, e1501729
DOI: 10.1126/sciadv.1501729
  • Fig. 1 Schematic illustration and basic characterization of TPCVD method.

    (A) Schematic illustration of the TPCVD method. The temperature perturbation was realized by repeatedly changing the sample position in the furnace. This method used the interfacial formation energy between catalyst and SWNT, which was related to the helix angle of SWNTs in our system. (B) Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (inset) characterization of as-grown SWNT arrays from the TPCVD method. The tubes were transferred onto Si3N4 grids for TEM observation. (C) G-band Raman mapping of as-grown SWNT arrays after transfer onto a SiOx/Si substrate. The excitation laser frequency was 514 nm.

  • Fig. 2 Results and analysis of TPCVD methods.

    (A) Distribution of helix angle after a 90-cycle TPCVD process, which showed 72% content of SWNTs with small helix angle (<10°). Inset is the typical Raman spectra in a 50-μm line mapping. Radial breathing mode (RBM) peaks around 193 cm−1 are significantly enriched. (B) Chirality distribution of as-grown SWNT arrays analyzed by Raman spectroscopy. Hexagons in green refer to the chirality, which were resonant at 514 nm. More than 800 RBM signals were collected. (C) Density functional theory (DFT) calculation of the interfacial formation energy between SWNT and Fe, Co, and Ni catalysts. Small helix angle tubes (<10°) showed a lower interfacial energy among these three systems. (D) Models and diameter distributions of the simulation. Fe55 was used as a catalyst, and the diameter of SWNTs was confined to about 0.8 nm to match the catalyst.

  • Fig. 3 Dynamic analysis of TPCVD and the classification of SWNT structures.

    (A to D) SEM image of SWNT arrays with different times of temperature perturbation, representing 0, 30, 60, and 90 cycles, respectively. The decreasing length of SWNT might be caused by the catalyst inactivation. Scale bars, 50 μm. (E) Raman analysis of different RBM distributions. Bars in green, orange, purple, and blue refer to samples after 0, 30, 60, and 90 temperature perturbation cycles, respectively. The significant enrichment process was investigated. SWNT arrays after transfer onto a SiOx/Si substrate. The excitation laser frequency was 514 nm. More than 500 RBM signals were collected for each sample. (F to H) Three types of SWNT structures, representing types A, B, and C, separately. Type A structures were those that decrease with the number of perturbation cycles. Type B showed an increasing trend when perturbation cycles increased at first and then a decrease when perturbation cycles increased further. Type C increased continuously.

  • Fig. 4 Statistics and theoretical analysis of intratube junction.

    (A) G-band Raman mapping of an individual SWNT (inset) and the RBM peaks along the tube. An intramolecular junction was evident. The lowest position (shown in red) was closer to the catalyst stripe and was grown later in the TPCVD method. a.u., arbitrary unit. (B) Statistics of intratube junctions. In total, 50 junctions were analyzed, and the routes of A to B and B to C were found most frequently. (C) Formation energy of intratube junctions with different angle differences. The junctions with small (<5°) and large (>25°) angle differences had lower formation energy. Insets showed geometric structures of intratube junctions with different angle differences. (D) Schematic illustration of the TPCVD process.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/5/e1501729/DC1

    fig. S1. Temperature distribution in CVD furnace and schematic illustration of the TPCVD system.

    fig. S2. Raman spectroscope and chirality indication of as-grown SWNTs using TPCVD method.

    fig. S3. Chirality distribution excited by multiwavelength laser.

    fig. S4. Comparison of different methods to calculate the chirality distribution.

    fig. S5. Interfacial formation energy with metal catalysts.

    fig. S6. Geometry of intratube junctions with different initial and final structure.

    table S1. Chiralities and RBM shifts for indicating.

    table S2. Calculation of the IFE of SWNT on Fe55.

    table S3. Calculation of the IFE of SWNT on Co55.

    table S4. Calculation of the IFE of SWNT on Ni55.

    table S5. Calculation of formation energy of the intratube junction.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Temperature distribution in CVD furnace and schematic illustration of the TPCVD system.
    • fig. S2. Raman spectroscope and chirality indication of as-grown SWNTs using TPCVD method.
    • fig. S3. Chirality distribution excited by multiwavelength laser.
    • fig. S4. Comparison of different methods to calculate the chirality distribution.
    • fig. S5. Interfacial formation energy with metal catalysts.
    • fig. S6. Geometry of intratube junctions with different initial and final structure.
    • table S1. Chiralities and RBM shifts for indicating.
    • table S2. Calculation of the IFE of SWNT on Fe55.
    • table S3. Calculation of the IFE of SWNT on Co55.
    • table S4. Calculation of the IFE of SWNT on Ni55.
    • table S5. Calculation of formation energy of the intratube junction.

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