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1 doi: /nature Methods and synthesis 1.1 Synthesis of mono-dispersed catalyst precursors on sapphire Typically, 0.088g (NH 4 ) 6 Mo 7 O 24 4H 2 O was dissolved into 100 ml deionized water under stirring at 90 for 2h. This solution was diluted 100 times using ethanol at a concentration of 0.05 mmol/l and stored as a stock solution for the following experiments to prepare the monodispersed catalysts. Other concentrations of ammonium molybdate were prepared used a similar procedure. Likewise, 0.05 mmol/l (NH 4 ) 6 W 7 O 24 6H 2 O (or Ti(C 4 H 9 O) 4 or Zn(CH 3 COO) 2 2H 2 O, or CrCl 3 6H 2 O) H 2 O/ethanol (v 1 /v 2 =1/99) solution were prepared as catalyst precursors. A-plane (11-20) sapphire substrates (single side polished, miscut angle<0.5, surface roughness<0.5 nm) were purchased from Hefei Kejing Materials Technology Co., China. These substrates were cleaned using ultrasonication in Milli-Q water, followed by acetone, ethanol, and Milli-Q water again for 10 min, respectively. After cleaning, the sapphire substrates were annealed at 1100 in air for 8 h. 5 µl catalyst precursors with different concentrations were dispersed onto the sapphire substrates using micro-pipettes. Then, the sapphire substrates underwent a second annealing process (at 1100 in air for 8 h) for the mono-dispersion of catalyst on the sapphire substrates. 1.2 Growth of (12, 6) and (8, 4) SWNT arrays with high density and abundance The CVD growth was performed under atmospheric pressure in a one-inch quartz tube. The sapphire substrates, 4*5 mm 2 with well-dispersed catalyst precursor were put into the tube and heated in air to different temperatures for the reduction step. After the system was purged with 300 standard cubic centimeters per minute (sccm) argon, a flow of hydrogen was introduced for reduction to get the uniform-sized catalysts and then heated up to the growth temperature (usually 850 ) in an argon atmosphere free of hydrogen. Usually, 450 for MoO 3 and 850 for WO 3 were adopted to reduce the precursors for the growth of (12, 6) and (8, 4) tubes, respectively. Afterwards, argon was introduced through an ethanol bubbler for the growth of SWNT arrays. The flow rate of argon was set at 100 sccm during the growth of SWNT arrays. The flow rate of hydrogen was tuned to get different C/H ratios. In the case of the hydrogen-free growth, the H 2 was turned off when the temperature was up to 850. After the argon flushed the chamber for 5 min, the carbon source (ethanol) was introduced. After growth for 15 min, the furnace was cooled to room temperature in an argon atmosphere. 1

2 Figure S1. G band of SWNTs grown from monodispersed Mo catalysts without hydrogen. The G-band was clearly seen and was associated with metallic nanotubes. The bright green curve represents the BWF fit of G - and the blue represents Lorentzian fit of G +. Figure S2. SEM images of individual (12, 6) nanotubes (a) and a (12, 6) SWNT array transfered to a SiO 2 (300 nm)/si substrate(c). The corresponding Raman spectrum of an individual SWNT and the Raman mapping spectra of SWNTs in the array are shown in (b) and (d), respectively. The dominant RBM peak was still at ~197 cm -1, in accordance with the value obtained on the sapphire substrate. 2

3 0.020 Optical Contrast Wavelength (nm) Figure S3. Optical reflection spectrum for the (12,6)SWNT arrays transferred to SiO 2 (90 nm)/si substrate. 2 Calculate the chirality purity of SWNTs based on Raman The as-grown SWNT array on a sapphire substrate was characterized using Raman spectroscopy with different excitation lasers (Horiba HR800 Raman system with 488 nm, 514 nm, 633 nm and 785 nm lasers). Raman line mappings in the same region were done to quantify the percentage of SWNTs with specific chirality in the arrays by counting the numbers of RBMs. Table S1. Specific RBM peaks (194~201 cm -1 ) from Raman spectra with 633 nm excitation were assigned as (12, 6). ω RBM (cm -1 ) 198.(5) 198.(5) 197.(6) 196.(3) 197.(6) 196.(3) 197.(6) 195.(2) 199.(8) 197.(6) 200.(1) 196.(3) 196.(3) 197.(6) 195.(0) 198.(5) 198.(8) 198.(8) 195.(0) 197.(6) 196.(3) 198.(3) 198.(5) 200.(1) 197.(6) 197.(6) 197.(6) 195.(0) 198.(8) 197.(6) 198.(8) 200.(1) 196.(3) 196.(3) 197.(6) 196.(3) 197.(6) 197.(6) 195.(0) 197.(6) 197.(6) 198.(8) 197.(6) 196.(3) 197.(6) 197.(6) 198.(8) 196.(3) 196.(3) 198.(8) 197.(6) 197.(6) 198.(8) 197.(6) 198.(8) 198.(8) 197.(6) 196.(3) 197.(6) 196.(3) 196.(3) 196.(3) 197.(6) 197.(6) 197.(6) 200.(1) 198.(8) 195.(0) 200.(1) 195.(0) 3

4 Table S2. Statistics on numbers of RBM peaks collected using 788, 633, 514 and 488 nm excitations for (12, 6) tubes sample. All Raman measurements were performed in the same area of the sample. Laser wavelength (nm) total Number of RBM peaks detected Number of (12, 6) RBM peaks % Table S3. Specific RBM peaks (280~285 cm -1 ) from Raman spectra with 633 nm excitations were assigned as (8, 4). ω RBM (cm -1 ) 281.(4) 283.(7) 282.(5) 281.(3) 283.(4) 283.(3) 284.(6) 283.(2) 284.(2) 283.(2) 281.(1) 282.(3) 284.(8) 284.(1) 283.(0) 285.(0) 283.(8) 283.(8) 283.(0) 285.(4) 285.(3) 282.(7) 283.(5) 280.(2) 282.(8) 281.(6) 280.(6) 284.(0) 283.(4) 282.(8) 281.(8) 283.(1) 285.(3) 283.(3) 281.(6) 284.(1) 284.(6) 283.(4) 283.(0) 284.(6) 284.(6) 280.(8) 280.(6) 283.(5) 284.(6) 284.(6) 283.(8) 282.(3) 281.(3) 283.(6) 284.(6) 285.(2) 282.(8) 284.(6) 282.(8) 280.(5) 284.(2) 283.(3) 282.(6) 280.(3) 285.(3) 281.(3) 283.(5) 280.(6) 281.(6) 283.(1) 280.(8) 283.(0) 283.(1) 284.(0) Table S4. Statistics on numbers of RBM peaks collected using 788, 633, 514 and 488 nm excitations for (8, 4) tubes sample. All Raman measurements were performed in the same area of the sample. Laser wavelength (nm) total Number of RBM peaks detected Number of (12, 6) RBM peaks % 3 Quantification of the purity of (12, 6) tubes using UV-Vis-NIR absorption spectroscopy The as-grown SWNTs were removed from the sapphire substrates and dispersed into aqueous solutions of sodium dodecyl sulfate (SDS) for UV-Vis-NIR measurements. SWNTs from 40 samples were collected. 4 The optical reflection spectrum measurement and corresponding chirality assignment 4

5 SWNT arrays grown on sapphire were transferred onto SiO 2 /Si substrates with 90 nm SiO 2 by applying the peel-off method. The detailed configuration of the optical setup and the method of measurement have been described elsewhere (ref. 41, 42). From the optical reflection spectrum, the transition energies at the optical resonance peaks were identified as 2.00 ev and 2.16 ev for (12, 6) nanotubes, similar to values reported in the literature (ref. 41, 42). Due to the dielectric screening effect from the substrate and the residuum of nanotube, several decade mev shift was permitted when assigning the nanotube chirality according to the atlas of carbon nanotube optical transitions. From these assignments we confirmed the nanotube arrays are (12, 6) enriched. A similar identification of (8, 4) tubes was done using optical reflection spectrum. The peak at about 2.20 ev deviated slightly from that in the literature (ref. 41), which may be caused by the dielectric screening effect from the substrate. Figure S4. (a) Optical reflection spectrum of the (8, 4)SWNT arrays. (b) Relative chirality distribution of the as-grown SWNT arrays analyzed by Raman measurements. 5 Fabrication and measurements of FET devices SWNT arrays grown from molybdenum and tungsten catalysts on sapphire were directly fabricated into top-gate transistors through a self-aligned U-gate process. Electron beam lithography (EBL) was used to fabricate the source and drain electrodes by depositing Ti/Pd (0.5/70 nm) and then 10 nm Pd as a self-aligned contact electrode. The electrical characteristics of these FET devices were measured in air with a semiconductor analyzer (Keithley 4200 SCS). Figure S5. (a) Typical transfer characteristic curve of FET devices fabricated on individual SWNT randomly chosen from the (12, 6)-enriched or (8, 4)-enriched samples. (b) Statistics of the FET devices according to the I on /I off ratios. 5

6 6 Other characterizations The as-grown SWNTs and catalysts on substrates were inspected with scanning electron microscopy (SEM, Hitachi S4800 field emission, Japan) and atomic force microscopy (AFM, VeecoNanoScopeIIIA, Veeco Co.) to characterize the morphology and structure. The fieldemission high-resolution transmission electron Microscope (HRTEM Philips Tecnai F20) measurements were performed for nanotube chirality assignment based on the electron diffraction patterns. XPS (ESCALab250, Thermo Scientific Corporation) was used to confirm the chemical composition and content of the catalysts on substrate surface. Hydrogen temperature programmed reduction (H 2 -TPR) was carried for investigating the surface chemical information between the molybdenum and aluminum oxide. 7 Analysis of the oxide monolayer dispersed on sapphire surface We can estimate the maximum monolayer capacity by using the so-called close-packed monolayer model. As shown in Fig. S6, the O 2- ions from MoO 3 form a close-packed layer on the surface of sapphire with the Mo 6+ ions located at the interstices formed by O 2- ions. By taking 1.4 Å for the radius of O 2- ions, the area of our substrate 4 6 mm 2, and Avogadro's constant we can calculate the maximum monolayer capacity of MoO 3 : Figure S6. Close-packed monolayer model for MoO 3 on sapphire surface. The O 2- ions from MoO 3 form a close-packed layer on the surface of sapphire and the Mo 6+ ions located at the interstices formed by O 2- ions. Sapphire substrates supported molybdenum oxide catalysts were prepared by dropping molybdate solution on them and annealing at We concluded that the molybdate decomposed to form molybdenum oxide on the substrate after annealing. This was confirmed by the XPS measurement (Fig. S7). After annealing at a temperature of 1100, no nanoparticles were found on the surface of sapphire, as shown by the AFM image in Fig.1c. We further increased the concentration of the molybdenum catalyst precursors from 0.05 mmol/l to 1.0 mmol/l and 20.0 mmol/l, followed by the same annealing process. Again, no nanoparticles were found on the substrate at all 6

7 concentrations (Fig. S8, a-c). X-ray photoelectron spectroscopy (XPS) analysis (Fig. S8, d-f) showed that the ratio of surface Mo/Al remained almost constant regardless of the considerable difference in the concentrations. This further confirmed that MoO 3 was monodispersed on sapphire. Figure S7. XPS analysis of the substrate with molybdenum precursors before (a) and after annealing (b). Figure S8. Characterization of MoO 3 dispersed on sapphire substrate. (a-c): AFM images of the surface morphology of sapphire loaded with different concentrations of the molybdenum catalyst precursors after annealing. (d-f): the corresponding XPS measurements. 7

8 Figure S9. HRTEM Characterization shows the appearance of Mo 2 C nanoparticles on Al 2 O 3 support. 8 Analysis of kinetic control for chiral selectivity 8.1 Other catalysts for the kinetics growth of SWNTs with chiral angle 19.1 According to the literature, many other oxides, such as TiO 2, Cr 2 O 3 and ZnO, can also be monodispersed on the surface of sapphire after annealing. Thus, we used TiO 2, Cr 2 O 3 and ZnO as catalysts to grow SWNTs, and also obtained (12, 6) or (8, 4)-enriched SWNT arrays. 8.2 The effect of initial temperature for reduction Figure S10. Raman spectra of SWNTs catalyzed by nanoparticles reduced at different initial temperatures (a-b:450 ;c-d:650 ;e-f:850 ) with different excitation wavelengths. 8.3 The effect of C/H ratio 8

9 Figure S11. Raman spectra of SWNTs grown under different C/H ratios(a-c:c/h ratio=100:0; d-f:c/h ratio=100:50; g-i:c/h ratio=100:200) with different excitation wavelengths, 514 nm(a, d and g), 633 nm(b, e and h) and 785 nm(c, f and i), respectively. The C/H ratio was defined according to the flow rate of argon (through an ethanol bubbler). 8.4 The (12, 6) tubes in other catalysts Figure S12. Raman spectra of SWNTs grownusing different catalysts (a-b:tio 2 ; c-d:cr 2 O 3 ; e- f:zno) with different excitation wavelengths. 9

10 8.5 The appearance of (10, 5) tubes Figure S13. Raman spectra showing the appearance of (10, 5) SWNTs (RBM at ~230cm -1 ) using 785 nm excitation laser. 8.6 The selectivity is free of substrates Figure S14. (a) SEM image of SWNTs grown on the edge of the sapphire substrate, who owns different plane with the center of the substrate.the randomly oriented SWNTs are highlighted by the red circle. (b) Raman spectra of the as-grown SWNTs in the red circle of (a) showed the enrichment of (12, 6) SWNTs. (c) SEM image of the SWNTs grown on electron-beam deposited alumina. (d) The corresponding Raman spectra of the SWNTs in (c), also indicating the enrichment of (12, 6) SWNTs. 8.7 The effect of the plane of the substrate In addition, we found that the MoO 3 monolayer dispersed onto the sapphire surface was 10

11 independent of the crystal plane of the sapphire substrate. Randomly oriented SWNTs grown on the edge of the sapphire substrate or on electron-beam deposited alumina were also detected through Raman measurements and assigned to (12, 6). Figure S15. SEM (a) and Raman (b) characterizations of SWNTs dispersed in SDS aqueous solution for optical absorption measurements. RBM peaks were also found at ~197 cm -1, corresponding to (12, 6) SWNTs. Table S5. Partial statistics on lengths of the tubes detected in Fig. 2g. (n, m) Length (μm) (n, m) Length (μm) (12, 6) (15, 14) 43.1 (18, 11) 35.1 (15, 11) 36.8 (12, 6) (15, 3) 18.4 (15, 5) 13.5 (12, 6) (18, 6) 18.9 (13, 12) 40.7 (17, 5) 60.7 (11,8) 45.1 (12, 6) (16, 11) 51.6 (18, 8) 80.6 (8, 8) 56.7 (22, 2) 17.3 (15, 14) 43.2 (21, 4) 20.4 (13, 7) 75.6 Table S6. Statistics of selectivity for different samples No Total tubes (12, 6) tubes Selectivity 88% 84% 92% 88% 90% 11

12 9 Computational details All the calculations were performed within the framework of density functional theory (DFT) implemented in the Vienna Ab initio Simulation Package 51,52 (VASP). Generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof 53 (PBE) parametrization was chosen to describe the electronic exchange and correlation items. The interaction between valence electrons and ion cores was included in the projected augmented wave 54,55 (PAW) method with the cutoff energy set as 400 ev. In order to modify the contributions of the van der Waals interaction and spin polarization, the Grimme DFT-D2 method 56 and the spin-polarized calculations were both considered. Integration over the Brillouin zone was performed using the Monkhorst Pack method 57. Special 2*2*1 k-points uniformly sampled in the Brillouin zone were used to ensure an energy convergence of less than 0.1 mev/atom. All the structures were optimized within the recommended conjugate gradient algorithm until the maximum force component on each atom converged to less than 0.01 ev/å. Figure S16. The computational model of calculating the formation energy of SWNT on catalyst surface. (a) the edge formation energy of SWNT. (b) the binding energy between SWNT and the catalyst surface. A certain section of SWNT for special chirality (SWNT-1), of which the edges are terminated with hydrogen atoms, was divided equally into two same parts (SWNT-2). For each part, one end is passivated with hydrogen atoms, another is exposed without passivation. Therefore, the edge energy of SWNT can be calculated in the coming formula: E E -E 2 f SWNT SWNT-2 SWNT-1 (1) In the slab model, the surface formation energy of the mono-element catalyst can be calculated as: E f surf Esurf nebulk S (2) 2 In which E surf and E bulk is the energy of the surface and primitive cell respectively. S is the area of the chosen surface. n can be defined as: n N N (3) surf bulk where N surf and N bulk is the total number of atoms in the surface and the primitive cell, respectively. 12

13 However, because the catalysts we chose consist of bi-elements (WC or Mo 2 C), there would be two kind of surface formation energy corresponding to the metal and the carbon, respectively. As all the SWNTs will be placed on the metal-exposed surface in our calculation model. Therefore, the formula of the surface formation energy can be modified: E = E n E N E 2S (4) f surf surf bulk comp C where n comp is the number of compensating carbon atoms to make the atomic ratio in the slab match that in the bulk. E C is the energy of per carbon in graphene, S is the surface area. n is defined as: n N N N (5) surf comp bulk When placing the SWNTs with different chiralities on the catalyst surface, the binding energy between SWNT and catalyst surface can be written as: E E -E E (6) b SWNT 2 surf SWNT 2 surf Then the formation energy of SWNT on catalyst surface can be defined as the combination of the edge energy of SWNT and the binding energy between SWNT and the catalyst surface. After normalization, the formation energy can be rewritten as: E E E S E d (7) f f SWNT f surf int b where d is the diameter of the SWNT, S int is estimated as: S int dd (8) int d int is the interaction distance between carbon atom and tungsten atom on the interface and is approximated as 3.40 Å. In the case of (8, 4) SWNT enrichment on the tungsten carbide (WC) catalyst, based on the XRD information and the structure match between the SWNT and WC surface, the quasifourfold symmetry WC (1 0 0) plane is chosen to match the SWNTs. A six atomic layer is used with the bottom tungsten and carbon layer fixed to simulate the bulk. In order to illuminate the symmetry-dominant chirality selectivity, we chose three groups of SWNT, namely zz-type (n, 0) (n=7, 8, 9, 10, 11, 12, 13), ac-type (n, n) (n=3, 4, 5, 6), and a set of SWNTs with similar diameters, including (11, 0), (10, 1), (9, 3), (8, 4), (7, 5), (6, 5), (6, 6). In the SWNT-WC system, a supercell with a volume of Å 3 is adopted and periodic boundary condition is considered. Vacuum layer is higher than Å to avoid the images interferences. Figure S17. The high-symmetry relative position of SWNT on WC (1 0 0) surface. (a) square (b) diamond (c) rectangle. The three relative positions are labelled in red dotted line. The 13

14 tungsten and carbon atoms are colored blue and grey. The top layer consisting of tungsten atoms is highlighted in green. When choosing the initial structure of SWNTs on the WC (1 0 0) surface (shown in Figure S17), there are three different high-symmetry relative positions from the vertical view, which are marked as square (S), diamond (D), and rectangle (R). Therefore, such three initial structures are all selected throughout our calculations. The lowest formation energy will be taken as zero point formation energy reference (In our calculations, the formation energies of (3,3) SWNT in lowest series are the lowest and taken as the zero point). The formation energy of SWNT on WC (1 0 0) surface are shown in Figure S18. All the data presented are corresponding to the lowest formation energy considering the three high symmetry positions. Among the chiralities we chose, (8, 0) and (12, 0) SWNTs are both of four-fold symmetry which is consistent with the symmetry of WC (1 0 0) surface. From the perspective of deformation (shown in Figure S19), the (8, 0) and (12, 0) SWNTs can keep their symmetry structures after binding on the WC (1 0 0) surface with minor deformations compared with other zz-swnts, which implies the better symmetry match between the SWNT and the catalyst. Figure S18a displays the lowest formation energy of zz-swnts on WC (1 0 0) surface. The lowest formation energies of (8, 0) and (12, 0) are 0.18 and 0.27 ev/nm respectively, which are much lower than those of other non-four-fold symmetry zz-swnts (All are above 2.00 ev/nm), which implies the symmetry match between SWNT and the catalyst structure should play an important role in the SWNT chirality selectivity. Also from the most stable structures of zz- SWNTs on WC (1 0 0) (shown in Figure S19), it can be deduced that in the most stable structures, more edge C atoms of (8, 0) and (12, 0) are inclined to stay at the high-coordination sites like bridge, and hollow, which could increase the binding strength of SWNT on the WC (1 0 0) surface and reduce the formation energy. As displayed in Figure S19b, even some 4- coordination sites of edge C atoms emerge, which is consistent with the extremely low formation energy of (8, 0) SWNT. Figure S18. The lowest formation energies of SWNTs with different chiralities on WC (1 0 0) surface. (a), zz-swnts (b), ac-swnts (c), SWNTs with similar diameters. The overall tendency for ac-swnts can also prove the symmetry-control of SWNT chirality. As is shown in Figure S20b, the lowest formation energy of (4, 4) SWNT which has a four-fold rotation axis is 0.69 ev/nm and is much lower than those of (5, 5) (1.47 ev/nm) and (6, 6) (1.98 ev/nm). However, (3, 3) SWNT, which possesses a three-fold rotation axis and does not match 14

15 the symmetry of the WC (1 0 0) surface (shown in Figure S20a), displays a much lower formation energy than that of (4, 4) SWNT. Such results seemingly adverse to the symmetry theory result from the diameter effect. In the case of (3, 3) SWNT, all the edge atoms can insert into the high-symmetry sites with little steric effect. While for the (4, 4) SWNT, few C atoms could stay at the high-symmetry sites due to a stronger steric effect. Therefore, the diameter match between the SWNT and the catalyst structure is also of great significance and can supplement the symmetry-controlled chirality-selectivity growth of SWNTs. Figure S19. The most stable optimized structure of zz-swnts on WC (1 0 0) surface. Figure S20. The most stable optimized structure of ac-swnts on WC (1 0 0) surface. In order to explain the high chirality selectivity of (8, 4) SWNT, we chose a group of SWNTs with similar diameters. As speculated, (8, 4) SWNT has a four-fold rotation axis and could match the symmetry structure of WC (1 0 0) surface (shown in Figure S21d). It can be apparently seen (Figure S18c) that the formation energy of (8, 4) SWNT is 1.56 ev/nm and is much lower than 15

16 those of other chosen SWNTs, which implies a higher chirality selectivity towards (8, 4) SWNT and proves our aforementioned symmetry model. Figure S21. The most stable optimized structure of SWNTs with similar diameters on WC (100) surface. As there are three different relative positions between the SWNT and WC (1 0 0) surface (marked as S, D and R), the three lowest formation energy based on the relative positions are extracted and an average formation energy could be obtained. Figure S22 shows the average formation of SWNTs mentioned above on WC (1 0 0) surface (The detailed data for the three relative positions are shown in Figure S23). Although all the average formation energies of the chosen SWNTS are much higher than the lowest ones, the tendency of the average formation energies for the three groups of SWNTs are totally the same as that of the lowest formation energies, which verifies our symmetry match theory. Figure S22. The average formation energy of SWNTs with different chiralities on WC (1 0 0) surface. (a), zz-swnts (b), ac-swnts (c), SWNTs with similar diameters. 16

17 Figure S23. The formation energies of SWNT on WC (1 0 0) surface with different relative positions. For (9, 0) and (13, 0) SWNT, the rectangle and square relative structure are not stable respectively and the formation energies for these two structures are not given. Finally, we estimated the theoretical percentage of SWNTs with similar diameters. Both the nucleation density N and the growth rate R are considered in our calculation models. The nucleation density N depends on the thermodynamic factor and can be estimated as: G / k E f / k BT BT N e e (9) Where E f is the formation energy of SWNTs with certain chiralities. k B is the Boltzmann constant, T is the experimental temperature and taken as 1123 K. Therefore, the estimated quantities of the SWNTs of chiralities P can be estimated as: (10) Where E fi is the formation energy of SWNT normalized with nm. d is the diameter of the SWNT, As the slight diameter difference between these SWNTs also cause a problem in population comparison. we used the diameter of (8,4) for all of them in order to make a fare comparison. The estimated percentage of SWNTs with similar diameters will be shown in Figure S24 (the data are listed in table S7). Figure S24. The estimated quantities of SWNTs with similar diameters by theory. 17

18 Table S7 The estimated quantities of SWNTs with similar diameters by theory Chirality (11,0) (10,1) (9,3) (8,4) (7,5) (6,5) (6,6) E f (ev/nm) E f (ev/cnt) Population (T = 1123 K) 1.4* * * * * *10-6 Supplementary References 31. Chiang, W.H. & Mohan Sankaran, R. Linking catalyst composition to chirality distributions of as-grown single-walled carbon nanotubes by tuning Ni x Fe 1-x nanoparticles. Nat. Mater. 8, (2009). 32. Fouquet, M. et al. Effect of Catalyst Pretreatment on Chirality-Selective Growth of Single- Walled Carbon Nanotubes. J. Phys. Chem. C 118, (2014). 33. Yang, F. et al. Growing Zigzag (16, 0) Carbon Nanotubes with Structure-Defined Catalysts. J. Am. Chem. Soc. 137, (2015). 34. Yuan, Q. & Ding, F. How a zigzag carbon nanotube grows. Angew. Chem. 54, (2015). 35. Fantini, C. et al. Optical transition energies for carbon nanotubes from resonant Raman spectroscopy: environment and temperature effects. Phys. Rev. Lett. 93, (2004). 36. Steiner, M. et al. How does the substrate affect the Raman and excited state spectra of a carbon nanotube? Appl. Phys. A 96, (2009). 37. Zhang, Y. et al. Raman Spectra Variation of Partially Suspended Individual Single-Walled Carbon Nanotubes. J. Phys. Chem. C 111, (2007). 38. Huang, L. et al. A Generalized Method for Evaluating the Metallic-to-Semiconducting Ratio of Separated Single-Walled Carbon Nanotubes by UV vis NIR Characterization. J. Phys. Chem. C 114, (2010). 39. Miyata, Y., Yanagi, K., Maniwa, Y. & Kataura, H. Optical Evaluation of the Metal-to- Semiconductor Ratio of Single-Wall Carbon Nanotubes. J. Phys. Chem. C 112, (2008). 40. Nair, N., Usrey, M. L., Kim, W.-J., Braatz, R. D. & Strano, M. S. Estimation of the (n,m) Concentration Distribution of Single-Walled Carbon Nanotubes from Photoabsorption Spectra. Anal. Chem. 78, (2006). 41. Liu, K. et al. An atlas of carbon nanotube optical transitions. Nat. Nanotechnol. 7, (2012). 42. Liu, K. et al. High-throughput optical imaging and spectroscopy of individual carbon nanotubes in devices. Nat. Nanotechnol. 8, (2013). 43. Ding, L. et al. Self-Aligned U-Gate Carbon Nanotube Field-Effect Transistor with Extremely Small Parasitic Capacitance and Drain-Induced Barrier Lowering. ACS Nano 5, (2011). 18

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