Temperature Dependence of Catalyst-Free Chirality-Controlled Single

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Temperature Dependence of Catalyst-Free Chirality-Controlled Single-Walled Carbon Nanotube Growth from Organic Templates Hai-Bei Li, Alister James Page, Stephan Irle, and Keiji Morokuma J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/jz4015647 • Publication Date (Web): 04 Sep 2013 Downloaded from http://pubs.acs.org on September 5, 2013

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The Journal of Physical Chemistry Letters

Temperature Dependence of Catalyst-Free Chirality-Controlled Single-Walled Carbon Nanotube Growth from Organic Templates Hai-Bei Li,1 Alister J. Page,2 Stephan Irle,3* and Keiji Morokuma1* 1 2

Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, Japan

Discipline of Chemistry, School of Environmental and Life Sciences, The University of Newcastle, Callaghan 2308, Australia

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WPI-Institute of Transformative Bio-Molecules and Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

*

To

whom

all

correspondence

should

be

addressed.

Email:

[email protected];

[email protected]

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Abstract Temperature dependence of catalyst-free single-walled carbon nanotube (SWCNT) growth from organic molecular precursors is investigated using DFTB quantum chemical molecular dynamics simulations and DFT calculations. Growth of (6,6)-SWCNTs from [6]cycloparaphenylene ([6]CPP) template molecules was simulated at 300, 500, and 800 K using acetylene (C2H2) and ethynyl radicals (C2H) as growth agents. The highest growth rates were observed with C2H at 500 K. Higher temperatures lead to increased defect formation in the SWCNT structure during growth. Such defects, which cause the loss of SWCNT chirality control, were driven by radical addition reactions with inherently low kinetic barriers. We therefore propose that lower temperature is optimal for the C2H radical mechanism of SWCNT growth, predict the existence of an optimum SWCNT growth temperature that balances the rates of growth and defect formation at a given C2H/C2H2 ratio.

TOC Graphic

Keywords: Carbon nanotube, chirality, control, organic template, cycloparaphenylene


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The electronic and optical properties of single-walled carbon nanotubes (SWCNTs) are determined chiefly by their (n,m) chirality. SWCNT-based devices that require precise control over these properties therefore require precise control over SWCNT chirality. For this reason, chirality-controlled synthesis remains the outstanding challenge in SWCNT growth research. Preeminent synthesis techniques, such as carbon-arc,1 laser evaporation,2 and catalytic chemical vapor deposition (CCVD),3 are incapable of such control, instead producing wide distributions of different (n,m) SWCNT chiralities. These distributions can be narrowed via careful control of experimental conditions.4 Alternatively, particular (n,m) chiralities can be enriched post-synthesis,5 however such an approach does not scale well to industrial production. A different approach, SWCNT ‘cloning’, has recently been reported,6 and enables templated regrowth of SWCNTs with specific chiralities. An alternative, ‘bottom-up’ approach for chirality-controlled SWCNT growth has been proposed as a potential solution to this problem, following the synthesis of [n]cycloparaphenylenes ([n]CPPs).7 These hoop-shaped carbon nanorings can be regarded as SWCNT ‘building blocks’ with fixed (n,m) chirality and diameter. It has been proposed that chirality-controlled SWCNT growth could be achieved by extending these templates using low temperature CVD. Itami et al. recently provided the first evidence that this may be possible, by demonstrating alcohol CVD of SWCNTs from [12]CPP.8 Scott and co-workers9 proposed that SWCNT growth in this manner is the result of Diels-Alder (DA) cycloadditions ad infinitum, with a dieneophile growth agent and a diene SWCNT. In the absence of a catalyst, however, this route is prohibited by barriers of up to 80 kcal mol-1, depending on the diameter of the template.10 On the other hand, we have earlier revealed the dual role of the ethynyl (C2H) radical in low-temperature templated SWCNT growth;10,11 it activates the CPP fragment by abstracting hydrogen atoms, and simultaneously acts as growth agent. The ethynyl radical is a result of C2H2 decomposition,12-14 and has been observed as predominant species under relevant, low temperature conditions.13 Notably, C2H was also implicated in the recent experimental SWCNT study of Itami et al.8 Chemical reaction barriers associated with radical-based SWCNT growth are smaller by at least an order of magnitude, compared to those for DA cycloaddition. Herein we investigate the role of temperature on chirality-controlled SWCNT growth from such organic templates. We take [6]CPP → (6,6)-SWCNT growth as a model system, and use DFTB (density functional tight binding) quantum chemical molecular dynamics (QM/MD) to simulate SWCNT growth. SWCNT growth was induced by C2H radical addition to the [6]CPP template at the temperatures of 300, 500, and 800 K. We additionally determine the reaction rate constants of the hexagon and pentagon (i.e. defect) formation via radical- and DA-based mechanisms of SWCNT growth using transition state theory (TST) and the density functional theory (DFT). The computational methodology employed here is the same to that used in our recent investigations,10,11 with 20 trajectories for each temperature being ACS Paragon Plus Environment

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calculated to ensure reliable statistics. Growth is induced by the addition of C2H radicals to randomly chosen sites on the CPP precursor at intervals of 10 ps. Full details of the QM/MD simulations are provided in Supporting Information. Figure 1 depicts the hexagon addition distributions for growth at 300, 500 and 800 K, respectively, following 245 ps. It is immediate from Figure 1 that SWCNT growth at 300 K, as measured by hexagon addition, is noticeably slower compared to that at 500 and 800 K. In 90% of 300 K trajectories between four and seven new hexagons were added. Conversely, hexagon addition distributions at 500 and 800 K shift noticeably towards higher hexagon populations: the number of trajectories with four new hexagons decreases sharply, while the number of trajectories with 8 ~ 10 new hexagons increases. On average, 5.8, and 6.8 and 6.7 hexagons are added during this period at 300, 500 and 800 K, respectively. These data are remarkably similar with previous simulations of Fe-catalyzed SWCNT growth.15 Interestingly, while the average growth rates at 500 and 800 K are essentially equal, hexagon addition distributions at these temperatures differ significantly, suggesting a difference in growth mechanism. At higher temperature, terminating polyyne chains and their supporting hexagonal rings exhibit larger vibrational and torsional motion. This on one hand could potentially promote ring formation; this is certainly what a comparison of hexagon addition distributions between 300 and 500 K suggests. On the other hand, large-amplitude torsional modes potentially promote instability in the SWCNT structure itself, which in turn results in irregular growth rates and more defect formation.

Figure 1. Hexagon addition distributions during growth at 300 K, 500 K, and 800 K, after 245 ps.


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The formation of defects during SWCNT growth is unavoidable due to the low barrier heights associated with their formation, especially the pentagon formation. We illustrate the different pathways of pentagon formation and their statistical weights in Figure 2. We note here that hexagon formation is overwhelmingly dominated by the reaction pathway depicted in Figure 3(a); we present other observed minor pathways in the Supporting Information (Figure S1). Conversely, there are a number of competitive mechanisms for pentagon formation. Of these, “induced pentagon” pathways are dominant. These pathways result in the almost simultaneous formation of multiple pentagons in the same region of the SWCNT, and consist of a number of different chemical routes. Induced pentagon pathways constitute more than 30% of all total defect formation. This implies that the initial introduction of defects into the SWCNT structure induces further defect formation, particularly at high temperature. The direct insertion of C2H into the dehydrogenated “bay region” (Pent. 1 in Figure 2) is another important source of pentagon formation.

Figure 2. Prominent pathways of defect pentagon formation observed in 120 trajectories at 300 K, 500 K, and 800 K.


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Figure 3. (a) B3LYP/6-31G(d) reactive potential energy surface for the predominant hexagon (Hex.1 in Figure S1) and pentagon addition (Pent.1 in Figure 2) to [6]CPP precursor via C2H insertion. Free energies are calculated at 300 K and atmospheric pressure. (b) Temperature dependence of reaction rate constants for hexagon (kI) and pentagon (kII) formation.

TST reaction rate constants for the predominant hexagon and pentagon addition pathways (Hex.1 and Pent.1, respectively) are presented in Figure 3(b). Reaction rates for pentagon defect formation exceed those for hexagon formation across the range of temperatures most pertinent to CVD SWCNT growth. The kinetic advantage that defect formation holds over hexagon formation is greatest at lower temperatures. While pentagon defect formation is kinetically more favorable than hexagon formation, the thermodynamic stability of the hexagon product is significantly greater than that of the pentagon defect. Hexagon and pentagon formation during SWCNT growth are therefore competitive processes, ACS Paragon Plus Environment

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and this is consistent with QM/MD simulations that show conversion of pentagons to hexagons (although not frequently). The reverse reaction, i.e. hexagon to pentagon conversion, is never observed. Reaction rate constants of hexagon and pentagon formation increase with increasing temperature, and this is consistent with QM/MD results that show faster growth at higher temperatures. Figure 4 shows ring formation statistics during growth at 300, 500 and 800 K. It is immediate from this figure that higher temperatures result in more pentagon defect formation during growth, and this is consistent with the reaction rates of pentagon and hexagon formation shown in Figure 3. There is a particularly noticeable difference between 300 and 500 K in this respect. It can be attributed to the fact that higher temperatures result in a greater extent of C2H-driven hydrogen abstraction from the growing SWCNT, which results in more radical sites on its edge. Higher temperatures simultaneously increase the vibrational and torsional motion of nearby terminating polyyne chains on the growing SWCNT. The combination of these two factors, and the relative kinetics of defect pentagon formation, discussed above, account for this temperature dependence. Interestingly, 80% of trajectories at 300 K remain defect-free throughout the simulation (a total of 245 ps). Not surprisingly, this percentage decreases at higher temperatures. Thus, at lower temperature there is a greater likelihood of achieving chiralitycontrolled SWCNT growth using a C2H growth agent. However, Figure 4 shows that, irrespective of temperature, defects become more prevalent during C2H-driven SWCNT growth. This is attributed to the increasing presence of carbon radicals on the edge of the growing SWCNT structure (formed via the abstraction of hydrogen from the SWCNT by C2H).


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Figure 4. Percentage of trajectories (out of 120) in which new pentagons and hexagons are formed at 300 K, 500 K, and 800 K.

The C2H radical, formed via pyrolytic or catalytic decomposition of acetylene, is anticipated to be present only in trace quantities under typical CVD growth conditions. We therefore turn to a discussion of the role of C2H2 during SWCNT growth. As C2H2 is the predominant growth agent, SWCNT growth ACS Paragon Plus Environment

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may correspond to repeated DA cycloaddition at armchair sites on the SWCNT edge. The energetics of this process (Figure 5a) is now well established, and features barriers up to 60 kcal/mol9 that exhibit a strong dependence on SWCNT diameter.10 Within this mechanism of SWCNT growth, temperature can therefore be anticipated to play a critical role. Figure 5b shows the temperature dependence of reaction rate constants for endo/exo C2H2 DA cycloaddition to [6]CPP and subsequent H2 renormalization. It is noted that both endo and exo addition exhibit small rate constants (k1), particularly between 200 and 500 K where they are below 10-15 M-1s-1. In the case of exo insertion of C2H2, this first step is the ratedetermining step – the subsequent rate constant (k2) for the H2 renormalization is on the order of 101 s-1. Thus, even at room temperature, the removal of H2 from the growing SWCNT structure is a labile process. On the other hand, k1 and k2 for endo C2H2 insertion exhibit an equivalent dependence on temperature, and are also more similar in magnitude. However, these rate constants increase dramatically with temperature; at 800 K they are of the order of 10-5. Nevertheless, on this basis DA cycloaddition of C2H2 is unlikely to be the principle mechanism of SWCNT growth below 500 K. At such a temperature, the kinetics of radical-insertion of C2H and radical-assisted DA cycloaddition of C2H2 are instead expected to dominate. Increasing the temperature beyond 500 K, while promoting DA cycloaddition, will by comparison enhance the kinetics of pentagon defect formation more significantly. Chirality-controlled growth necessitates the prevention of defect formation (despite the presence of mechanisms by which defects can be removed),16,17 since the presence of even a single defect will change the overall chirality of the nanotube.18 These simulations therefore suggest that chiralitycontrolled growth is impeded significantly at temperatures above 500 K. However, they do not preclude entirely the existence of SWCNT defects during low temperature growth. The accumulation of such defects observed by Ding and coworkers18 can be explained by the fact that their removal is impeded kinetically at lower temperatures. In conclusion, we have shown that temperature impacts organic-precursor SWCNT growth in two ways: high temperature leads to more efficient growth, but in doing so facilitates more extensive defect formation. For SWCNT growth driven only by C2H radicals, we have shown that room temperature provides the optimal balance between these two phenomena. On the other hand, when SWCNT growth is driven predominantly by acetylene, higher temperature, somewhere near 800 K, is beneficial for SWCNT growth; reaction rate constants for of C2H2-based growth are prohibitively small at lower temperatures. On this basis, we predict the existence of an optimum SWCNT growth temperature that balances the rates of growth and defect formation at a given C2H/C2H2 ratio.


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Figure 5. (a) B3LYP/6-31+G(d) reactive potential energy surface for hexagon addition to [6]CPP precursor and H2 renormalization via DA cycloaddition, free energies shown are at 300K. (b) Temperature dependence of reaction rate constants for hexagon addition (k1) and H2 renormalization (k2). Acknowledgement This work was in part supported by CREST (Core Research for Evolutional Science and Technology) from JST. The authors are grateful for generous supercomputer time at the Institute for Molecular Science (IMS) in Okazaki, Japan.

Supporting Information Details of simulation methods, details of rate constant calculations and hexagon addition pathways. These materials are available free of charge via the internet at http://pubs.acs.org. ACS Paragon Plus Environment

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References (1) Iijima, S. Single-Shell Carbon Nanotubes of 1-nm Diameter. Nature 1993, 363, 603-605 (2) Thess, A.; Lee, R.; Nikolaev, P.; Dai, H.; Petit, P.; Robert, J.; Xu, C.; Lee, Y. H.; Kim, S. G.; Rinzler, A. G. Crystalline Ropes of Metallic Carbon Nanotubes. Science 1996, 273, 483-487 (3) Cheng, H. M.; Li, F.; Sun, X.; Brown, S. D. M.; Pimenta, M. A.; Marucci, A.; Dresselhaus, G.; Dresselhaus, M. S. Bulk Morphology and Diameter Distribution of Single-Walled Carbon Nanotubes Synthesized by Catalytic Decomposition of Hydrocarbons. Chem. Phys. Lett. 1998, 289, 602-610 (4) Bachilo, S. M.; Balzano, L.; Herrera, J. E.; Pompeo, F.; Resasco, D. E.; Weisman, R. B. Narrow (n,m)-Distribution of Single-Walled Carbon Nanotubes Grown using a Solid Supported Catalyst. J. Am. Chem. Soc. 2003, 125, 11186-11187 (5) Vijayaraghavan, A.; Hennrich, F.; Stürzl, N.; Engel, M.; Ganzhorn, M.; Oron-Carl, M.; Marquardt, C. W.; Dehm, S.; Lebedkin, S.; Kappes, M. M. Toward Single-Chirality Carbon Nanotube Device Arrays. ACS Nano 2010, 4, 2748-2754 (6) Liu, J.; Wang, C.; Tu, X.; Liu, B.; Chen, L.; Zheng, M.; Zhou, C. Chirality-Controlled Synthesis of Single-Wall Carbon Nanotubes using Vapour-Phase Epitaxy. Nat. Commun 2012, 3, 1199/1-7 (7) Bunz, U. H. F.; Menning, S.; Martín, N. Para-Connected Cyclophenylenes and Hemispherical Polyarenes: Building Blocks for Single-Walled Carbon Nanotubes? Angew. Chem. Int. Ed. 2012, 51, 7094-7101 (8) Omachi, H.; Nakayama, T.; Takahashi, E.; Segawa, Y.; Itami, K. Initiation of Carbon Nanotube Growth by Well-Defined Carbon Nanorings. Nat. Chem. 2013, 5, 572-576 (9) Fort, E. H.; Scott, L. T. Carbon Nanotubes From Short Hydrocarbon Templates. Energy Analysis of the Diels-Alder Cycloaddition/Rearomatization Growth Strategy. J. Mat. Chem. 2011, 21, 1373-1381 (10) Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. Single-Walled Carbon Nanotube Growth From Chiral Carbon Nanorings: Prediction of Chirality and Diameter influence on Growth Rates. J. Am. Chem. Soc. 2012, 134, 15887-15896 (11) Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. Theoretical Insights into Chirality-Controlled SWCNT Growth From a Cycloparaphenylene Template. ChemPhysChem 2012, 13, 1479-1485 (12) Rudenko, A. P.; Balandin, A. A.; Zabalotnaya, M. M. Mechanism of Carbon formation in the Decomposition of Methane, Ethane, Ethylene and Acetylene on Silica Gel. Russ. Chem. Bull. 1961, 10, 916-921 (13) Hung, W.-H.; Bernasek, S. L. Adsorption and Decomposition of Ethylene and Acetylene on Fe(100). Surf. Sci. 1995, 339, 272-290 (14) Okada, T.; Kim, Y.; Trenary, M.; Kawai, M. Identification at the Single Molecule Level of C2Hx Moieties Derived from Acetylene on the Pt(111) Surface. J. Phys. Chem. C 2012, 116, 18372-18381 (15) Ohta, Y.; Okamoto, Y.; Irle, S.; Morokuma, K. Temperature Dependence of Iron-Catalyzed Continued Single-Walled Carbon Nanotube Growth Rates: Density Functional Tight-Binding Molecular Dynamics Simulations. J. Phys. Chem. C 2009, 113, 159-169 (16) Page, A. J.; Ohta, Y.; Okamoto, Y.; Irle, S.; Morokuma, K. Defect Healing During SingleWalled Carbon Nanotube Growth: a Density-Functional Tight-Binding Molecular Dynamics investigation. J. Phys. Chem. C 2009, 113, 20198-20207 (17) Kim, J.; Page, A. J.; Irle, S.; Morokuma, K. Dynamics of Local Chirality During SWCNT Growth: Armchair Versus Zigzag Nanotubes. J. Am. Chem. Soc. 2012, 134, 9311-9319 (18) Yuan, Q.; Xu, Z.; Yakobson, B. I.; Ding, F. Efficient Defect Healing in Catalytic Carbon Nanotube Growth. Phys. Rev. Lett. 2012, 108, 245505/1-5


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Temperature Dependence of Catalyst-Free Chirality-Controlled Single

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