SWCNT Growth from Chiral and Achiral Carbon
Nanorings: Prediction of Chirality and Diameter
Influence on Local Growth Rate...
Kyoto University Nagoya University
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp
Dr. Alister J. Page...
Computer resources :
CREST grant 2006-2012
(KM, SI) and AFOSR (to KM)
Funding :
MEXT Tenure Track program, JSPS Kiban (SI)...
Prolog Our QM/MD Studies
ADVERTISEMENT
4
“What can be controlled is never completely real;
what is real can never be compl...
Goal SWCNT Chirality Control
The goal: arbitrary (n,m)-specific SWCNT Growth
(5,5) SWCNT
high yield, desired length, defec...
Overview
 Overview: CCVD SWCNT synthesis
 Metal-free SWCNT synthesis from templates
 Theoretical Simulations of SWCNT g...
Overview
 Overview: CCVD SWCNT synthesis
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp7
7
• SCC-DFTB; Te = 10,000 K.
• MD; ∆t=1 fs.
• NVT ensemble; Tn= 1,500 K.
• Nosé-Hoover-Chain thermostat.
• 30 C2 deposited o...
C2 shooting and annealing on Fe38 particle
9
Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009)
Ove...
Yoshida et al., Nano. Lett. (2008)
SWCNT nucleation:
driven by 5-/6-membered ring formation
from sp carbon
Fe3C nanopartic...
Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009)
“Random” cap structures in CCVD simulations
11
O...
Carbon Feeding Rate Effect: M38C40+nC
A. Page, S. Minami, Y. Ohta, SI, K. Morokuma, Carbon 48, 3014 (2010)
Timescale
probl...
Local Chirality Index (LOCI): Definition
Requires: i) System’s global principal axis in tube direction (GPAZ)
ii) Hexagon’...
Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38
14
J. Kim, A. J. Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 93...
Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38
CNT formation Interpretation
15
Overview Chirality-controlled CCV...
Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38
16
J. Kim, A. J. Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 93...
“Confirmation” of Defect/Healing Growth by Experiment
17
Carbon 50, 2407 (2012)
cf: DFTB/MD growth model
Overview Experime...
Consensus among experimentalists and theoreticians:
18
Overview Summary of CCVD
• Chirality-controlled nucleation on Fe or...
Overview
 Metal-free SWCNT synthesis from templates
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp19...
20
Catalyst-free growth Growth from C60
Nano Lett. 10, 3343 (2010)
Nano Lett. 10, 3343 (2010)
Raman spectra AFM image
=248 cm-1 nm  d = 0.86 nm
0.69 nm  SWCNTs are not strictly
extensions...
J. Liu, C. Wang et al.:
Vapor-phase “epitaxy”
of SWCNTs
Nat. Commun. (2012)
2000 sccm CH4, 300 sccm H2, 900°C, 15 mins
Chi...
23
SWCNT growth from [n]cycloparaphenylenes
We have a dream:
Omachi, Matsuura, Segawa, Itami, Angew. Chem. Int. Ed. 49, 10...
24
SWCNT growth from [n]cycloparaphenylenes: Diels-Alder
Catalyst-free growth Growth from CPPs
E. H. Fort, L. T. Scott, J....
DA barrier heights for C2H2 +
E. H. Fort, L. T. Scott, J. Mater. Chem. 21, 1373 (2011)
Barriers very high!
(many other pro...
Catalyst-free growth Growth from CPPs
26
“Solution” to high barrier: Vapor phase pyrolysis
A. P. Rudenko, A. A. Balandin, ...
Catalyst-free growth Growth from CPPs
27
“Solution” to high barrier: Vapor phase pyrolysis
C2H radical (ethynyl) …
… as in...
Overview
 Theoretical Simulations of SWCNT growth from CPPs
 (n,n) SWCNT growth from [n]CPPs
http://kmweb.fukui.kyoto-u....
Growth from CPPs DFTB/MD Methodology
29
QM/MD simulations of [6]CPP growth to (6,6) SWCNT
H. Li, A. J., Page, SI, K. Morok...
30
Four possible sites for initial H abstraction or
C2H radical addition (sample: 100 trajectories)
42 39
17 1
Number of t...
Growth from CPPs DFTB/PRMD Simulations
31
QM/MD simulations of [6]CPP growth to (6,6) SWCNT
H. Li, A. J., Page, SI, K. Mor...
Growth from CPPs DFTB/PRMD Simulations
32
Growth mechanism of C2H and C2H2 addition to CPPs
H. Li, A. J., Page, SI, K. Mor...
Growth from CPPs DFTB/PRMD Simulations
33
Growth speed of “CPP ring” versus “SWCNT belt”
H. Li, A. J., Page, SI, K. Moroku...
Growth from CPPs DFTB/PRMD Simulations
34
Availability of extended (5,5) SWCNT cap
L. T. Scott et al., J. Am. Chem. Soc. 1...
Overview
 Theoretical Simulations of SWCNT growth from CPPs
 (n,m) SWCNT growth from chiral CPPs
http://kmweb.fukui.kyot...
36
SWCNT growth from chiral organic nanorings
Omachi, Segawa, Itami, Acc. Chem. Res. (2012)
Prof. Itami
Nagoya University
...
Growth from CPPs DFTB/MD Methodology
37
QM/MD simulations of chiral SWCNTs from CPPs
H. Li, A. J., Page, SI, K. Morokuma, ...
Growth from CPPs DFTB/MD Methodology
38
QM/MD simulations of chiral SWCNTs from CPPs
H. Li, A. J., Page, SI, K. Morokuma, ...
Growth from CPPs DFTB/MD Methodology
39
QM/MD simulations of chiral SWCNTs from CPPs
H. Li, A. J., Page, SI, K. Morokuma, ...
Growth from CPPs DFTB/MD Methodology
40
Growth termination for (8,0) SWCNT
H. Li, A. J., Page, SI, K. Morokuma, J. Am. Che...
Growth from CPPs DFTB/MD Methodology
41
C2H-hexagon addition rates consistent with k ~ sin(
H. Li, A. J., Page, SI, K. Mor...
Growth from CPPs DFTB/MD Methodology
42
C2H2-(DA)hexagon addition rates in (n,n) SWCNTs: k ~ d
H. Li, A. J., Page, SI, K. ...
Overview
 Summary: What did we learn?
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp43
43
Summary What did we learn?
44
• C2H radicals are feasible via C2H2 pyrolysis on SiO2.
• C2H radicals are able to remove H ...
Summary What did we learn?
45
• DA C2H2 implies hexagon addition rates k ~ d.
• At given C2H/C2H2 ratio, there should be o...
Overview
 What is next?
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp46
46
CNT formation Interpretation
47
What is next?
Theoreticians need to address the following urgent issues:
-Timescale proble...
CNT formation Interpretation
48
Appendix
Appendix
D. A. Gomez-Gualdron, G. D. McKenzie, J. F. J. Alvarado, P. B. Balbuena ACS Nano 6, 720 (2012)
“Random” cap structures in ...
Experiments for individual SWCNT nucleation and growth
50
Nat. Mater. 11, 231 (2012)
Measuring growth rates v of individua...
Nano Lett. 10, 3343 (2010)
Notes:
•baked at 150° in air to remove
solvent (toluene)
•Thermal oxidation in air at 300-
500°...
52
Scheme to study AC CNT growth by adding C2H radicals
(1) Starts from one initial structure, and then add 6 times C2H ra...
53/25
TimescalePRMD
Parallel Replica MD [A. F. Voter, PRB 57, R13985 (1998)]
Disadvantage: computationally very expensive
...
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SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates

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Catalyst-free, chirality-controlled growth of chiral and achiral single-walled carbon nanotubes (SWCNTs) from organic precursors is demonstrated using quantum chemical simulations [1]. Growth of (4,3), (6,5), (6,1), (10,1), (6,6) and (8,0) SWCNTs was induced by ethynyl radical (C2H) addition to organic precursors. These simulations show a strong dependence of the SWCNT growth rate on the chiral angle, θ. The SWCNT diameter however does not influence the SWCNT growth rate under these conditions. This agreement with a previously proposed screw-dislocation-like model of transition metal-catalyzed SWCNT growth rates [2] indicates that the SWCNT growth rate is an intrinsic property of the SWCNT edge itself. Conversely, we predict that the rate of local SWCNT growth via Diels-Alder cycloaddition of C2H2 is strongly influenced by the diameter of the SWCNT. We therefore predict the existence of a maximum local growth rate for an optimum diameter/chirality combination at a given C2H/C2H2 ratio. We also find that the ability of a SWCNT to avoid defect formation during growth is an intrinsic quality of the SWCNT edge.

References:

[1] Li, H.-B.; Page, A. J.; Irle, S.; Morokuma, K. J. Am. Chem. Soc. 2012, 134, 15887-15896.
[2] Ding, F.; Harutyunyan, A. R.; Yakobson, B. I. Proc. Natl. Acad. Sci. 2009, 106, 2506-2509.

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SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates

  1. 1. SWCNT Growth from Chiral and Achiral Carbon Nanorings: Prediction of Chirality and Diameter Influence on Local Growth Rates Stephan Irle,1 Hai-Bei Li,2 Alister J. Page,2 Keiji Morokuma2,3 2Kyoto University 1Nagoya University http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp The Sixth Rice University, Air Force Research Laboratory, NASA, Honda Research Institute Workshop on Nucleation and Growth Mechanisms of Single Wall Carbon Nanotubes The Flying L Ranch, Bandera, TX, U.S.A., April 13, 2013 3
  2. 2. Kyoto University Nagoya University http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp Dr. Alister J. Pageb Acknowledgements Prof. Keiji Morokuma Dr. Hai-Bei Libnow: Lecturer, University of Newcastle (AUS) Dr. Joonghan Kim 2 2
  3. 3. Computer resources : CREST grant 2006-2012 (KM, SI) and AFOSR (to KM) Funding : MEXT Tenure Track program, JSPS Kiban (SI) Acknowledgements Research Center for Computational Science (RCCS), Okazaki Research Facilities, National Institutes for Natural Sciences. Academic Center for Computing and Media Studies (ACCMS), Kyoto University 3
  4. 4. Prolog Our QM/MD Studies ADVERTISEMENT 4 “What can be controlled is never completely real; what is real can never be completely controlled.” Vladimir V. Nabokov, in: Look at the harlequins! McGraw- Hill, New York (1974)
  5. 5. Goal SWCNT Chirality Control The goal: arbitrary (n,m)-specific SWCNT Growth (5,5) SWCNT high yield, desired length, defect-free, eventually catalyst-free ACCVD etc … Selection of “appropriate” growth conditions diameter yield chirality length 5
  6. 6. Overview  Overview: CCVD SWCNT synthesis  Metal-free SWCNT synthesis from templates  Theoretical Simulations of SWCNT growth from CPPs  (n,n) SWCNT growth from [n]CPPs  (n,m) SWCNT growth from chiral CPPs  Summary: What did we learn?  What is next? http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp6 6
  7. 7. Overview  Overview: CCVD SWCNT synthesis http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp7 7
  8. 8. • SCC-DFTB; Te = 10,000 K. • MD; ∆t=1 fs. • NVT ensemble; Tn= 1,500 K. • Nosé-Hoover-Chain thermostat. • 30 C2 deposited onto fcc-Fe38 surface (1/ps). • NVT thermal annealing for 400 ps. Yasuhito Ohta Overview DFTB/MD of cap nucleation C2 shooting and annealing on Fe38 particle 8 Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009) • 10 trajectory replica.
  9. 9. C2 shooting and annealing on Fe38 particle 9 Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009) Overview DFTB/MD of cap nucleation Pentagon-first mechanism
  10. 10. Yoshida et al., Nano. Lett. (2008) SWCNT nucleation: driven by 5-/6-membered ring formation from sp carbon Fe3C nanoparticle Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009) C2 shooting and annealing on Fe38 particle 10 Overview DFTB/MD of cap nucleation Cap structures are relatively random even in “slow” MD simulations
  11. 11. Y. Ohta, Y. Okamoto, A. J. Page, SI, K. Morokuma, ACS Nano 3, 3413 (2009) “Random” cap structures in CCVD simulations 11 Overview DFTB/MD of cap nucleation Cap structures are relatively random even in “slow” DFTB/MD simulations
  12. 12. Carbon Feeding Rate Effect: M38C40+nC A. Page, S. Minami, Y. Ohta, SI, K. Morokuma, Carbon 48, 3014 (2010) Timescale problem in MD 12 Overview Sidewall growth, defects unpublished
  13. 13. Local Chirality Index (LOCI): Definition Requires: i) System’s global principal axis in tube direction (GPAZ) ii) Hexagon’s local principal axis normal to hexagon plane Local chiral angle 1 13 J. Kim, SI, K. Morokuma, Phys. Rev. Lett. 107, 15505 (2011). Overview Chirality-controlled CCVD
  14. 14. Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38 14 J. Kim, A. J. Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 9311 (2012). +30C 300 ps, 1500K +30C 300 ps, 1500 K Error bars: Standard deviation Trajectory B Trajectory A Overview Chirality-controlled CCVD
  15. 15. Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38 CNT formation Interpretation 15 Overview Chirality-controlled CCVD J. Kim, A. J. Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 9311 (2012). +30C 300 ps, 1500K +30C 300 ps, 1500 K Error bars: Standard deviation Trajectory D Trajectory D
  16. 16. Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38 16 J. Kim, A. J. Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 9311 (2012). Statistics based on 10 trajectoriesa Conclusions: (5,5) grows less defects than (8,0), heals faster! Overview Chirality-controlled CCVD
  17. 17. “Confirmation” of Defect/Healing Growth by Experiment 17 Carbon 50, 2407 (2012) cf: DFTB/MD growth model Overview Experimental
  18. 18. Consensus among experimentalists and theoreticians: 18 Overview Summary of CCVD • Chirality-controlled nucleation on Fe or Ni nanoparticles is difficult! Higher temperature gives “cleaner” tubes • Growth occurs on “long” timescales (carbon atom addition on nanosecond scale) • Atomically faster growth (=higher feedstock pressure) increases concentration of tube defects Suggested solutions: • Avoid catalyst for nucleation, • grow sidewalls in low pressure, high temperature • from templates with established (n,m) chiral structure
  19. 19. Overview  Metal-free SWCNT synthesis from templates http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp19 19
  20. 20. 20 Catalyst-free growth Growth from C60 Nano Lett. 10, 3343 (2010)
  21. 21. Nano Lett. 10, 3343 (2010) Raman spectra AFM image =248 cm-1 nm  d = 0.86 nm 0.69 nm  SWCNTs are not strictly extensions of C60 cap; C30 too small? RBM=288 cm-1 Tube length: 40 m mentioned Catalyst-free growth Growth from C60 21
  22. 22. J. Liu, C. Wang et al.: Vapor-phase “epitaxy” of SWCNTs Nat. Commun. (2012) 2000 sccm CH4, 300 sccm H2, 900°C, 15 mins Chirality confirmed; more successful! Catalyst-free growth Growth from CNTs 22 22 J. Zhang, Z. F. Liu et al.: “Cloning” of SWCNTs Nano Lett. 9, 1673 (2009) 100 sccm CH4, 5 sccm C2H4, 975°C, 15 mins Extension was short, maintenance of chirality not proven
  23. 23. 23 SWCNT growth from [n]cycloparaphenylenes We have a dream: Omachi, Matsuura, Segawa, Itami, Angew. Chem. Int. Ed. 49, 10202 (2011) Prof. Itami Nagoya University Catalyst-free growth Growth from CPPs
  24. 24. 24 SWCNT growth from [n]cycloparaphenylenes: Diels-Alder Catalyst-free growth Growth from CPPs E. H. Fort, L. T. Scott, J. Mater. Chem. 21, 1373 (2011), also cited by Wang & Liu Basic idea: Example: (5,5) SWCNT 1. Diels-Alder (DA) Cycloaddition 2. H2 removal, Re-aromatization
  25. 25. DA barrier heights for C2H2 + E. H. Fort, L. T. Scott, J. Mater. Chem. 21, 1373 (2011) Barriers very high! (many other processes may compete) Catalyst-free growth Growth from CPPs 25
  26. 26. Catalyst-free growth Growth from CPPs 26 “Solution” to high barrier: Vapor phase pyrolysis A. P. Rudenko, A. A. Balandin, M. M. Zabolotnaya, Russ. Chem. Bull. 10, 916 (1961) Carbon production on SiO2 from: CH4 C2H6 C2H4 C2H2
  27. 27. Catalyst-free growth Growth from CPPs 27 “Solution” to high barrier: Vapor phase pyrolysis C2H radical (ethynyl) … … as initiator of Diels-Alder C2H2 growth
  28. 28. Overview  Theoretical Simulations of SWCNT growth from CPPs  (n,n) SWCNT growth from [n]CPPs http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp28 28
  29. 29. Growth from CPPs DFTB/MD Methodology 29 QM/MD simulations of [6]CPP growth to (6,6) SWCNT H. Li, A. J., Page, SI, K. Morokuma, ChemPhysChem 13, 1479 (2012) • SCC-DFTB: Te = 1,500 K. • MD; t=0.5 fs. • NVT ensemble; Tn = 500 K. • Nose-Hoover-Chain thermostat. • Initial annealing of CPP for 5 ps. • 1 C2H2 added every 10 ps with near random edge- carbon. • (Optional) manual hydrogen removal at initial stage of
  30. 30. 30 Four possible sites for initial H abstraction or C2H radical addition (sample: 100 trajectories) 42 39 17 1 Number of trajectories Growth from CPPs Preliminary studies
  31. 31. Growth from CPPs DFTB/PRMD Simulations 31 QM/MD simulations of [6]CPP growth to (6,6) SWCNT H. Li, A. J., Page, SI, K. Morokuma, ChemPhysChem 13, 1479 (2012) 485 ps, each frame = 0.2 ps
  32. 32. Growth from CPPs DFTB/PRMD Simulations 32 Growth mechanism of C2H and C2H2 addition to CPPs H. Li, A. J., Page, SI, K. Morokuma, ChemPhysChem 13, 1479 (2012) Level: B3LYP/6-31G(d) DA: High barrier Radical initiation: It only takes 1 C2H! Radical pathways: low- energy
  33. 33. Growth from CPPs DFTB/PRMD Simulations 33 Growth speed of “CPP ring” versus “SWCNT belt” H. Li, A. J., Page, SI, K. Morokuma, ChemPhysChem 13, 1479 (2012) Conformational flexibility of CPPs hinders growth!
  34. 34. Growth from CPPs DFTB/PRMD Simulations 34 Availability of extended (5,5) SWCNT cap L. T. Scott et al., J. Am. Chem. Soc. 134, 107 (2012) X-ray structure Worth a try.
  35. 35. Overview  Theoretical Simulations of SWCNT growth from CPPs  (n,m) SWCNT growth from chiral CPPs http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp35 35
  36. 36. 36 SWCNT growth from chiral organic nanorings Omachi, Segawa, Itami, Acc. Chem. Res. (2012) Prof. Itami Nagoya University Growth from CPPs Chiral SWCNT growth
  37. 37. Growth from CPPs DFTB/MD Methodology 37 QM/MD simulations of chiral SWCNTs from CPPs H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) • SCC-DFTB: Te = 1,500 K. • MD; t=0.5 fs. • NVT ensemble; Tn = 500 K. • Nose-Hoover-Chain thermostat. • Initial annealing of CPP for 5 ps. • 1 C2H2 added every 10 ps with near random edge- carbon. • (Optional) manual hydrogen removal at initial stage of (6,6) (8,0) (4,3) (6,1) (6,5) (10,1)
  38. 38. Growth from CPPs DFTB/MD Methodology 38 QM/MD simulations of chiral SWCNTs from CPPs H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) (6,5) (10,1)
  39. 39. Growth from CPPs DFTB/MD Methodology 39 QM/MD simulations of chiral SWCNTs from CPPs H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) 1. Addition of new hexagons exclusively in armchair bay 2. In case of pure zigzag edge, a) formation of heptagon b) followed by 76/3 c) growth proceeds at armchair edge 3. Growth mechanism in PRMD follows Ding/Yakobson’s Screw- dislocation-like (SDL) theory, PNAS 106, 2506 (2009)
  40. 40. Growth from CPPs DFTB/MD Methodology 40 Growth termination for (8,0) SWCNT H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) “heptagon-first” 76/3 New hexagon @armchair B3LYP/6-31G(d)
  41. 41. Growth from CPPs DFTB/MD Methodology 41 C2H-hexagon addition rates consistent with k ~ sin( H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) =27° =25° =5° =8° Indeed, for C2H addition in PRMD, armchair edge is a “cozy corner!” Ding/Yakobson’s Screw- dislocation-like (SDL) model, PNAS 106, 2506 (2009)
  42. 42. Growth from CPPs DFTB/MD Methodology 42 C2H2-(DA)hexagon addition rates in (n,n) SWCNTs: k ~ d H. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012) endo exo DA barrier H2 removal barrier B3LYP/6-31G(d)
  43. 43. Overview  Summary: What did we learn? http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp43 43
  44. 44. Summary What did we learn? 44 • C2H radicals are feasible via C2H2 pyrolysis on SiO2. • C2H radicals are able to remove H and add to SWCNTs with little barrier. • C2H radicals may initiate radical edge “polymerization”. • Growth by C2H addition is controlled by SWCNT edge structure alone “Radically” New Chemistry: • New hexagons are formed always near armchair site (=“cozy corner” in Ding/Yakobson SDL-model) Growth Mechanism in PRMD simulations:
  45. 45. Summary What did we learn? 45 • DA C2H2 implies hexagon addition rates k ~ d. • At given C2H/C2H2 ratio, there should be optimal growth conditions for certain d, combinations. C2H/C2H2 ratio may allow control of arbitrary (n,m)!!
  46. 46. Overview  What is next? http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp46 46
  47. 47. CNT formation Interpretation 47 What is next? Theoreticians need to address the following urgent issues: -Timescale problem in MD simulations, e.g. by KMC, will allow to study: -Role of carbide formation -Role of defect healing -More precise atomistic growth mechanisms (no timescale problem of MD, no arbitrariness as in PRMD) -Investigate possible mechanism for chirality control at time of nucleation -Investigate role of hydrogen in greater detail -Effect of various catalyst substrates in atomic detail -Effect of etching gases and water Thank you.
  48. 48. CNT formation Interpretation 48 Appendix Appendix
  49. 49. D. A. Gomez-Gualdron, G. D. McKenzie, J. F. J. Alvarado, P. B. Balbuena ACS Nano 6, 720 (2012) “Random” cap structures in CCVD simulations 49 Overview SIMCAT/MD of cap nucleation Cap structures are relatively random even in “slower” SIMCAT/MD simulations Classical reactive MD simulations of cap formation on supported Nix
  50. 50. Experiments for individual SWCNT nucleation and growth 50 Nat. Mater. 11, 231 (2012) Measuring growth rates v of individual SWCNTs by Raman Overview Experimental evidence
  51. 51. Nano Lett. 10, 3343 (2010) Notes: •baked at 150° in air to remove solvent (toluene) •Thermal oxidation in air at 300- 500°C for 30 mins •Remove “amorphous carbon”: Temperature up to 900°C in presence of water, then cool down •900°C annealing for 3 mins (presumably in vacuum) •20 mins 20 sccm ethanol in 30 sccm Ar/H2 at 900°C (low sccm!) Catalyst-free growth Growth from C60 51
  52. 52. 52 Scheme to study AC CNT growth by adding C2H radicals (1) Starts from one initial structure, and then add 6 times C2H radical to obtain 6 parallel trajectories every 10 ps; (2) Select two trajectories that could produce uniform AC NT to continue. Principles for rule (2):  First, whether new 6-m ring formed;  Then whether C2H insert to the edge of SWCNT;  Then whether H atoms on the rim of SWCNT abstracted  Then whether H atoms on the sidewall of SWCNT abstracted  Then whether C2H added to sidewall
  53. 53. 53/25 TimescalePRMD Parallel Replica MD [A. F. Voter, PRB 57, R13985 (1998)] Disadvantage: computationally very expensive Alternatives: Metadynamics, umbrella sampling, etc. Problem there: MD depends on algorithm/bias potential

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