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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
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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
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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
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Prolog Our QM/MD StudiesADVERTISEMENT
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)
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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
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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
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Overview
Overview: CCVD SWCNT synthesis
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp7
7
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• 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.
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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
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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
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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
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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
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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
13J. Kim, SI, K. Morokuma, Phys. Rev. Lett. 107, 15505 (2011).
Overview Chirality-controlled CCVD
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Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38
14J. 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
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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
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Slow simulations of (5,5) and (8,0) SWCNT growth on Fe38
16J. 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
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“Confirmation” of Defect/Healing Growth by Experiment
17
Carbon 50, 2407 (2012)
cf: DFTB/MD growth model
Overview Experimental
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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
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Overview
Metal-free SWCNT synthesis from templates
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp19
19
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20
Catalyst-free growth Growth from C60
Nano Lett. 10, 3343 (2010)
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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
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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
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23
SWCNT growth from [n]cycloparaphenylenes
We have a dream:
Omachi, Matsuura, Segawa, Itami, Angew. Chem. Int. Ed. 49, 10202 (2011)
Prof. ItamiNagoya University
Catalyst-free growth Growth from CPPs
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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) SWCNT1. Diels-Alder (DA)
Cycloaddition
2. H2 removal,
Re-aromatization
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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
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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
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Catalyst-free growth Growth from CPPs
27
“Solution” to high barrier: Vapor phase pyrolysis
C2H radical (ethynyl) …
… as initiator of Diels-Alder C2H2 growth
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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
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Growth from CPPs DFTB/MD Methodology
29
QM/MD simulations of [6]CPP growth to (6,6) SWCNTH. 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
SWCNT growth.
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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
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Growth from CPPs DFTB/PRMD Simulations
31
QM/MD simulations of [6]CPP growth to (6,6) SWCNTH. Li, A. J., Page, SI, K. Morokuma, ChemPhysChem 13, 1479 (2012)
485 ps, each
frame = 0.2 ps
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Growth from CPPs DFTB/PRMD Simulations
32
Growth mechanism of C2H and C2H2 addition to CPPsH. 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
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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!
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Growth from CPPs DFTB/PRMD Simulations
34
Availability of extended (5,5) SWCNT capL. T. Scott et al., J. Am. Chem. Soc. 134, 107 (2012)
X-ray structure
Worth a try.
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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
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SWCNT growth from chiral organic nanorings
Omachi, Segawa, Itami, Acc. Chem. Res. (2012)
Prof. ItamiNagoya University
Growth from CPPs Chiral SWCNT growth
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Growth from CPPs DFTB/MD Methodology
37
QM/MD simulations of chiral SWCNTs from CPPsH. 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
SWCNT growth.
(6,6)(8,0)
(4,3) (6,1)
(6,5) (10,1)
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Growth from CPPs DFTB/MD Methodology
38
QM/MD simulations of chiral SWCNTs from CPPsH. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012)
(6,5)
(10,1)
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Growth from CPPs DFTB/MD Methodology
39
QM/MD simulations of chiral SWCNTs from CPPsH. 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 76/3
c) growth proceeds at
armchair edge
3. Growth mechanism in PRMD
follows Ding/Yakobson’s Screw-
dislocation-like (SDL) theory,
PNAS 106, 2506 (2009)
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Growth from CPPs DFTB/MD Methodology
40
Growth termination for (8,0) SWCNTH. Li, A. J., Page, SI, K. Morokuma, J. Am. Chem. Soc. 134, 15887 (2012)
“heptagon-first” 76/3New hexagon
@armchair
B3LYP/6-31G(d)
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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)
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Growth from CPPs DFTB/MD Methodology
42
C2H2-(DA)hexagon addition rates in (n,n) SWCNTs: k ~ dH. 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)
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Overview
Summary: What did we learn?
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp43
43
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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:
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Summary What did we learn?
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• 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)!!
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Overview
What is next?
http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp46
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CNT formation Interpretation
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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.
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CNT formation Interpretation
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Appendix
Appendix
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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
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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
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Experiments for individual SWCNT nucleation and growth
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Nat. Mater. 11, 231 (2012)
Measuring growth rates v of individual SWCNTs by Raman
Overview Experimental evidence
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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
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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
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TimescalePRMD
Parallel Replica MD [A. F. Voter, PRB 57, R13985 (1998)]
Disadvantage: computationally very expensiveAlternatives: Metadynamics, umbrella sampling, etc.
Problem there: MD depends on algorithm/bias potential