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

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

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

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

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)

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

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

Overview
 Overview: CCVD SWCNT synthesis
7

• 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
Pentagon-first mechanism

Yoshida et al., Nano. Lett. (2008)
SWCNT nucleation:
driven by 5-/6-membered ring formation
from sp carbon
Fe3C nanoparticle
10
Cap structures are relatively random even in “slow” MD simulations

“Random” cap structures in CCVD simulations
11
Cap structures are relatively random even in “slow” DFTB/MD simulations

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

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

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

CNT formation Interpretation
15
+30C
300 ps, 1500K
+30C
300 ps, 1500 K
Error bars: Standard deviation
Trajectory D
Trajectory D

16
Statistics based on 10 trajectoriesa
Conclusions: (5,5) grows less defects than (8,0), heals faster!

“Confirmation” of Defect/Healing Growth by Experiment
17
Carbon 50, 2407 (2012)
cf: DFTB/MD growth model
Overview Experimental

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

Overview
 Metal-free SWCNT synthesis from templates
19

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 of C60 cap; C30 too small?
RBM=288 cm-1
Tube length: 40 m mentioned
21

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
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
SWCNT growth from [n]cycloparaphenylenes: Diels-Alder
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

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)
25

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
“Solution” to high barrier: Vapor phase pyrolysis
C2H radical (ethynyl) …
… as initiator of Diels-Alder C2H2 growth

Overview
 (n,n) SWCNT growth from [n]CPPs
28

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
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

Growth from CPPs DFTB/PRMD Simulations
31
QM/MD simulations of [6]CPP growth to (6,6) SWCNT
485 ps, each
frame = 0.2 ps

32
Growth mechanism of C2H and C2H2 addition to CPPs
Level: B3LYP/6-31G(d)
DA: High barrier Radical initiation:
It only takes 1 C2H!
Radical pathways: low-
energy

33
Growth speed of “CPP ring” versus “SWCNT belt”
Conformational
flexibility of CPPs
hinders growth!

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.

Overview
 (n,m) SWCNT growth from chiral CPPs
35

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
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
(6,5)
(10,1)

39
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
Growth termination for (8,0) SWCNT
“heptagon-first” 76/3
New hexagon
@armchair
B3LYP/6-31G(d)

41
C2H-hexagon addition rates consistent with k ~ sin(
=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
C2H2-(DA)hexagon addition rates in (n,n) SWCNTs: k ~ d
endo
exo
DA barrier H2 removal barrier
B3LYP/6-31G(d)

Overview
 Summary: What did we learn?
43

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:

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)!!

Overview
 What is next?
46

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
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 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

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

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!)
51

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

53/25
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

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

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