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The mechanism and kinetics of single-walled carbon nanotube (SWNT) nucleation from Fe- and Ni-carbide nanoparticle precursors have been investigated using quantum chemical molecular dynamics (QM/MD) methods [1]. It was observed that SWNT nucleation occurred via three distinct stages, viz. the precipitation of the carbon from the metalcarbide, the formation of a “surface/subsurface” carbide intermediate species, and finally the formation of a nascent sp2-hybidrized carbon structure supported by the metal catalyst. The kinetics of SWNT nucleation exhibited distinct dependences on carbon concentration and temperature. In particular, SWNT nucleation from NixCy nanoparticles proceeded more favorably compared to nucleation from FexCy nanoparticles. The stability of the surface/subsurface carbide was also influenced by the phase of the nanoparticle itself. The observations agree well with experimentally available data for SWNT growth on iron and nickel catalyst particles. References [1] A. J. Page et al. J. Am. Chem. Soc. 132, 15699 (2010).
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QM/MD Simulation of SWNT Nucleation on Transition-Metal
Carbide NanoparticlesStephan Irle,1 Alister J. Page,2 Honami Yamane,2 Yasuhito
Ohta,2 Keiji Morokuma2
1Institute for Advanced Research and Department of Chemistry, Nagoya University2Fukui Institute for Fundamental Chemistry, Kyoto University
The 40th Commemorative Fullerene-Nanotubes General Symposium
9 March, 2011
SWNT Synthesis: The Vapour-Liquid-Solid Mechanism
Gavillet et al., J. Nanosci. Nanotech. (2004)
Yoshida et al., Nano. Lett. (2004) Zhu et al., Small (2004) Zhang et al., Appl. Phys. A (2005)
• 1-electron matrix integrals tabulated using spline functions of interatomic distances.
• Repulsive term fitted against B3LYP dissociation curves of training set species.
• Finite electronic temperature (Te) employed.
• MO occupations:
• Variational quantity:
SCC-DFTB:
NCC-DFTB SCC-DFTB AM1 PM3
C20-C36 0.025 0.019 0.035
0.030
C60-C86 0.014 0.014 0.016
0.015
Geometry RMS Errors (Å), Relative to B3LYP/6-31G(d)
NCC-DFTB SCC-DFTB AM1 PM3
C20-C36 0.88 0.93 0.77 0.73
C60-C86 0.97 0.98 0.86 0.84
Relative Energy R2 values, Relative to B3LYP/6-31G(d)
(a) (b) (c)
PW91 0.88 0.93 0.7
7
SCC-DFTB 0.97 0.98 0.8
6
Adhesion Energies (eV/atom) for
Fen-(5,5) SWNT Complexes
SCC-DFTB: M. Elstner et al., Phys. Rev. B, 58, 7260, (1998)(Sc,Co,Ti,Fe,Co,Ni)-C DFTB parameters: G. Zheng et al., J. Chem. Theor. Comp. 3, 1349, (2007)
Density-Functional Tight-Binding Method
NCC-DFTB: 100 atoms, 1 ns
SCC-DFTB: 100 atoms, 0.1 ns
NCC-DFTB:
• 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.
SCC-DFTB/MD Simulation of SWNT Nucleation Fe38 Catalyst
Y. Ohta et al., ACS Nano 3, 3413 (2009)
Yasuhito Ohta
SCC-DFTB/MD Simulation of SWNT Nucleation Fe38 Catalyst
Y. Ohta et al., ACS Nano 3, 3413 (2009)
Yoshida et al., Nano. Lett. (2008)
SCC-DFTB/MD Simulation of SWNT Nucleation Fe38 Catalyst
Y. Ohta et al., ACS Nano 3, 3413 (2009)
SWNT nucleation: driven by 5-/6-membered ring
formation
Fe3C nanoparticle
SWNT ‘cap’ formed without carbide phase...
Ni116 Ni39C77Ni77C39 Ni58C58
SCC-DFTB/MD Simulation of SWNT Nucleation Ni-Carbide Nanoparticle PrecursorPage et al. J. Am. Chem. Soc. 132, 15699
(2010).
Metal-carbide phase ➛ metal/carbon system.
Precipitation of carbon (bulk ➛ surface): < 50 ps.
SWNT Nucleation: < 150 ps.
Fe77C59@1400K-5
Fe77C59@1400K-5
SWNT nucleation mechanism independent of:
• Catalyst Composition (type of transition metal).• Catalyst Size.
• Reaction Temperature.• [C] & carbon source.
Carbide phase ➛ Catalyst/Cap structure in < 300 ps!
Fe/Ni-carbide nanoparticles thermodynamically unstable
at these conditions.
Ni58C58 @ 800 K
Ni58C58 @ 1400 K
Ni58C58 @ 2000 K
SCC-DFTB/MD Simulation of SWNT Nucleation Page et al. J. Am. Chem. Soc. 132, 15699 (2010).
Average SWNT ‘Nucleation Times’ (ps) from Fe/Ni-Carbide Nanoparticles
SCC-DFTB/MD Simulation of SWNT Nucleation Page et al. J. Am. Chem. Soc. 132, 15699 (2010).
Ni-Carbide
Fe-Carbide
Average ‘Carbon Precipitation Times’
(ps),Fe/Ni-Carbide Nanoparticles
SCC-DFTB/MD Simulation of SWNT Nucleation Page et al. J. Am. Chem. Soc. 132, 15699 (2010).
Carbon Precipitation Dynamics @ 800 K
(Ni58C58, Fe58C58)
Ni-Carbide
Fe-Carbide
Liquid
1400 K
2000 KSolid
800 K
Avera
ge L
IAvera
ge L
IAvera
ge L
I
Phase of Catalyst during Nucleation:Fe: liquid > 800 K;
Ni: solid at 800 K, liquid at 1400 K.
SCC-DFTB/MD Simulation of SWNT Nucleation Page et al. J. Am. Chem. Soc. 132, 15699 (2010).
Ding, Eur. Phys. J. D (2005)
Departure from linearity in L.I.
Melting of Nanoparticles: The Lindemann Index
•SWNT nucleation dynamics: •Driven by ‘catalyst-carbon’ interaction strength. •Catalyst-carbon interactions: Ni-C=1.06 eV; Fe-C=1.78 eV.•Fe-carbide: SWNT nucleation impeded (destruction of C-C bonds).•Ni-carbide: SWNT nucleation enhanced by presence of long carbyne chains
•Catalytically active state of metal particles:•metallic phase, cf. Anisimov et al. Carbon 48, 380 (2010)
•carbide phase not necessary for nucleation•carbide phase not stable for small particles, cf. Harutyunyan et al.
“Reduced carbon solubility in Fe Nanoclusters and Implications for Carbon Nanotube Growth”, Phys. Rev. Lett. 100, 195502 (2008)
ConclusionsPage et al. J. Am. Chem. Soc. 132, 15699 (2010).