Popov V.N., Lambin P. (eds.) Carbon Nanotubes

Подождите немного. Документ загружается.

205

addressed so that truly large-scale simulations on thousands of processors can

be effectively performed.

ACKNOWLEDGEMENTS

Computations on the methane adsorption on graphene have been performed

with a partial support from HPC-Europe (CINECA, Italy). The results for the

influence of external electric field on defective SWCNT have been calculated

under the Taiwan-Bulgarian project. A Grant from the Ministry of Education

and Science (ɍ-Ɏ-03/03) and a grant from the University of Sofia (2005) have

been used for calculations of mechanical strength of carbon nanotubes.

References

Allan, M., 2005, Excitation of the four fundamental vibrations of CH4 by electron impact near

threshold, J. Phys. B: At. Mol. Opt. Phys. 38:1679-1685.

Baerends, E. J.; Ellis, D. E.; and Ros, P., 1973, Self-consistent molecular Hartree—Fock—Slater

calculations I. The computational procedure, Chem. Phys. 2:41-51.

Bienfait, M., Zeppenfeld, P., Dupont-Pavlovsky, N., Muris, M.R., Wilson, T., DePies, M., and

Vilches, O.E., 2004, Thermodynamics and structure of hydrogen, methane, argon, oxygen,

and carbon dioxide adsorbed on sigle wall carbon naotube bundles, Phys. Rev. B

70:035410/1-10.

Blöchl, P. E., 1994, Projector augmented-wave method, Phys. Rev. B 50:17953-1797.

Blöchl, P. E., 2000, First-principles calculations of defects in oxygen-deficient silica exposed to

hydrogen Phys. Rev. B 62:6158-6179.

Car, R., Parrinello, M., 1985, Unified approach for Molecular Dynamics and Density-Functional

Theory, Phys. Rev. Lett. 55:2471-2474.

Chelikowsky, J. R., 2000, The pseudopotential-density functional method applied to

nanostructures,

J. Phys. D: Appl. Phys. 33:R33-R50 http://jrc.cems.umn.edu/codes.htm.

Collins, P. G., Bradley, K., Ishigami, M., and Zettl, A., 2000, Extreme Oxygen Sensitivity of

electron properties of carbon nanotubes, Science 287:1801-1804.

Curtarolo, Stefano, 2003, Coarse-Graining and Data Mining Approaches to the prediction of

structures and their dynamics, Ph.D. Thesis, MIT (USA).

Daykov, I., and Proykova, A., 2001, Cluster size dependence of the temperature interval of

coexisting phases observed in plastic molecular clusters, in: Meetings in Physics at University

of Sofia, A. Proykova, ed., vol. 2, Heron Press Science Series, Sofia, pp. 31-35.

Daykova, E., Pisov, S., and Proykova, A., 2005, First-principles and molecular dynamics

simulations of methane adsorption on graphene, NATO Science Series II, Springer,

submitted.

Daykova, E. , Proykova, A., and Ohmine, I., 2002, Statistical Calculations of Entropy of Methane

Clathrate, in: Meetings in Physics @ University of Sofia, A. Proykova, ed., vol. 3, Heron

Press Science Series, Sofia, pp. 44 -48.

Durgun, E., Dag, S., Bagci, V. M. K., Gulseren, O., Yildirim, T., and Ciraci, S., 2003, Systematic

study of adsorption of single atoms on a carbon nanotube, Phys. Rev. B 67:201401-201404.

206

Garao, C., Frontera, A., Quinonero, D., Costa, A., Ballester, P., Deya, P.M., 2003, Lithium

diffusion in single-walled carbon nanotubes: a theoretical study, Chem. Phys. Lett. 374:548-

553.

Ghoniem, N., Busso, E., Kiossis, N., and Huang, H., 2003, Multiscale modeling of

nanomechanics and micromechanics: an overview, Philosophical Magazine 83:3475-3528.

Hertel, T., Kriebel, J., Moos, G., and Fasel, R., 2001, Adsorption and desorption of weakly

bonded adsorbates from single-wall carbon nanotube bundles, AIP Conference Proceedings

590, Nanonetwork Materials, Fullerenes, Nanotubes and Related Systems, S. Saito, T. Ando,

Y. Iwasa, K. Kikuchi, M. Kobayashi, Y. Saito, eds., Kamakura, Japan, p.181.

Hill, T. L., 1987, Statistical Mechanics: Principles and Selected Applications, Dover, New York.

Hill, T. L., 1986, An Introduction to Statistical Thermodynamic,.Dover, New York.

Hill, T. L., 1994, Thermodynamics of Small Systems, Parts I and II, Two Volumes in One. Dover,

New York.

Iliev, H., and Proykova, A., 2004, Mechanically induced defects in single-wall carbon nanotubes,

in Meetings in Physics at University of Sofia, A. Proykova, ed., vol. 5, Heron Press Science

Series, Sofia, pp. 87-91.

Iliev, H., Li, F.-Yin, and Proykova, A., 2005, Carbon nanotubes with vacancies under external

mechanical stress and electric field, NATO Science Series II, Springer, submitted.

Kadanoff, L. P., 1976, Notes on Migdal's Recursion Formulas, Ann. Phys. 100:359-394.

Kadanoff, L. P., 1977, The Application of Renormalization Group Techniques to Quarks and

Strings, Rev. Mod. Phys. 49:267-296.

Kleinhammes, A., Mao, S.-H., Yang, X.-J., Tang, X.-P, Shimoda, H., Lu, J.P., Zhou, O., and Wu,

Y., 2003, Gas adsorption in single-walled carbon nanotubes studied by NMR, Phys. Rev. B

68:075418/1-6.

Kong, J., Franklin, N.R., Zhou, C., Chapiline, Peng, S., Cho, K., and Dai, H., 2000, Nanotube

Molecular Wires as Chemical Sensors, Science 287:622-625.

Kohn, W. and Sham, L.J., 1965, Self-consistent equations including exchange and correlation

effects, Phys. Rev. 140:A1133-A1138.

Krasheninnikov, A.V., Nordlund, K., Lehtinen, P.O., Foster, A.S., Ayuela, A., and Nieminen,

R.M., 2004, Adsorption and migration of carbon adatoms on carbon nanotubes: Density-

functional ab initio and tight-binding studies, Phys. Rev. B 69:073402/1-4.

Landman, Uzi and Kleinman, George, 1975, Local and non-local effects in the theory of

physisorption, J. Vac. Sci. Technol. 12:206-209.

Lin, J. S. , Qteish, A., Payne, M. C. and Heine, V., 1993, Optimized and transferable nonlocal

separable ab initio pseudopotentials, Phys. Rev. B 47:4174-4180.

Maiti, A., Brabec, C.J., and Bernholc, J., 1997, Kinetics of metal-catalyzed growth of single-

walled carbon nanotubes, Phys.Rev. B 55:R6097-R6100.

Manfrin, R. (1996) On the gevrey regularity for weakly hyperbolic equations with space-time

degeneration of oleinik type, Rendiconti di Matematica 16:203-231.

Migdal, A.A., 1975, Zh.Eksp. Teor. Fiz. 69:1457.

Moe, Zugang and Susan B. Sinnott, 2001, Separation of Organic Molecular Mixtures in Carbon

Nanotubes and Bundles: Molecular Dynamics Simulations, The University of Kentucky, 177

Anderson Hall, Lexington, Kentucky 40506-0046.

Muris, M., Bienfait, M., Zeppenfeld, P., Dupont-Pavlovsky N., Wass, P., Johnsons, M., Vilches,

O.E., and Wilson, T., 2001, http://www.ill.fr/AR-01/p-82.htm

and references there in

Nosé, S.J., 1984, Constant temperature molecular dynamics methods, J. Chem. Phys. 81:511-519.

Pati, R., Zhang, Y., and Nayak, S., 2002, Effect of H2O adsorption on electron transport in a

carbon nanotube, Appl. Phys. Lett. 81:2638-2640.

207

Perdew, J. and Wang Y., 1992, Accurate and simple analytic representation of the electron-gas

correlation energy, Phys. Rev. B 45:13244-13249.

Perdew, J. P., Chevary, J. A., Vosko, S. H., Jackson, K. A. Pederson, M. R., Singh, D. J., and

Fiolhais, C., 1992, Atoms, molecules, solids, and surfaces: Applications of generalized

gradient approximation for exchange and correlation, Phys.Rev. B 46:6671-6687.

Petrilli, H. M.; Blöchl, P. E.; Blaha, P.; Schwarz, K., 1998, Electric-field-gradient calculations

using the projector augmented wave method, Phys. Rev. B 57:14690-14697.

Proykova, A., Pisov, S., Radev, R., Mihailov, P., Daykov, I., and R. S.Berry, 2001, Dynamical

Phase Coexistence of Molecular Nano-clusters: Kinetics versus Thermodynamics, in:

Nanoscience&Nanotechnolgy, E. Balabanova, I. Dragieva, eds., Heron Press Science Series,

Sofia, pp.18-20.

Proykova, A., 2002, The role of metastable states in the temperature driven phase changes of

molecular nano-clusters, Vacuum 68:97-104.

Proykova, A., Pisov, S., Dragieva, I., and Chelikowski, J., 2003, DFT Calculations of optimized

structures of some coordination compounds, in: Nanoscience&Nanotechnolgy’03, E.

Balabanova, I. Dragieva, eds., Heron Press Science Series, Sofia.

Proykova, A., and Iliev, H., 2004, Simulated stress and stretch of SWCNT, in: Proceedings of

SIMS, B. Elmegaard, J. Sporring, K. Erleben, K. Sorensen, eds., Copenhagen, pp. 273-279.

Shi, Wei and Johnson, J. Karl, 2003, Gas adsorption on Heterogeneous Single-Walled Carbon

Nanotube Bundles, Phys. Rev. Lett. 91:015504/1-4.

Skoulidas, A., Ackerman, D., Johnson, J.K., and Sholl, D., 2002, Rapid transport of gases in

carbon nanotubes, Phys. Rev. Lett. 89:185901/1-4.

Spurling, T. H., De Rocco, A. G., and Storvick, T. S., 1968, Intermolecular Forces in Globular

Molecules. VI. Octopole Moments of Tetrahedral Molecules, J. Chem. Phys. J. Chem. Phys.

48:1006-1008.

Talapatra, S. and Migone, A.D., 2002, Adsorption of methane on bundles of closed-ended single-

wall carbon nanotubes, Phys. Rev. B 65:045416/1-6.

Udomvech, A., Kerdcharoen, T., Osotchan, T., 2005, First principles study of Li and Li+

adsorbed on carbon nanotube: Variation of tubule diameter and length, Chem. Phys. Lett.

406:161-166.

Vassiliev, I., Ogut, S., and Chelikowsky, J. R., 2002, First-principles density-functional

calculations for optical spectra of clusters and nanocrystals, Phys. Rev. B 65:115416/1-18.

Venables, John A., 2000, Introduction to Surface and Thin Film Processes, Cambridge

University Press, Cambridge.

Verlet, L., 1967, Computer "experiments" on classical fluids. I. Thermodynamical properties of

Lennard-Jones molecules, Phys. Rev. 159:98-103.

Zhang, Y. and Dai, H., 2000, Formation of metal nanowires on suspended single-wall carbon

nanotubes, Appl. Phys. Let. 77:3015-3017.

Zhang, Y., Franklin, N. W., Chen, R. J., and Dai, H., 2000a, Metal coating on suspended carbon

nanotubes and its implication to metal-tube interaction, Chem.Phys. Lett. 331:35-41.

*To whom correspondence should be addressed. Dr. Ana Proykova, Department of Atomic Physics,

University of Sofia, 5 James Bourchier Blvd, 1164 Sofia, Bulgaria; e-mail: anap@phys.uni-sofia.bg

209

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 209–210.

FIRST-PRINCIPLES AND MOLECULAR DYNAMICS SIMULATIONS

OF METHANE ADSORPTION ON GRAPHENE

EVGENIYA DAYKOVA, STOYAN PISOV, ANA

PROYKOVA*

Faculty of Physics, University of Sofia, Sofia, Bulgaria

Abstract. First-principle real-space calculations within a time-dependent local

density approximation show fluctuating charge distribution in a methane

molecule physisorbed on a finite-size graphene sheet, which in turn bends

forming a concave surface under multipole-multipole interaction and the carbon

network vibrates in a complex way: a metastable physisorbed state occurs.

Keywords: methane adsorption; graphene; Molecular Dynamics; ab-initio calculation

This paper presents results from first-principles simulations of methane

adsorption on graphene. One aim of the study is to quantify the difference in

adsorption on a graphene sheet compared to adsorption on carbon nanotubes –

perfect and defective. Comparisons show (Stan et al., 1998) a stronger binding

of the adsorbate in the tubes than at the planar surface of graphite. Another goal

is to find out if the adsorption makes a metastable state.

Methane molecules (tetrahedra) resemble rare gases: CH

- CH

interaction

is classically described with a Lennard-Jones potential, inherent for the noble

atoms. Our previous Molecular Dynamics simulations showed that the

interaction energy is orientationally dependent (Daykova et al., 2004). The

current real-space density functional calculations with the Chelikowski’s code

(Chelikowski, 2000) and an ultrasoft pseudopotential for carbon atoms

generated with the fhi98PP code (Kratzer et al., 1998) do not manifest any

dependence of the interaction energy on the CH4 orientation with respect to the

initially flat graphene surface: case "F" with 3 bonds closer to the sheet; case

"V" with 1 bond. The methane molecule is initially located in either "F" or "V"

position above point 0 on the finite piece of a graphene sheet (Fig. 1a). After ~

30 fs of relaxation, the CH

center of mass stabilizes its position above the sheet

210

(Fig. 1b) (the upper curve is for case "F"). The interaction induces a dipole

moment in CH

(Fig. 1c) that fluctuates with the CH

center of mass with a

certain delay due to inertia. Larger moment is produced in case "V". The two

orientations might be Raman distinguishable. The charge distribution at 20%

level of the electron density 60 fs after the run start is presented in Fig. 1d. The

preliminary results show that CH

behaves differently on a tube.

(a)

(b)

(c)

(d)

Figure 1. Initial (a) and stabilized (b) position of the CH

molecule above the graphene sheet, (c)

induced dipole moment of the molecule, and (d) charge distribution of the relaxed configuration.

References

Daykova, E., and Proykova, A., 2004, A peculiar structure of free methane clusters at low

temperatures, Meetings in Physics @ University of Sofia, 5:69-75.

Chelikowsky, J. R., 2000, The pseudopotential-density functional method applied to

nanostructures,

J. Phys. D: Appl. Phys. 33: R33-R50 http://jrc.cems.umn.edu/codes.htm.

Kratzer, P., Morgan, C.G.,Penev, E., Rosa, A.L., Schindlmayr, A.,Wang, L.G.,Zywietz,T.,1998,

Computer code for density-functional theory calculations for poly-atomic systems,

http://www.fhi-berlin.mpg.de/th/fhi98md/fhi98PP/.

Stan, G., and Cole, M. W., 1998, Low Coverage Adsorption in cylindrical pores, Surf. Sci.

395:280.

*To whom correspondence should be addressed. Silvia Giordani, Molecular Electronics and

Nanotechnology Group, Physics Department, Trinity College, Dublin 2, Ireland; e-mail: giordans@tcd.ie

211

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 211–212.

EFFECT OF SOLVENT AND DISPERSANT ON THE BUNDLE

DISSOCIATION OF SINGLE-WALLED CARBON NANOTUBES

SILVIA GIORDANI,

SHANE D. BERGIN, ANNA DRURY,

ÉIMHÍN NÍ MHUIRCHEARTAIGH, JONATHAN N.

COLEMAN AND WERNER J. BLAU

Molecular Electronics and Nanotechnology Group, Physics

Department, Trinity College, Dublin 2, Ireland

Abstract. Single-wall carbon nanotubes (SWNT) are severely restricted in their

applications, as they exist in rope-like bundles. Recently, J. Coleman et al.

demonstrated a spectroscopic method to monitor bundle dissociation in low

concentration NT-polymer composites.

In this work we present the results we

obtained with 2,5-dioctyloxy-1,4-distyrylbenzene (pDSB), a short-chain

analogues of the well known PPV. We found a strong dependence of the

concentration at which individual SWNTs become stable with the nature of the

solvent.

Keywords: Single-wall carbon nanotubes; dispersion; de-bundling; fluorescence;

microscopy

pDSB was synthesised in the house. It is strongly fluorescent, displays

minimal self-aggregation and disperses SWNTs in the organic solvents. Stock

solutions of pDSB and of SWCNT were made in the different solvents, and

were subject to sonication. Two identical solutions of pDSB in each solvent

were made and pure HiPCO SWNTs were added to one solution. Each solution

was then diluted, serially, on the order of twenty times to give a broad range of

CNT concentrations (10

-2

–10

-8

kg/m

). Each solution was sonicated and then

allowed to stand for 24 hours to come to equilibrium. No sedimentation was

observed over this period. The absorption and emission spectra of each solution

were recorded. The addition of the SWNTs to the pDSB results in a visible

quenching of the emission, indicating interaction between the two. The

molecule exists in two forms, free and bound to the SWNT. The PL efficiency

for the bound form is expected to be extremely low as any photo-generated

212

singlet excitons preferentially decay non-radiatively through the fast vibrational

manifold of the nanotubes. Thus any observed PL from the composite solutions

is due to the free form only. For all concentrations, the fraction of free molecule

in each solvent was calculated from the PL intensity ratio of composite solution

to that of the pure molecule solution. Figure 1 reports the results obtained with

pDSB in three different solvents. The solid black lines represent the response of

an individual-SWNT system as deduced from Coleman’s model, fitted for the

results obtained in chloroform and in N-methyl-2-pyrrolidone (NMP). In the

case of the chlorinated solvent the experimental data deviates from this curve at

SWNT concentrations higher than 1 x 10

-7

kg/m

indicating that bundles occur

above this limit. In the case of the amide solvents the response does not deviate

from the solid curve, indicating that individual SWNTs or small bundles of

SWNTs are present up to the limit of the experiment. Preliminary AFM and

TEM results agreed with the spectroscopic results. There is a clear shift in the

bundle size distribution, to smaller bundles, in the amide solvent versus the

chlorinated solvent. The dominant feature is the presence of small SWNT

bundles at relatively high SWNT concentrations in the case of the amide

solvent.

Figure 1. Graph of the fraction of free molecules as a function of concentration for pDSB in the

different solvents.

References

1. J. N. Coleman, A. Fleming, S. Maier, S. O'Flaherty, A. Minett, M. S. Ferreira, S. Hutzler, W.

J. Blau,

Binding Kinetics and SWNT Bundle Dissociation in Low Concentration

Polymer – CNT Dispersions,

J. Phys. Chem. B 108, 3446-3450 (2004).

*To whom correspondence should be addressed. Ana Proykova; e-mail: anap@phys.uni-sofia.bg

213

V.N. Popov and P. Lambin (eds.), Carbon Nanotubes, 213–214.

CARBON NANOTUBES WITH VACANCIES UNDER EXTERNAL

MECHANICAL STRESS AND ELECTRIC FIELD

HRISTO ILIEV, ANA PROYKOVA*

Department of Atomic Physics, University of Sofia, Bulgaria

FENG-YIN LI

National Chung Hsing University, Taiwan

obtained with the CASTEP 4.2 code. Molecular Dynamics simulations show

that the vacancy distribution is important for the tube stability under stress.

Keywords: carbon nanotubes; defects; vacancies; electronic structure

The regular graphene structure that comprises carbon nanotubes (CNT)

determines their extraordinary mechanical and electronic properties. In the

presence of defects, the single-wall CNTs are less robust and their band

structure can be changed. Understanding the role of the defects on the CNT

properties is important for the development of CNT based nanodevices.

The structural defects in CNTs can roughly be divided into topological

defects and vacancies. We present a few results from Molecular Dynamics

(MD) simulations of CNTs with different distributions and amounts of

vacancies under an external load and a result from DFT calculations of the

band-structure of a single-wall (10, 0) CNT with ~ 1% vacancies.

Classical MD simulations with a velocity Verlet algorithm for integration of

the Newtonian equations of motion were performed to study defective CNTs

response to an external field. Details of the simulations were published in the

Ref. [1].

The simulations show that vacancies reduce the tensile strength of a

SWCNT depending on their distribution and concentration as it is shown in Fig.

1. It might happen that different amounts of vacancies could have the same

effect if they are properly distributed.

Abstract.. Reduction of the gap in a (10,0) carbon nanotube with vacancies is

214

0.0

5.0

10.0

15.0

20.0

Time [ps]

0.0

0.5

1.0

1.5

Strain energy [eV/atom]

10%

Figure 1. The strain energy per atom in a (10,0) SWCNT with 2000 atoms and various defect

concentrations (1%, 5% and 10%). For every concentration we present several curves

corresponding to different defect distributions generated randomly.

We have also demonstrated with DFT calculations (CASTEP code) that a

zigzag (10,0) SWNT with a mono-vacancy defect responds quite differently to

a transverse electric field applied in different directions. The defect site of the

defective nanotube provides a conducting band minimum with a lower energy

(0.19 eV) than in the corresponding perfect nanotube (0.4 eV). Our results

indicate that the band gap can be modulated by rotating a SWNT with a mono-

vacancy defect under a transverse electric field. Upon application of a strong

electric field, the band gap becomes similar to that found in the corresponding

perfect nanotubes. This also provides some flexibility to select a suitable band

gap for some specific applications because the band gap can increase or

decrease depending on the direction and strength of the transverse electric field.

References

1. Hristo Iliev and Ana Proykova, Mechanically induced defects in single-wall carbon

nanotubes, in: Meetings in Physics @ University of Sofia, edited by A. Proykova, vol. 5

(Heron Press, Sofia, 2004) pp. 87-91.

Part V. Mechanical properties of nanotubes

and composite materials