Carbon Nanotubes Episode 1 pdf

SARKAR: Pyrolytic carbon nanotubes from vapor-grown carbon fibers... X Preface From an experimental point of view, definitive measurements on the properties of individual carbon nanotub

CARBON NANOTUBES

Elsevier Journals of Related Interest

Applied Superconductivity

Carbon

Journal of Physics and Chemistry of Solids Nanostructured Materials

Polyhedron

Solid State Communications

Tetrahedron

Tetrahedron Letters

CARBON NANOTUBES

Edited by

MORINUBO END0

Shinshu University, Japan

SUM10 IIJIMA

NEC, Japan

MILDRED S DRESSELHAUS

Massachusetts Institute of Technology, USA

PERGAMON

U.K Elsevier Science Ltd, The Boulevard, Langford Lane,

Kidlington, Oxford OX5 lGB, U.K

U.S.A Elsevier Science Inc., 660 White Plains Road, Tarrytown,

New York 10591-5153, U.S.A

Elsevier Science Japan, Tsunashima Building Annex, 3-20-12 Yushima Bunko-ku, Tokyo 113, Japan JAPAN

Copyright 0 1996 Elsevier Science Limited

All Rights Reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publisher

First edition 1996

Library of Congress Cataloging in Pulication Data

A catalog record for this book is available from the Library of Congress

British Library Cataloguing in Publication Data

A catalogue record for this book is available in the British Library

ISBN 008 0426824

Reprinted from:

Carbon, Vol 33, Nos 1, 2, 7, 12

Printed and bound in Great Britain by BPC Wheatons Ltd, Exeter

CONTENTS

M ENDO, S IIJIMA and M S DRESSELHAUS: Editorial ,

M S DRESSELHAUS: Preface: Carbon nanotubes , ,

M ENDO, K TAKEUCHI, K KOBORI, K TAKAHASHI, H W KROTO and

A SARKAR: Pyrolytic carbon nanotubes from vapor-grown carbon fibers

D T COLBERT and R E SMALLEY: Electric effects in nanotube growth *

V IVANOY, A FONSECA, J B NAGY, A LUCAS, P LAMBIN, D BERNAERTS and

X B ZHANG: Catalytic production and purification of nanotubes having fullerene- scale diameters

M S DRESSELHAUS, G DRESSELHAUS and R SAITO: Physics of carbon nanotubes

J W MINTMIRE and C T WHITE: Electronic and structural properties of carbon nanotubes

C.-H KIANG, W A GODDARD 111, R BEYERS and D S BETHUNE: Carbon nanotubes with single-layer walls ,

R SETTON: Carbon nanotubes: I Geometrical considerations

K SATTLER: Scanning tunneling microscopy of carbon nanotubes and nanocones

T W EBBESEN and T TAKADA: Topological and SP3 defect structures in nanotubes

S IHARA and S ITOH: Helically coiled and torodial cage forms of graphitic carbon

A FONSECA, K HERNADI, J B NAGY, P H LAMBIN and A A LUCAS: Model structure of perfectly graphitizable coiled carbon nanotubes

A SARKAR, H W KROTO and M ENDO: Hemi-toroidal networks in pyrolytic carbon

nanotubes ,

X K WANG, X W LIN, S N SONG, V P DRAVID, J B KETTERSON and

R P H CHANG: Properties of buckytubes and derivatives J.-P ISSI, L LANGER, J HEREMANS and C H OLK: Electronic properties of carbon nanotubes: Experimental results , ,

P C EKLUND, J M HOLDEN and R A JISHI: Vibrational modes of carbon nanotubes: Spectroscopy and theory

R S RUOFF and D C KORENTS: Mechanical and thermal properties of carbon

nanotubes

J IF DESPRES, E DAGUERRE and K LAFDI: Flexibility of graphene layers in carbon nanotubes

vii

ix

1

11

15

27

37

47

59

65

71

77

87

105

111

121

129

143

1.49

Y SAITO: Nanoparticles and filled nanocapsules 153

D UGARTE: Onion-like graphitic particles 163

U ZIMMERMAN N MALINOWSKI A BURKHARDT and T P MARTIN: Metal- coated fullerenes 169 Subject Index 181

vi

X Preface

From an experimental point of view, definitive

measurements on the properties of individual carbon

nanotubes, characterized with regard to diameter and

chiral angle, have proven to be very difficult to carry

out Thus, most of the experimental data available

thus far relate to multi-wall carbon nanotubes and to

bundles of nanotubes Thus, limited experimental

information is available regarding quantum effects

for carbon nanotubes in the one-dimensional limit

A review of structural, transport, and susceptibility

measurements on carbon nanotubes and related

materials is given by Wang et al., where the inter-

relation between structure and properties is empha-

sized Special attention is drawn in the article by

Issi et al to quantum effects in carbon nanotubes, as

observed in scanning tunneling spectroscopy, trans-

port studies and magnetic susceptibility measure-

ments The vibrational modes of carbon nanotubes

is reviewed in the article by Eklund et al from both

a theoretical standpoint and a summary of spec-

troscopy studies, while the mechanical that thermal

properties of carbon nanotubes are reviewed in the

article by Ruoff and Lorents The brief report by

Despres et al provides further evidence for the

flexibility of graphene layers in carbon nanotubes

The final section of the volume contains three complementary review articles on carbon nano- particles The first by Y Saito reviews the state of

knowledge about carbon cages encapsulating metal and carbide phases The structure of onion-like graphite particles, the spherical analog of the cylin- drical carbon nanotubes, is reviewed by D Ugarte, the dominant researcher in this area The volume concludes with a review of metal-coated fullerenes by

T P Martin and co-workers, who pioneered studies

on this topic

The guest editors have assembled an excellent set

of reviews and research articles covering all aspects of the field of carbon nanotubes The reviews are pre- sented in a clear and concise form by many of the leading researchers in the field It is hoped that this collection of review articles provides a convenient reference for the present status of research on carbon nanotubes, and serves to stimulate future work in the field

M S DRESSELHAUS REFERENCES

1 H W Kroto, Carbon 30, 1139 (1992)

2 S Iijima, Nature (London) 354, 56 (1991)

2 M ENDO et al

Fig 1 Comparative preparation methods for micrometer

size fibrous carbon and carbon nanotubes as one-dimensional

forms of carbon

methods give similar structures, in which ultra-fine

catalytic particles are encapsulated in the tubule tips

(Fig 2) Continued pyrolytic deposition occurs o n the

initially formed thin carbon fibers causing thickening

(ca 10 pm diameter, Fig 3a) Substrate catalyzed fi-

bers tend t o be thicker and the floating technique pro-

duces thinner fibers (ca 1 pm diameter) This is due

t o the shorter reaction time that occurs in the fluid-

ized method (Fig 3b) Later floating catalytic meth-

ods are useful for large-scale fiber production and,

thus, VGCFs should offer a most cost-effective means

of producing discontinuous carbon fibers These

VGCFs offer great promise as valuable functional car-

bon filler materials and should also be useful in car-

bon fiber-reinforced plastic (CFRP) production As

seen in Fig 3b even in the “as-grown” state, carbon

particles are eliminated by controlling the reaction

conditions This promises the possibility of producing

pure ACNTs without the need for separating spheroidal

carbon particles Hitherto, large amounts of carbon

particles have always been a byproduct of nanotube

production and, so far, they have only been eliminated

by selective oxidation[l4] This has led t o the loss of

significant amounts of nanotubes - ca 99%

Fig 2 Vapour-grown carbon fiber showing relatively early

stage of growth; a t the tip the seeded Fe catalytic particle is

encapsulated

Fig 3 Vapor-grown carbon fibers obtained by substrate

method with diameter ca 10 pm (a) and those by floating cat- alyst method (b) (inserted, low magnification)

3 PREPARATION OF VGCFs AND PCNTs

The PCNTs in this study were prepared using the same apparatus[9] as that employed to produce VGCFs by the substrate method[l0,15] Benzene va- por was introduced, together with hydrogen, into a ce- ramic reaction tube in which the substrate consisted

of a centrally placed artificial graphite rod The tem- perature of the furnace was maintained in the 1000°C range The partial pressure of benzene was adjusted

t o be much lower than that generally used for the preparation of VGCFs[lO,lS] and, after one hour decomposition, the furnace was allowed t o attain room temperature and the hydrogen was replaced by argon After taking out the substrate, its surface was scratched with a toothpick t o collect the minute fibers Subsequently, the nanotubes and nanoscale fibers were heat treated in a carbon resistance furnace un- der argon a t temperatures in the range 2500-3000°C for ca 10-15 minutes These as-grown and sequen- tially heat-treated PCNTs were set on an electron mi- croscope grid for observation directly by HRTEM at 400kV acceleration voltage

It has been observed that occasionally nanometer scale VGCFs and PCNTs coexist during the early stages of VGCF processing (Fig 4) The former tend

to have rather large hollow cores, thick tube walls and well-organized graphite layers On the other hand,

Pyrolytic carbon nanotubes from vapor-grown carbon fibers 3

a t

b

Fig 4 Coexisting vapour-grown carbon fiber, with thicker

diameter and hollow core, and carbon nanotubes, with thin-

ner hollow core, (as-grown samples)

PCNTs tend to have very thin walls consisting of only

a few graphitic cylinders Some sections of the outer

surfaces of the thin PCNTs are bare, whereas other

sections are covered with amorphous carbon depos-

its (as is arrowed region in Fig 4a) TEM images of

the tips of the PCNTs show no evidence of electron

beam opaque metal particles as is generally observed

for VGCF tips[lO,l5] The large size of the cores and

the presence of opaque particles at the tip of VGCFs

suggests possible differences between the growth

mechanism for PCNTs and standard VGCFs[7-91

The yield of PCNTs increases as the temperature and

the benzene partial pressure are reduced below the op-

timum for VGCF production (i.e., temperature ca

1000°-11500C) The latter conditions could be effec-

tive in the prevention or the minimization of carbon

deposition on the primary formed nanotubules

4 STRUCTURES OF PCNTs

Part of a typical PCNT (ca 2.4 nm diameter) af-

ter heat treatment at 2800°C for 15 minutes is shown

in Fig 5 It consists of a long concentric graphite tube

with interlayer spacings ca 0.34 nm-very similar in

morphology to ACNTs[ 1,3] These tubes may be very

long, as long as 100 nm or more It would, thus, ap-

pear that PCNTs, after heat treatment at high temper-

atures, become graphitic nanotubes similar to ACNTs

The heat treatment has the effect of crystallizing the

secondary deposited layers, which are usually com-

posed of rather poorly organized turbostratic carbon

Fig 5 Heat-treated pyrolytic carbon nanotube and enlarged one (inserted), without deposited carbon

This results in well-organized multi-walled concentric graphite tubules The interlayer spacing (0.34 nm) is slightly wider on average than in the case of thick VGCFs treated at similar temperatures This small in- crease might be due to the high degree of curvature of the narrow diameter nanotubes which appears to pre- vent perfect 3-dimensional stacking of the graphitic layers[ 16,171 PCNTs and VGCFs are distinguishable

by the sizes of the well-graphitized domains; cross- sections indicate that the former are characterized by single domains, whereas the latter tend to exhibit mul- tiple domain areas that are small relative to this cross- sectional area However, the innermost part of some VGCFs (e.g., the example shown in Fig 5 ) may often consist of a few well-structured concentric nanotubes Theoretical studies suggest that this “single grain” as- pect of the cross-sections of nanotubes might give rise

to quantum effects Thus, if large scale real-space super-cell concepts are relevant, then Brillouin zone- foiding techniques may be applied to the description

of dispersion relations for electron and phonon dy- namics in these pseudo one-dimensional systems

A primary nanotube at a very early stage of thick- ening by pyrolytic carbon deposition is depicted in Figs 6a-c; these samples were: (a) as-grown and (b), (c) heat treated at 2500°C The pyrolytic coatings shown are characteristic features of PCNTs produced

by the present method The deposition of extra car- bon layers appears to occur more or less simultane- ously with nanotube longitudinal growth, resulting in spindle-shaped morphologies Extended periods of py- rolysis result in tubes that can attain diameters in the micron range (e.g., similar to conventional (thick) VGCFs[lO] Fig 6c depicts a 002 dark-field image, showing the highly ordered central core and the outer inhomogeneously deposited polycrystalline material (bright spots) It is worthwhile to note that even the very thin walls consisting of several layers are thick enough to register 002 diffraction images though they are weaker than images from deposited crystallites on the tube

Fig 7a,b depicts PCNTs with relatively large diam- eters (ca 10 nm) that appear to be sufficiently tough