Marulanda J.M. (ed.) Electronic Properties of Carbon Nanotubes

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Preface XI

Chapter 9. Geometric and Spectroscopic Properties of Carbon Nanotubes and Boron Nitride

Nanotubes

In this chapter, the calculated Raman and IR spectra of functionalized (7,0)-SWCNT

are provided using the B3LYP functional with the basis sets 6-31G on carbon and

hydrogen atoms and 6-311G(d,p) basis set used for oxygen and nitrogen atoms.

Chapter 10. Detection of Carbon Nanotubes Using Tip-Enhanced Raman Spectroscopy

As a tip-enhanced spectroscopy, it is shown how TERS system combines SPM (STM,

AFM, SFM, SNOM) scanning head, Raman spectroscope, optical microscope, control

units and data acquirement into a complicated topography and spectral measuring

system.

Chapter 11. Spectro-Microscopic Study of Laser-Modified Carbon Nanotubes

In this chapter, a technique that facilitates exclusive chemical modification of the CNTs

with controlled locality using a focused laser beam is discussed. With focused laser

beam, a morphology modification and structural rearrangement of the CNTs are

achieved. With the CNTs housed in a transparent chamber with controlled gaseous

environment, we can select the appropriate gas species for the chemical modification

Chapter 12. Enhanced Control of Carbon Nanotube Properties Using MPCVD with DC

Electrical Bias

This chapter shows an examination of the role of dc electrical bias during microwave

plasma-enhanced chemical vapor deposition (MPCVD) synthesis of SWNTs using

alignment, spatial density, chirality, and purity as metrics of interest. Furthermore, it

is demonstrated that enhanced thermal and electrical transport properties of MWNTs

are realized with application of substrate bias during MPCVD synthesis.

Chapter 13. Spin Dependent Transport Through a Carbon Nanotube Quantum Dot in the

Kondo Regime

An impact of symmetry-breaking perturbations in CNTs in the Kondo regime on

transport is discussed. In specific this chapter focuses on the influence of magnetic

field and polarizations of electrodes. The conclusions drawn in this chapter can be

easily applied to the case of manipulating of orbital degrees of freedom (orbitronics) as

well.

Chapter 14. A Density Functional Theory Study of Chemical Functionalization of Carbon

Nanotubes; Toward Site Selective Functionalization

This chapter briefly presents how computational methods influence a description of its

CC bonding network. Results of mono or double functionalization of nanotubes are

given. In addition, the use of geometrical constraints of a bismalonate for site-selective

addition into a nanotube is shown.

Chapter 15. Low-Energy Irradiation Damage in Single-Wall Carbon Nanotubes

The low-energy irradiation damage and its defect characteristics are studied. The

damage and recovery are reversible, indicating that the number of carbon atoms is

XII Preface

preserved. The damage has been observed in SWCNTs, but not in multi-wall carbon

nanotubes (MWCNTs), suggesting that it is specific to low-dimensional structures or

nanostructures. The irradiation often converts the electric properties of a metallic

SWCNT into semiconducting, because the defect opens a local band gap in the metallic

SWCNT.

Chapter 16. Exciton Dephasing in a Single Carbon Nanotube Studied by Photoluminescence

Spectroscopy

In this chapter, the temperature and chirality dependence of the photoluminescence

(PL) line width of single carbon nanotubes using single SWNT spectroscopy is studied.

This is used to clarify the mechanism of exciton dephasing. The PL line width of a

single carbon nanotube broadened linearly with increasing temperature, indicating

that the line width and exciton dephasing are determined through exciton-phonon

interactions, is discribed.

Chapter 17. A Numerical Study of the Vibration Spectrum for a Double-Walled Carbon

Nanotube Model

This chapter presents numerical results for a double-walled carbon nanotube model

with non-conservative boundary conditions, given in the form of two Timoshenko

beams coupled through a distributed Van der Waals force.

Chapter 18. Electronic Band Structure of Carbon Nanotubes in Equilibrium and Non-

Equilibrium Regimes

In this chapter, the concept of chiral vector, chiral angle and the radius of SWCNTs are

first discussed and formulated. The authors then proceed to explaining how different

symmetries of single walled carbon nanotubes including translational, helical and

rotational symmetries affect the electronic band structure.

Chapter 19. An Alternative Approach to the Problem of CNT Electron Energy Band Structure

It is intended to discuss in this chapter, TBM (tight binding method), APW

(augmented-plane-wave), OPW (orthogonalized-plane-wave) methods and

corresponding theoretical concepts. In particularly, conventional band structure

models such as the nearly electron approximation (NFA), TBM, APW and OPW

models have been used for determining the electron energy band structure.

Chapter 20. Electronic Structure and Magnetic Properties of N@C

60-SWCNT

The design of spin labels for the NMR quantum computer that contained 1D spin

chains filling SWCNT with N@C60 is proposed. The electronic structure, chemical shift,

g-tensor, A-tensor of hfc is influenced by geometrical structure, varied with diameter

and chiral index.

Chapter 21. Carbon Nanotubes Addition Effects on MgB

2 Superconducting Properties

This chapter presents a review of recent developments in the study of the effect of

carbon nanotubes (CNT) on the superconducting properties of MgB

2 bulk and wire

samples, based on the known literature data and our own results.

Preface XIII

Chapter 22. Carbon Nanotube as VLSI Interconnect

An overview of the exploratory research on CNT as possible VLSI interconnect is

presented. The problem of continuing with copper interconnects in highly scaled

future technologies are briefly discussed. The work carried out in finding an

alternative solution indicates that the CNT based interconnects have the potential to

replace copper in future.

Chapter 23. Carbon Nanotube Based Magnetic Tunnel Junctions (MTJs) for Spintronics

Application

Spintronics devices are the next generation electronic devices with larger capacity and

minimum power consumption. After reviewing the basics of MTJs (from fabrication to

phenomena), the attention is directed to experimental results from the growth of

vertically aligned CNTs and the special methods of fabrication for CNT based

spintronics devices.

Chapter 24. Mechanisms of Single-Walled Carbon Nanotube Nucleation, Growth and

Chirality-Control: Insights from QM/MD Simulations

This chapter reviews recent investigations into the phenomena of SWNT nucleation

and growth using state-of-the-art QM/MD methods. The significance of the QM/MD

method in this context has therefore been demonstrated. QM/MD simulations of such

non-equilibrium, high-temperature processes can provide fundamental knowledge

that complements experimental understanding.

Chapter 25. Multiple Andreev Reflections and Enhanced Quantum Interferences in

NbN/Network-Like Carbon Nanotubes/NbN SNS Junctions

In this chapter, the superconducting proximity effect in S/network-like CNTs/S

junctions is observed in the correction of conductance and magneto conductance

fluctuations. Enhanced magneto conductance fluctuations similar to UCFs are

observed.

Chapter 26. Quantum Calculation in the Prediction of the Properties of Single-Walled Carbon

Nanotubes

This chapter discusses the calculation of the normal modes using the U Matrix. Ab

initio calculations are carried out with GAUSSIAN 98 program at the HF/3-21G level

of theory to investigate the effects of polar solvents and different temperatures on the

stability of SWCNT in various solvents. Quantum Mechanics (QM) are used to

investigate the nature of metals transport and the interaction with single-walled

carbon nanotubes (SWCNTs) inters membranes.

Chapter 27. Single Wall Carbon Nanotubes in the Presence of Vacancies and Related Energy

Gaps

This chapter studies the essential properties of carbon nanotubes, electronic density of

states, the coherent potential approximation and the existence of vacancies as they

generate the energy gap in carbon nanotubes.

XIV Preface

Chapter 28. STM Observation of Interference Patterns Near the Endcap and its Application to

the Chiral Vector Determination of Carbon Nanotubes

In this chapter, there is a discussion on the STM measurements focusing on the super

lattice structures detected near the endcap of the CNT. This is achieved by combining

high-resolution STM imaging and several types of simulation methods both for

metallic and semiconducting CNT.

Chapter 29. Liquid Crystal-Anisotropic Nanoparticles Mixtures

This chapter studies the impact of LC orientation ordering on alignment of carbon

nanotubes (CNTs). It comparatively presents the theoretical results obtained in the two

anchoring limits: i) the weak anchoring limit of the nematic liquid crystals molecules

at the nanotubes' surface, where the nanotubes alignments are caused by the

anisotropic interfacial tension of the nanotubes and ii) the strong anchoring limit for

which the nematic ordering around nanotubes is apparently distorted (consequently,

relatively strong long-range and anisotropic interactions can emerge within the

system).

Chapter 30. Strategies to Successfully Cross-Link Carbon Nanotubes

In this chapter, there is a review on some of the successful approaches used to cross-

link CNTs with a focus on the importance of the chemistry and techniques involved.

This chapter shows how, during cross-linking of carbon nanotubes, the formation of

highly cross-linked CNT composites, the de-fluorination process is clearly an

advantage.

Acknowledgments

I would like to thank the authors of the chapters for their excellent contributions in

their areas of expertise and for the efforts invested in the publication of their work. I

am certainly sure that the material published in this book will be of a great help and

genuinely appreciated by students, professors, and researchers all around the world.

Jose Mauricio Marulanda

Part 1

Synthesis of Carbon Nanotubes

Assembly of Carbon Nanotube Sheets

Mei Zhang

and Ray Baughman

Florida State University

University of Texas at Dallas

The United State of America

1. Introduction

Over the past decades, carbon nanotubes (CNTs) have been actively explored as building

blocks for next-generation electronics (Tans et al., 1998; Bachtold et al., 2001; Misewich et al.,

2003), optoelectronics, and sensors (Kong et al., 2000; Xia et al., 2003; T. Zhang, 2008),

including flexible and transparent devices ( Ju et al., 2007) as well as stretchable devices (Xu

et al., 2011). A critical step in constructing CNT-based devices is assembly of CNTs on a

substrate or free-standing for device fabrication, which include alignment, density control,

and transfer. Scalable and controlled assembly of CNTs synthesized with diverse methods

(e.g., solution fabrication or solid-state fabrication methods) on diverse substrates (e.g.,

silicon, plastics, rubbers, etc) or free-standing presents a major fabrication challenge that

must be overcome if CNTs are to be utilized in practical applications. For assembling CNTs

into thin films (or called sheet, buckypaper), there are several different methods or processes

in different conditions (e.g., solution or solid-state processes) (Hu et al., 2010). Solution

processes start with the CNTs in powder form; the powder is dispersed in an appropriate

solvent with or without functionalization. The CNT films (buckypapers) are usually made

using versions of the ancient art of paper making, by typically long-time filtration of

nanotubes dispersed in solvent and peeling the dried nanotubes as a layer from the filter

(Rinzler et al., 1998; Endo et al., 2005). Buckypaper normally has a laminar structure with a

random orientation of the bundles of the nanotubes in the plane of the film (Berhan et al.,

2004). Interesting variations of the filtration route provide ultra-thin nanotube sheets that

are highly transparent and highly conductive (Wu et al., 2004; Hu et al., 2004). While

filtration-produced sheets are normally isotropic within the sheet plane, sheets having

partial nanotube alignment result from applying high magnetic fields during filtration

(Fischer et al., 2003). In other important advances, nanotube films have been fabricated by

Langmuir-Blodgett deposition (Y. Kim et al., 2003), casting from oleum (Sreekumar et al.,

2003), coating (Ago et al., 1999; Dan et al., 2009), and printing (Zhou et al., 2006; Unidym Inc,

2007). The solid-state processes generally have two approaches. One is to synthesize CNTs

by floating catalyst chemical vapor deposition (CVD), either to deposit CNTs on a substrate

inside the CVD chamber or to collect the CNT aerogel outside of the chamber on a special

substrate and then densify it into a film (Y. Li et al., 2004; Martin, 2010). The catalysts are

with the CNTs and the CNTs in the film are usually disoriented. The optimized process

control lowers the impurities to less than 5 wt% in the film and a 1.2 meter wide and 10

meter long CNT film has been made (Nanocomp Tech. 2010). The other approach is to

Electronic Properties of Carbon Nanotubes

synthesize CNTs from the catalysts fixed on substrate to form a array either parallel to the

substrate (Kong et al., 1998) or perpendicular to the substrate (also called vertical aligned

CNT forest) which are fabricated into the CNT films after the synthesis process by the

“domino pushing effect” motion (Ding et al., 2008; Pevzner et al., 2010) or drawing CNTs

out of the forest (M. Zhang et al., 2004 & 2005). The domino pushing of the CNT forest can

efficiently ensure that most of the CNTs are aligned tightly in the film. Well aligned CNT

sheets are obtained by drawing CNTs from the forest.

For fabricating sheets that have close to single nanotube properties, long nanotubes are

needed. Solution fabrication methods work only for short nanotubes since the ability to

disperse nanotubes into a liquid and to fabricate oriented nanotube sheets from liquid

dispersions decreases with increasing nanofiber length. Solid-state fabrication methods do

not disturb the length of the nanotubes and are the methods that benefit from long

nanotubes. In this chapter, two processes for assembling well aligned and super-thin CNT

sheets are presented. One is to produce a drawable CNT forest, which has special topology,

by CVD and then draw CNTs out of forest to form a free-standing CNT sheet. Another

process involves synthesis of a patterned CNT array on substrate by CVD and then

knocking them down to form an aligned CNT sheet on substrate with the help of the

solvent. The CNT growth and the conditions for making drawable CNT forests are

discussed.

2. Fabrication of CNT sheet

Since the CNT sheets are fabricated directly from the forests, the synthesis of the CNT forest

is an important step. In this chapter, the CNTs are multi-walled CNTs. The CNT forests

were synthesized by catalytic CVD using hydrocarbon gas, acetylene or ethylene, as the

carbon source (M. Zhang et al., 2004). The following is the basic process and conditions. The

catalyst was a ~3 nm thick iron film, which was deposited on a silicon substrate by electron

beam evaporation. The substrates were set in the center of a quartz tube furnace. After

heating up to 680°C in helium at one atmospheric pressure, 5 molar percent acetylene in

helium was introduced at the total flow rate of 580 sccm. Within a few minutes, the dense

and vertically aligned CNT forests were grown on substrates. After removing the forest, the

substrate is still catalytically active and can be used to grow new forest, indicating a root-

growth mode and the presence of the catalysts on the substrate. Based on scanning electron

microscopy (SEM), transmission electron microscopy (TEM), and thermo-gravimetric

analysis (TGA), the purity of the nanotube forests was very high ( more than 99% carbon in

the form of CNTs), with less than 1 wt% iron and amorphous carbon, but more importantly,

no carbon particles within the CNTs were observed. The CNT sheets are made from the

CNT forests by two approaches, knocking down and drawing.

2.1 Knocking down approach

The schematic of the knocking down approach is shown in Fig. 1. The line arrays of thin Fe

film was made by patterning the resist on Si substrate following the standard lithography

process, depositing the catalyst thin film by electron beam evaporation and then the lifting

off the resist mask. The Fe film cracked into nanoparticles as catalysts for CNT growth

during the temperature ramp up in CVD process. The CNTs grew away from the catalyst

particles and formed a thin wall array during the CVD process (Figs. 2a to 2c). The CNT

wall is very thin, so it is transparent (Fig. 2a). The substrate with the array of CNT walls was