CARBON NANOTUBES (CNT):

PROPERTIES AND APPLICATIONS

Prof. Anurag Srivastava

Content

Introduction

History

Structure of CNT and its properties

Synthesis and purification method

Types of CNT

Applications and benefits

Carbon allotropes

Carbon is capable of forming many allotropes due

to its valency. Various allotropes of carbon exhibits

different properties and find application in variety

of fields.

Diamond

Graphite: Graphene

Fullerenes: CNT, Buckyball, Nanobuds

Carbon NanoTube

A CNT is a graphene sheet (with carbon atoms appearing in ahexagonal pattern) rolled up to form a hollow cylinder.

CNTs are members of the fullerene structural family.

They have extremely low electrical resistance because of whichelectrons can travel for larger distances without scattering.

This is partly due to their very small diameter and huge ratio oflength to diameter. Also, because of their low resistance, CNTsdissipate very little energy.

History of CNT

Structure of CNTs

To understand the atomic structure of CNTs, one can imagine

taking the structure of graphite

•Graphene is pure carbon in

the form of a very thin, nearly

transparent sheet, one atom

thick.

•It is remarkably strong for its

very low weight (100 times

stronger than steel) and it

conducts heat and electricity

with great efficiency.

A CNT can be viewed as a rolled-up graphene strip

which forms a closed cylinder

Contd…

where a = 0.142 nm is the carbon–carbon bond length.

C = na1 + ma2

C=Circumferential vector

A,B= 2 atoms in unit cell of graphene

Electronic properties

Zigzag : n or m=0, θ= 00

ARM Chair : n =m, θ= 300

Carbon nanotube can be metallic or semiconducting

based on the following rule

n - m = 3i ⇒ Metallic

n – m! = 3i ⇒ Semiconducting

Where; i is an integer

A small increase in diameter has a major impact on

the conduction properties of carbon nanotubes.

Comparison: Graphene Nanoribbon (GNR) Vs CNT

Hamada Indices

(n,m)GNR CNT

n=m Zig-Zag Arm-Chair

n/m=0 Arm-Chair Zig-Zag

GNR CNT

Zig-Zag Metallic SC/Metallic

Arm-Chair SC/Metallic Metallic

Reason for this variation Shape

of scattering region

Band Gaps & Fermi Level of Materials

A. Conductor B. Semiconductor C. Semimetal

Band structure of CNTs

a. Armchair (5,5) Nanotube

b. Zigzag (9,0) Nanotube

c. Zigzag (10,0) Nanotube

Types of CNT

1. Based on Structure

Single Walled NanoTube (A one atom thick layer of graphene into

seamless cylinder)

• Diameter= 1-2 nm; Band gap= 0-2 eV

Multi Walled NanoTube

• Diameter= 2-25 nm , Interlayer distance= 3-4 Å

2. Based on conductivity

Metallic CNT

• Usage: As an interconnects in both silicon nanoelectronics andmolecular electronics because of their low resistance and strongmechanical properties.

Semiconducting CNT

• Usage: As channel material in semiconductor applications eg. Transistors, Electronic design and design automation. etc.

Material Thermal conductivity (W/m-K) Electrical conductivity (S/m)

Carbon Nanotube > 3000 106 – 107

Copper ~400 6 x 107

Gold ~350 4.10 x 107

Silver ~420 6.3 x 107

Production of CNT

Synthesis

1. ARC-discharge method 2. Chemical vapor deposition (CVD)

3. Laser Abletion

(Vaporization)

Purification

Oxidation: Removes carbonaceous impurities

Acid treatment: Removes metal catalyst

Annealing: Rearranges the defects

Ultrasonication: Separation of nanoparticles

Magnetic purification: ferromagnetic impurity

Microfilteration: size or particle separation

Cutting: Cuts the length

Functionalization

Chromatography

Properties of CNT

Small size

Exceptional electrical properties(Ballistic transport)

Large current carrying capability

High mobility

CNT Applications

CNTs Thermal Conductivity (as an interconnect, coolants etc.)

CNTs Field Emission

CNTs Conductive Properties

CNTs Energy Storage (as an electrode materials, supercapacitors etc.)

CNTs Conductive Adhesive

Molecular Electronics based on CNTs

CNTs Thermal Materials

CNTs Structural Applications

CNTs Fibers & Fabrics

CNTs Catalyst Supports

CNTs Biomedical Applications

CNTs Air & Water Filtration

Other CNT Applications

Benefits of CNT devices

Predictable electron transport properties

Reliable device performance

Unique properties due to quantum confinement effects

Enhancement in device characteristics

Potential to revolutionize nano-scale science and technology