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