Carbon Nanotubes CARBON NANOTUBES - PowerPoint Presentation

Slide1

Carbon NanotubesSlide2

CARBON NANOTUBES

Discovered in 1991 by

Sumiyo

Iijima

, a Japanese scientist working at the NEC Corporation.

Is a tubular form of carbon with a diameter as small as 0.4 nm and length from a few nanometers up to a millimeter. 

Length-to-diameter ratio of a carbon nanotube can be as large as 28,000,000:1, which is unequalled by any other material.

Carbon exists in several forms; graphite and diamond are the most familiar.

A CNT is characterized by its

Chiral

Vector:

C

h

= n

â

1

+ m

â

2

,

Slide3

Formation of CNT

Process which is used to form these Nanotubes, is called

Chemical Vapor Deposition

.

Can be made in a standard chemistry laboratory.

A quartz tube about 1 inch in diameter serves as the growth reactor and is inserted inside a tube furnace.

Scanning electron microscopy of nanofibers covered with nanotubesSlide4

Tube furnace is a standard heating device for conducting, syntheses and purifications.

Nanotube grows on a silicon wafer that is placed at a central location inside the quartz tube.

A thin layer of iron or nickel or cobalt is applied to the silicon wafer to serve as a catalyst to grow the nanotubes.

In a few minutes, the silicon wafer appears black, indicating that it is covered with nanotubes.Slide5

Types of CNTs

Single Wall CNT (SWCNT)

Multiple Wall CNT (MWCNT)

Can be metallic or semiconducting depending on their geometry.Slide6

Single Walled CNT’s

Made by  a single layer of a graphite sheet, cutting it into a small piece of any size, and rolling it.

Single-walled carbon nanotubesSlide7

SWCNT….

Characterized by a set of two integers (n, m) called the 

Chirality

vector.

When (n-m)/3 is an integer (for example when n is 8 and m is 2), then the nanotube has metallic properties.

If (n-m)/3 is not an integer, the corresponding nanotube behaves like it is a semiconductor.Ability to create tubes of either metallic or semiconductor nature is of great practical importance.Slide8

Conti..

Single wall carbon nanotubes exhibit extraordinary mechanical properties.

Hundred times stronger than steel at one-sixth of its weight.

Ability to carry current and heat along the axial direction is extraordinary.

Has the potential to replace copper wires as conductors.

Scientists and engineers envision all carbon-based electronics using semiconducting and metallic carbon nanotubes of different values of n and m. Slide9

Types of Single-Walled Carbon Nanotubes

n

and

m

can be counted at the end of the tube

Zigzag (

n

,0)Slide10

Types of Single-Walled Carbon Nanotubes

Chiral

(

n

,

m

)

Armchair (

n

,

n

)Slide11

Armchair (

n,m

) = (5,5)

 = 30

Zig

Zag

(

n,m

) = (9,0)

 = 0

Chiral

(

n,m

) = (10,5)

0 < < 30Slide12

MWCNT

A tower of

multiwalled

carbon NanotubesSlide13

Take multiple layers of a graphite sheet and roll them in the form of a cylinder.Slide14

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Fig. 2. (a).

Band structure of a

graphene

sheet (top) and the first

Brillouin zone (bottom).

(b) Band structure of a metallic (3,3) CNT. (c)

Band structure of a (4,2) semiconducting CNT. The allowed states in the nanotubes are cuts of the

graphene

bands indicated by the white lines. If the cut passes through a K point, the CNT is metallic; otherwise, the CNT is semiconducting.Slide18

CNT PropertiesSlide19

CNT Properties (cont.)Slide20

Nanotubes Growth Methods

a) Arc Discharge b) Laser

Abalation

Involves condensation of C-atoms generated from evaporation of solid carbon sources. Temperature ~ 3000-4000K, close to melting point of graphite.

Both produce high-quality SWNTs and MWNTs.

MWNT: 10’s of m long, very straight & have 5-30nm diameter. SWNT: needs metal catalyst (Ni,Co etc.). Produced in form of ropes consisting of 10’s of individual nanotubes close packed in hexagonal crystals. Slide21

Nanotubes Growth Methods

c) Chemical Vapor Deposition:

Hydrocarbon + Fe/Co/Ni catalyst

550-750

°

C CNTSteps:

Dissociation of hydrocarbon. Dissolution and saturation of C atoms in metal

nanoparticle

.

Precipitation of Carbon.

Choice of catalyst material?

Base Growth Mode or Tip Growth Mode?

Metal support interactionsSlide22

Application

Electrical

Field emission in vacuum electronics

Building block for next generation of VLSI

Nano lithography

Energy storage

Lithium batteries

Hydrogen storage

Biological

Bio-sensors

Functional AFM tips

DNA sequencingSlide23

Challenges & Future..

Future applications:

Already in product: CNT tipped AFM

Big hit: CNT field effect transistors based

nano

electronics.Futuristic: CNT based OLED, artificial muscles…

Challenges:Manufacture: Important parameters are hard to control.

Large quantity fabrication process still missing.

Manipulation of nanotubes.Slide24

Conclusion

Their phenomenal mechanical properties, and unique electronic properties make them both interesting as well as potentially useful in future technologies.

Significant improvement over current state of electronics can be achieved if controllable growth is achieved.

Growth conditions play a significant role in deciding the electronic and mechanical properties of CNTs.

Growth Mechanisms yet to be fully established.Slide25

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