Background about Carbon Nanotubes

CAR Seminar5 November 2010

Meg Noah

Carbon Nanotubes (CNT) A rolled up graphene sheet Unique physical & chemical

properties flexibility extremely strong, about 100

times stronger (stress resistant) than steel

light-weight 1/6th the weight of steel

either conductors or semiconductors

intrinsic superconductivity (ballistic electron transport)

ideal thermal conductors field emitters

MAN 10Aug07

SWNT and MWNT

• Single Wall NanotubeDiameters 0.6-1.8 nm (1.4 nm is typical)

Elastic Modulus 1210 GPa

Strain 4%

Density 1.4 g/cm3

• Multi Wall NanotubeDiameters 20 - 50 nm

Elastic Modulus 1260 GPa

Strain 1.5%

Density 1.8 g/cm3

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Chirality

1a

2a

1 2Chirality Vector na ma

1 25 0

(5,0)hC a a

Zigzag

1 23 3

(3,3)hC a a

Armchair

1 21 3

(1,3)hC a a

Chiral

MAN 10Aug07

Chirality and Structural Properties

MAN 10Aug07

The hexagonal lattice vectors:

For graphite aC-C= 1.421 Å is the bond distance. For CNT it is about 1.44 Å and depends on radius.

SWNT Circumference from Chirality indices (n,m):

The Diameter of the SWNT:

2 23h C CC ad n nm m

1 2

2 2

Chirality Vector

3

h

h C C

C na ma

C a n nm m

3 33 31 22 2 2 2, ,C C C C C C C Ca a a a a a

1a

2a

Chirality and Electrical Properties

Armchair (n=m)All metallicNone semiconducting

Chiral (n ≠ m)1/3 are metallic2/3 are semiconductingmetallic when (n-m)=3*integer

ZigZag (m=0)1/3 are metallic2/3 are semiconductingmetallic when n=3*integer

Example: (5,5) 200 atoms Diameter = 6.78 ÅLength = 24.60 Å

Example: (5,0) 200 atomsDiameter = 3.91 ÅLength = 42.60 Å

Example, (5,3) 196 atomsDiameter = 5.48 ÅLength = 29.82 Å

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Chirality – Unique ID (n,m)

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The Chirality Vector indices (n,m) uniquely define the SWNT: Diameter Electronic Properties (metallic, insulating,

semiconducting) To know the diameter of a SWNT is to know the

chirality indices (n,m), and thus it’s structural, electronic and mechanical properties.

Images are from:

http://www.blog.speculist.com/archives/000193.htmlhttp://www.swissvalley.com.sg/07bmc_slc01.htmhttp://www.t3.co.uk/news/247/general/general/bendable_computer_screens_roll_into_action

http://www.computerpoweruser.com/Editorial/article.asp?article=articles/archive/c0209/60c09/60c09.asp&guid=

Applications of CNT

1: Tethering cable for he space elevator

2: Low power flexible displays

3: Light weight Bicycle frames

4: Transistors for future central processing unit (CPU)

12

3

4

SEM Images from NEU

• From the lower magnification (~200X to ~1000X) the CNT length is measured.

SEM Images from NEU• Used to visually assess the quality of CNT.

Can we develop an automated algorithm for determining quality? Is quality correlated to processing parameters?

13 s10 mA200 sccm

Cobalt Sputter Time: 13 sCobalt Sputter Current: 5 mAEthanol Gas Flow Rate: 200 sccm

Bad Results Good Results