nano tube geometry1

SANDIP BHATTACHARYARAJKAMAL GHOSHRAJAT SUBHRA KARMAKARSOURAV ROY

TOPIC OF DISCUSSION

• BACKGROUND• HISTORY• INTRODUCTION TO CNT• WHY CNT(PROS & CONS)• DIFFERENT STRUCTURE OF

CNT• CNT GEOMETRY:CHIRAL

VECTOR• WRAPPING OF CNT• CONCLUSION

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BACKGROUND

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Courtesy To: Tom Grace; [email protected]

HISTORY• Before 1980 Carbon has 2 allotropes

– Diamond– Graphite

• 1985 : Richard E Smaley and others

discovered 60 carbon molecules

arranged in a typical structure while

working Graphite.• 1991: Sumio Iijima discovered fullerene

related carbon nanotubes

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• The structure is a Soccer Ball like strucure of 32 faces.

• 12 faces are of PENTAGONAL patterns and 20 faces are of HEXAGONAL patterns.

• This structure is called BUCKYBALL structure after the name of famous architect Buckminister Fuller who designed the 1st GEODOME in “SPACESHIP EARTH” at EPICOT CENTER(DISNEY WORLD)

• When BUCKYBALL structure are converted into cylindrical tube like structure it is called BUCKYTUBE later known as CARBON NANO TUBE.


Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure.

Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than any other material.

These cylindrical carbon molecules have novel properties, making them potentially useful in many applications in nanotechnology, electronics, optics, and other fields of materials science, as well as potential uses in architectural fields.

They may also have applications in the construction of body armor.

They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors.

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Pros:◦ One of the stiffest and strongest fibres known.◦ Have remarkable electronic properties and many other

unique characteristics- Great potential for storage memory (116 Gb /cmGreat potential for storage memory (116 Gb /cm2 2 )) Small size offers faster switching speeds (100GHz ) and low power.Small size offers faster switching speeds (100GHz ) and low power. Easy to fabricate using standard semiconductor process.Easy to fabricate using standard semiconductor process. Nonvolatile nature: no need to refresh.Nonvolatile nature: no need to refresh. Faster than SRAM, denser than DRAM, cheaper than flash memory. Faster than SRAM, denser than DRAM, cheaper than flash memory. Have an almost unlimited life, resistant to radiation and magnetism—better than Have an almost unlimited life, resistant to radiation and magnetism—better than

hard drive. hard drive.

Cons:◦ Commercial applications have been rather slow to

develop,because of the high production costs of the best quality nanotubes.

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CARBON NANOTUBE STRUCTURECARBON NANOTUBE STRUCTURE

Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs.

The ends of a nanotube may be capped with a hemisphere of the buckyball structure.

Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 1/50,000th of the width of a human hair.

Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).

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NANOTUBE GEOMETRY

• Types of carbon nanotubes and related structures :

1.Single-walled2 Multi-walled3 Torus4 Nanobud5 Cup stacked carbon nanotub


SINGLE WALL CARBON NANO TUBE

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer.

The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder.

The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector.

The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene.

If m = 0, the nanotubes are called zigzag. If n = m, the nanotubes are called armchair. Otherwise, they are called chiral.

The diameter of a nanotube can be calculated from its (n,m) indices as follows- d=a/π*sqrt(n^2+n.m+m^2)a=0.246 nm


PROPERTIES OF SWNT

• Band gap can vary from zero to about 2 eV .• Electrical conductivity can show metallic or

semiconducting behavior.• SWNT are the most likely candidate for

miniaturizing electronics currently used in electronics.

• The most basic building block of these systems is the electric wire, as SWNTs can be excellent conductors.


APPLICATION OF SWNT

• Most popular application ->Intramolecular Logic gates.• Logic gates are formed using SWNT-FET.

• SWNT-FET

• p-FET: While SWNT is Exposed to Oxygen.• n_-FET: While SWNT is not Exposed to Oxygen.• Inverter Logic->

– Both n-FET & p-FET on same molecule– Exposing half of SWNT to Oxygen by protecting other half to be

exposed.


p-FET

n-FET

•Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite.•There are two models which can be used to describe the structures of multi-walled nanotubes

Russian Doll model. Parchment model.

•MWNTs are zero-gap metals as Band Gap=0eV•The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å.

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•In the Russian Doll model, sheets of graphite are arranged in concentric cylinders.

In the Parchment model, a single sheet of graphite is rolled in

around itself, resembling a scroll of parchment or a rolled

newspaper

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Morphology and properties are similar to SWNT.

But resistance to chemicals is significantly improved.

This is especially important when Functionalization is required.

In the case of SWNT, covalent Functionalization will break some C=C double bonds, leaving "holes" in the structure on the nanotube and thus modifying both its mechanical and electrical properties.

In the case of DWNT, only the outer wall is modified.

DWNT synthesis on the gram-scale was first proposed in 2003 by the CCVD technique, from the selective reduction of oxide solutions in methane and hydrogen.


A. NANO TORUS STRUCTURE• A nanotorus is a carbon nanotube

bent into a torus (doughnut shape).

• Have many unique properties, such as larger magnetic moments , thermal stability, etc.

• Vary widely depending on radius of the torus and radius of the tube.

B. NANO BUDS STRUCTURE

•Carbon nanobuds are a newly created material combining two previously discovered allotropes of carbon: carbon nanotubes and fullerenes.

•In this new material, fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying carbon nanotube.

•This hybrid material has useful properties of both fullerenes and carbon nanotubes.

•In particular, they have been found to be exceptionally good field emitters.

C.CUP STACKED CARBON NANO TUBE

•Cup-stacked carbon nanotubes (CSCNTs) differ from other quasi-1D carbon structures, which normally behave as quasi-metallic conductors of electrons.

•CSCNTs exhibit semiconducting behaviors due to the stacking

microstructure of graphene layers.

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To describe the geometry of CNT we have to obtained the Cartesian Co-ordinates of an Atomic Sites of particular CN

Here we see how to find the co-ordinates of atomic sites of CNT with a specified CHIRAL VECTOR and specified number of UNIT CELLS.

CNT have special characteristics that made them special from electronic properties to mechanical properties.

It is a tiny tube made of carbon C60 atoms. It has a diameter in nanometer range and length in

micrometer range. One can imagine it as rolling of one graphitic sheet structure

into tube structure. The result is a tube consists carbon atoms on its surface

arranged in hexagonal patterns as shown below-

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TYPES OF NANO TUBE GEOMETRY 3 basic geometry-

Armchair(n ,n) Zig-Zag(n,0) Chiral(n,m)

These are also refered as Flavors. These Flavors can be classified by how the carbon sheet is wrapped

into a tube(see pictures below)

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CHIRAL VECTOR CONCEPTS The nanotube can be

conceptually viewed as a rolled-up graphene sheet.

The two-dimensional graphene lattice in real space can be created by translating one unit cell by the vectors-

Where R: Chiral Vectorm,n: Co-ordinate of atom

in atomic sitea1,a2: Basis Vector

R = na1 + ma2

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Chiral Angle: The angle between the Chiral vector R and the unit vector a1. Let denote it as θ

Now see how the geometry is defined with the help of Chiral vector from table below-

STM can determine the chirality of the structure and STM, AFM can determine the diameter

Armchair geometry shows metallic behavior

Zig-Zag geometry shows semiconducting behavior

The conductivity of CNT varies depending on the chirality n - m = 3q (q: integer): semiconductor. n - m 3q (q: integer): metallic.

Chiral Angle

Co-ordinate ‘n’

Co-ordinate ‘m’ Type of the Geometry

θ=0° Some Integer 0 Zig-Zag

θ=30° Some Integer Some Integer and m=n Armchair

0°<θ<30° Some Integer Some IntegerAnd may or may not

m=n

Chiral

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HEXAGONAL LATTICE (N,M) HEXAGONAL LATTICE (N,M) NANOTUBESNANOTUBES

a1

a2

x

y

(0,0) (1,0) (2,0) (3,0)

(1,1) (2,1)

Zigzag

Armchair

(2,2)

(4,0) (5,0) (6,0)

(3,1) (4,1) (5,1)

(3,2) (4,2) (5,2)

(7,0) (8,0) (9,0)

(6,1) (7,1) (8,1)

(6,2) (7,2) (8,2)

(10,0) (11,0)

(9,1) (10,1)

(9,2) (10,2)

(3,3) (4,3) (5,3) (6,3) (7,3) (8,3) (9,3)

(4,4) (5,4) (6,4) (7,4) (8,4) (9,4)

(5,5) (6,5) (7,5) (8,5)

(6,6) (7,6) (8,6)

(7,7)

n - m = 3q (q: integer):semiconductorn - m 3q (q: integer): metalic04/09/23 24


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(0,0)Ch = (10,0)

Wrapping (10,0) SWNT (zigzag)

a1a2

x

y

(0,0)Ch = (10,0)

Wrapping (10,0) SWNT (Animation)

a1a2

x

y

(0,0)

Ch = (10,10)

Wrapping (10,10) SWNT (armchair)

a1a2

x

y

(0,0)

Ch = (10,10)


a1a2

x

y

(0,0)

Ch = (10,5)

Wrapping (10,5) SWNT (chiral)

a1a2

x

y

(0,0)

Ch = (10,5)


a1a2

x

y

Each face is made of approximately 150 million tiny carbon nanotubes; that's about how many Americans voted in the 2008

presidential election.04/09/23 32Copywrite:M.Tech-VLSI,Techno India,Salt Lake

Different Nano Tube STM Pictures

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BIBLIOGRAPHYBIBLIOGRAPHY www.google.com www.wikipedia.com Geometry of Carbon Nano Tube By Ehsan

Ban,Sara Kadkhodaie,Dept. of Civil Engg. Sharif University of Technology,Tehran,Iran.

An Intoduction To Carbon Nano Tube By Tom Grace, Prof. Hongjie Dai,Dept. of Chemistry, Stanford University.

http://www.nccr/nano.org/nccr/media/gallery/gallery_01/gallery_01_03

http://www.photon.t.utokyo.ac.jp/~maruyama/agallery/nanotubes

Carbon Nano Tube By Dr. Somenath Chatterjee, [email protected]


With Sincere Regards To Dr.Somnath Chatterjjee.


nano tube geometry1

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