Hanoi -2012Class: Material Science EngineeringStudent : Hoang Van Tien

DID YOU KNOW?

Carbon nanotubes, composed of interlocking carbon atoms, are 1000x thinner than an average human hair – but can be 200x stronger than steel.

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Definition Theory and properties Synthesis Potential and current applications Challenges and future

What are carbon nanotubes

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CNT: Rolling-up a graphene sheet to form a tube

Schematic of a CNT

STM image of CNT

Carbon nanotubes are hexagonally shaped arrangements of carbon atoms that have been rolled into tubes.

These tiny straw-like cylinders of pure carbon have useful electrical propeties. They have already been used to make tiny transistor and one-dimentional copper wire

Types of CNTs

Single Wall CNT (SWCNT)

Multiple Wall CNT (MWCNT)

Can be metallic or semiconducting depending on their geometry.

Single- walled-Most single-walled nanotubes (SWNTs) have a diameter of cloes to 1 nanometer,with a tube length that can be many millions of time longer-The structure of a SWNTs can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene in to a seamless cylender

If:m=0 , the nanotubes are called zigzagn=m ,the nanotubes are called armchairOtherwise ,they are called chiral

Multi-walled Multi-walled nanotubes (MWNTs)

consist of multiple rolled layer( concentric tubes) of graphene

Triple-walled armchair CNTs

 In the Russian Doll model, sheets of graphite are arranged in concentric cylinders, e.g., a (0,8) single-walled nanotube (SWNT) within a larger (0,17) single-walled nanotube.

In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper.

The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å. The Russian Doll structure is observed more commonly. Its individual shells can be described as SWNTs, which can be metallic or semiconducting. 

compare

Single –walled CNTs exhibit electric properties that are not shared by the multi-walled CNTs variant

SWNTs is useful in the development of the first intramolecular field effect transistors (FET)

torus-Torus is theoretically described as carbon nanotube bent into a torus (doughnut shape) .

-Nanotorus are predicted to have many unique properties such as :

+magnetic moments +thermal stability …

-Vary widely depending on radius of the torus and the radius of the tube

nanobud

In nanotechnology,carbon nanobuds form a material (discovered and synthesized in 2006) which combines two previously discovered allotropes of carbon: carbon nanotubes and spheroidal fullerences   (or, in short, fullerenes)

fullerenes are covalently bonded to the outer sidewalls of the underlying nanotube

=>>>> Has useful properties of both fullerenes and carbon nanotubes

Extreme carbon nanotubes-The observation of the longest carbon nanotubes (18.5 cm long) was reported in 2009. These nanotubes were grown on Si substrates using an improved chemical vapor deposition (CVD) method and represent electrically uniform arrays of single-walled carbon nanotubes.

-The shortest carbon nanotube is the organic compound cycloparaphenylene

-The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å. This nanotube was grown inside a multi-walled carbon nanotube

-The thinnest freestanding single-walled carbon nanotube is about 4.3 Å in diameter

PROPERTIES OF CARBON

NANOTUBES

Strength and elasticity

CNTs are expected to be the ultimate high-strength filber Single wall carbon nanotubes

are stiffer than steel and are very resistant to damage from physical forces

Carbon Nanotubes (CNTs) very useful as probe tips for very high-resolution scanning probe microscopy. 

elasticity

-The current Young’s modulus value of single walled carbon nanotubes is about 1 terapascal

-The modulus of the multi walled carbon nanotubes correlates to the amount of disorder in the carbon nanotube walls

-when multi walled carbon nanotubes break, the outermost layers break first

Comparison of mechanical propertiesMaterials Young’modulus(T

pa)Tensile strength(Gpa)

Elongation at break(%)

SWNTE ~1 (from 1 to 5) 13-53 16

Armchair SWNTT

0.94 126.2 23.1

Zigzag SWNTT 0.94 94.5 15.6-17.5

Chiral SWNT 0.92

MWNTE 0.2-0.8-0.95 11-63-150

Stainless steelE

0.186-0.214 0.38-1.55 15-50

Kevlar-29&149E

0.06-0.18 3.6-3.8 ~2

EExperimental observation;  TTheoretical prediction

Electrical properties

For a given (m,n) nanotubes: If n=m(armchair)

the CNTS is metalic If n-m is multiple

of 3 ,the CNTs is semiconducting with a small band gap

Otherwise ,the CNTs is moderates semiconductor

Thermal property

All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction ", but good insulators laterally to the tube axis. 

SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1.

in copper : 385 W·m−1·K−1

 A SWNT has a room-temperature thermal conductivity across its axis (in the radial direction) of about 1.52 W·m−1·K−1. (same as oil)

defect

As with any material, the existence of a crystallographic defect affects the material properties.

Because of the very small structure of CNTs, the tensile strength of the tube is dependent on its weakest segment in a similar manner to a chain, where the strength of the weakest link becomes the maximum strength of the chain.

Crystallographic defects also affect the tube's electrical properties and thermal properties.

Toxicity .

Under some conditions ,nanotubes can cross membrane barriers ,which suggests that if raw materials reach the organs, they can include harmful effects such as inflammatory and fibrotic reactions

CNTs were capable of producing  inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs

=>>>carbon nanotubes can pose a serious risk to human health

synthesis

Techniques have been developed to produce carbon nanotubes in sizeable quanlities ,some of them are:- Arc discharge- Laser ablation - Chemical vapor deposition(CVD)

Arc discharge

Nanotubes were observed in 1991 in the carbon soot of graphite electrodes during an arc discharge, by using a current of 100 amps , that was intended to produce fullerenes.

 the carbon contained in the negative electrode sublimates because of the high-discharge temperatures.

The yield for this method is up to 30% by weight and it produces both single- and multi-walled nanotubes with lengths of up to 50 micrometers with few structural defects

Laser ablation

a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber.

Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses.

A water-cooled surface may be included in the system to collect the nanotubes.

The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature . However, it is more expensive than either arc discharge or chemical vapor deposition.

Chemical vapor deposition a substrate is prepared with a layer of metal catalyst

particles, most commonly nickel, cobalt, iron , or a combination.

The substrate is heated to approximately 700°C. two gases are bled into the reactor: a process gas

(such as ammonia , nitrogen or hydrogen ) and a carbon-containing gas (such as acetylene , ethylene , ethanol or methane ).

>>Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes.

Laser-assisted thermal chemical vapour deposition

the growth mechanism .

Sources of laser:a medium power, continuous wave CO 2 laser,perpendicularonto a substrate,

pyrolyses sensitised mixtures of Fe(CO) 5 vapour and acetylene in a flow reactor.

Catalyst: Fe (very small iron particles)

Substrate: sillica.iron pentacarbonyl vapour, +ethylene +acetylene

single- and multi-walled carbon nanotubes

Purification

The main impurities :graphite (wrapped up) sheets, amorphous carbon, metal catalyst and the smaller fullerenes…

Rules :-separate the SWNTs from the impurities

- give a more homogeneous diameter or size distribution.

The techniques that will be discussed are oxidation, acid treatment, annealing, ultrasonication, micro filtration, ferromagnetic separation, cutting, functionalisation and chromatography techniques.

applications

Field emission Nanotube sensors Nanotube transistors Nanotubes as SPM tips Energy Storage Conductive Adhesives and Connectors Biomedical Applications……….

Nanotubes are rolled-up graphene sheets, and graphene is one of the stiffest materials when subjected to deformations parallel to the sheet.nanotubes show exceptional mechanical properties, especially a high strength-to-weight ratio.

Applications:

Schematics of a nanotube transistor, with some measurements.

Use of a MWNT as AFM tip. VGCF stands for Vapour Grown Carbon Fibre. At the centre of this fibre the MWNT forms the tip.the VGCG provides a convenient and robust technique for mounting the MWNT probe for use in a scanning probe instrustment

Space elevator

 Faster computer chips

cancer treatment

Use carbon nanotubes as drug delivery tools

Challenges and potentials

Potentials :  the new wonder material, can useful in many

types of industry ,especially in electronics applications

The field of research for CNTs has become so broad over the past 20 years that they are being tested for use in fields .

Challenges : Too expensive (~ $ 200per gram) toxicological issues. hard to purification and the ability to

manipulate structures at the atomic scale….

summary

Carbon nanotubes have very different properties compared to the other carbon allotropes- these unique properties offer huge potential in product development.

Nanomaterials, particularly carbon nanotubes (CNTs), hold great promise for a variety of industrial, consumer, and biomedical applications, due to their outstanding and novel properties.

sources

1. D.A.Bochvar and E.G.Gal'pern, Dokl.Akad.Nauk.USSR, 209, (610, 1973 )

2.http://www.ou.edu/engineering/nanotube, 2003

3. http://nanotube.msu.edu/4.http://www.pa.msu.edu/cmp/csc/

nanotube.htm55.http://en.wikipedia.org/wiki/Carbon_nanotube6.http://students.chem.tue.nl/carbonnanotubes/applications.html

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