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Structure of matter

Lec. (7)

www.scifun.ed.ac.uk/card/flakes.html

Graphite – Van der Waals Bonds

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Graphite

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Soft and slippery Many strong covalent bonds holding the structure together

but only in 2 dimensions. The layers are free to slide easily

over one another. Graphite powder is used as a lubricant.

Brittle

All of the bonds are directional within a layer and stress

across a layer will tend to break them. Graphite rods used for

electrolysis easily break when dropped.

Electrical conductor

Only three of the valence (outer shell) electrons are used in

sigma bonding. The other electron is in a 'p' orbital which can

overlap laterally with neighbouring 'p' orbitals making giant

molecular pi orbitals that extend over the whole of each layer.

Electrons are free to move within these delocalised pi

orbitals.

Insoluble in water.

There are only very weak Van der Waal's attractions between

the carbon atoms and the water molecules whereas the

carbon atoms are bonded very tightly to one another.

Very high melting point

Many strong covalent bonds holding the layers together - it

requires massive amounts of energy to pull it apart

Graphite

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Diamond

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Hard Many strong covalent bonds holding the structure

together.

Brittle All of the bonds are directional and stress will tend to

break the structure (In a malleable substance, such as

for example a metal, the bonding is non-directional and

can still act if the particles are displaced with respect to

one another).

Insulator All of the valence (outer shell) electrons are used in

bonding. The bonds are sigma and the electrons are

located between the two carbon nuclei being bonded

together. None of the electrons are free to move

Insoluble in water. There are only very weak Van der Waal's attractions

between the carbon atoms and the water molecules

whereas the carbon atoms are bodned very tightly to

one another.

Very high melting point Many strong covalent bonds holding the structure

together - it requires massive amounts of energy to pull

it apart

Diamond

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Diamond

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Properties &

Applications

• Electrical

• Mechanical

• Thermal

• Storage

Nanocarbon

http://www.youtube.com/watch?v=4yRjYiw_H_s

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Discovered in 1985

Nobel prize Chemistry 1996

Curl, Kroto, and Smalley

Fullerenes

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Buckyballs

C60

32 facets

(12 pentagons and 20

hexagons)

C70, C76, and C8410

Bucky Balls

• Symmetric shape

→ lubricant

• Large surface area

→ catalyst

• High temperature (~750oC)

• High pressure

• Hollow

→ caging particles11

Buckyballs

• Forms a crystal by weak van der

Waals force

• Superconductivity

- K3C60: 19.2 K

- RbCs2C60: 33 K

Kittel, Introduction to Solid State Physics, 7the ed. 1996.

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Buckyballs

• Forms a crystal by weak van der

Waals force

• Superconductivity

- K3C60: 19.2 K

- RbCs2C60: 33 K

http://invsee.asu.edu/nmodules/Carbonmod/crystalline.html

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Soft and slippery Few covalent bonds holding the molecules together but

only weak Vander Waals forces between molecules.

Brittle Soft weak crystals typical of covalent substances

Electrical Insulator No movement of electrons available from one molecule

to the next. The exception could be the formation of

nano-tubes that are capable of conducting electricity

along their length. These are the subject of some

experiments in micro electronics

Insoluble in water. There are only very weak Van der Waal's attractions

between the carbon atoms and the water molecules

whereas the carbon atoms are bonded very tightly to

one another in the molecules.

Low Melting Point Solids Typical of covalent crystals where only Van der Waal's

interactions have to be broken for melting.

Buckyballs

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Carbon Nanotubes (CNT)

• Like graphite but all coiled up

• Typically 10 Angstroms in diameter

• Can be electrically conductive or semiconducting

• SWNT and MWNT

– Composites, transistors, hydrogen storage

Courtesy of and ©Copyright Professor Charles M. Lieber Group

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Nanotube

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The "armchair" type has the characteristics of a metal

The "zigzag" type has properties that change depending on the tube diameter

The "spiral" type has the characteristics of a semiconductor

Armchair

Zigzag

Spiral

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Nanotube

Zheng et al. Nature Materials 3 (2004) 673.

SWCNT – 1.9 nm

Diameter:

as low as 1 nm

Length:

μm to cm

High aspect ratio:

1000diameter

length

→ quasi 1D solid

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Nanotube Intro Video

• Earth and sky: Properties of Nanotubes• http://www.youtube.com/watch?v=zQAK4xxPGfM&mode=related&search=Nanotube

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Introduction

A carbon nanotube (CNT) is

a tubular molecule with

axial symmetry and

diameter in the

nanometer range

(Muller).

It can be considered as a

rolled up graphene sheet.

However, it possesses

many properties that

leave no doubt this is not

just graphene.

http://www.nanotech-now.com/nanotube-buckyball-sites.htm

http://www.msm.cam.ac.uk/phasetrans/2005/paper/img19.png

Types

• Single Walled CNT (SWCNT): one-atom-thick CNTs

• Multi Walled CNT (MWCNT): concentric layers of CNTs

http://www-ibmc.u-strasbg.fr/ict/images/SWNT_MWNT.jpg

Properties

Among some of the

properties of the CNTs

we can find:• Electrical: Both metallic and non-

metallic behaviors are observed,

while geometry plays a profound

part in determining the electronic

behavior. (Ebbesen)

• Elastic: Tensile Young’s module and

torsion shear module comparable to

that of diamond (Lu).

http://www.studentsoftheworld.info/sites/family/img/27335_Electricity.jpg

http://www.nanoshel.com/research-center/wp-content/uploads/2009/01/ballistic-impact.jpg

Properties

• Mechanical: Carbon nanotubes have high strength plus extraordinary flexibility and resilience. (Salvetat)

• Thermal: Thermal expansion of carbon nanotubes will be essentially isotropic that is, uniform in all directions (Ruoff).

http://brent.kearneys.ca/wp-content/uploads/2006/05/carbon_nanotube.jpg

Nanotube Stats• Current capacity

Carbon nanotube 1 GAmps / cm2

Copper wire 1 MAmps / cm2

• Thermal conductivity

Comparable to pure diamond (3320 W / m.K)

• Temperature stability

Carbon nanotube 750 oC (in air)

Metal wires in microchips 600 – 1000 oC

• Caging

May change electrical properties

→ can be used as a sensor

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NanotubesCarbon nanotubes are the strongest known material.

• Young Modulus (stiffness):

Carbon nanotubes 1250 GPa

Carbon fibers 425 GPa (max.)

High strength steel 200 GPa

• Tensile strength (breaking strength)

Carbon nanotubes 11- 63 GPa

Carbon fibers 3.5 - 6 GPa

High strength steel ~ 2 GPa

• Elongation to failure : ~ 20-30 %

• Density:

Carbon nanotube (SW) 1.33 – 1.40 gram / cm3

Aluminium 2.7 gram / cm3

E

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Synthesis of Carbon Nanotubes

• IFW-Dresden Carbon Nanotubes• http://www.youtube.com/watch?v=tgToxaOqF10&mode=related&search=Nanotube

• Synthesis of Carbon nanotube• http://www.youtube.com/watch?v=8N79nlhwcgM&mode=related&search=C60%20Ful

lerene%20Fullereno%20Buckyball

• Growth of Carbon nanotube• http://www.youtube.com/watch?v=1p8vFdCJRZE&NR=1&feature=fvwp

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http://www.youtube.com/watch?v=HIGMB_R3pgI&feature=related

http://www.youtube.com/watch?v=nTbz8w1SB1U&feature=fvw

Water Resistant Coatings

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Carbon Fiber

A 6 μm diameter carbon filament

(running from bottom left to top

right) compared to a human hair.

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Sports Equipment

CNT Carbon Nanotube Opti-Flex composite handle technology,

provids maximum handle flex-three times greater than aluminum

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Carbon Nanotube/Cement

Composite Systems

In concrete, they increase the tensile strength, and halt crack propagation.33

www.nanooze.org

The Space Elevator

http://www.youtube.com/watch?v=lVV0S9cNLKI&feature=related

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www.enterprisemission.com 35

Space Elevator

• NOVA space elevator intro• http://www.youtube.com/watch?v=pnwZmWoymeI&

mode=related&search

• 2 minute space elevator intro• http://www.youtube.com/watch?v=F2UZDHHDhog

• Space Elevator Competition: USST's First Place Climb

• http://www.youtube.com/watch?v=VkdfuQdoW_Q&mode=related&search=space-elevator%20turbo%20crawler

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CNT light bulb filament:

alternative to tungsten filaments in

incandescent lamps

The average efficiency is 40% higher than that of a tungsten filament at the

same temperature (1400–2300 K).37

Nano Radio

•http://nsf.gov/news/news_summ.jsp?cntn_id=110566

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•http://nsf.gov/news/news_summ.jsp?cntn_id=110566

When a radio wave of a specific frequency impinges on the

nanotube, it begins to vibrate vigorously.

An electric field applied to the nanotube forces electrons to be

emitted from its tip.

This electrical current may be used to detect the mechanical

vibrations of the nanotube, and thus listen to the radio waves.

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Nanotube Radio

• http://www.youtube.com/watch?v=gkQkzvnstkg

• http://www.youtube.com/watch?v=yQz9C7yE1kc

&feature=related

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Carbon Nanotube

Electronics• Carbon nanotube in microchip• http://www.youtube.com/watch?v=74YkJYT7Uj4&mod

e=related&search=Nanotube

• Customized Y-Shaped Nanotubes• http://www.youtube.com/watch?v=SGWHBQQKmOs

Transistors – the active component of virtually all electronic devices, are what we

refer to as electronic switching devices. In a transistor, a small electric current can

be used to control the on/off of a larger current. 41

Semiconducting CNTs have been used to fabricate field effect transistors (CNTFETs).

The electron mean free path in SWCNTs can exceed 1 micron (this is very large)

therefore it is projected that CNT devices will operate in the frequency range of

hundreds of GHz.

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Kavli Institute Delft

SEM image of superconducting transistors 43

CNT-FED

Professor George Lisensky

http://mrsec.wisc.edu/Edetc/cineplex/nanoquest/applications.html44

CNT-FED

Carbon nanotubes can be electrically conductive and due to their small diameter of

several nanometers, they can be used as field emitters with extremely high efficiency

for field emission displays (FED). The principle of operation resembles that of the

cathode ray tube, but on a much smaller length scale.

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Bucky Paper

A thin sheet made from nanotubes that are 250 times stronger than steel and 10

times lighter that could be used as a heat sink for chipboards, a backlight for LCD

screens or as a faraday cage to protect electrical devices 46

Warwick ICAST

http://www.youtube.com/watch?v=i4Ax8sY2U4A&mode=related&search=Nanotube

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Hydrogen StorageCarbon nanotubes covered in titanium atoms provide a very efficient method for

storing hydrogen.

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'Artificial muscles' made from

nanotubes

"Artificial muscles" have been made from millions of carbon nanotubes. Like natural

muscles, providing an electrical charge causes the individual fibers to expand and

the whole structure to move. 50

Bone cells grown on

carbon nanotubesResearchers at the University of California, Riverside have published findings

that show, for the first time, that bone cells can grow and proliferate on a scaffold

of carbon nanotubes. Scientists found that the nanotubes, 100,000 times finer

than a human hair, are an excellent scaffold for bone cells to grow on.

http://biosingularity.wordpress.com/2006/03/21/researchers-grow-bone-cells-on-

carbon-nanotubes/

http://neurophilosophy.wordpress.com/2006/03/17/123/ 51

Nano SQUID

A SQUID is a superconducting interferometer device. SQUID devices can be used to

monitor infinitesimally small magnetic fields or currents. The originality of this work, is

to use gate-tunable carbon-nanotubes (CNT) for the Josephson junctions. The device

combines features of single electron transistors with typical properties of a SQUID

interferometer. The gate tunability of the CNT junctions enhance the sensitivity of the

device which can in principle detect the spin of a single molecule. 52