Carbon Engineering

NanocarbonStructures

DiamondFullerenesCarbon nanotubes (CNT) multiwalled (MNT)Diamond Like Carbon (DLC)GrapheneNanospheres

Allotropes of Carbon

Carbon

Crystalline

Diamond

Graphite

Amorphous

Coal

Coke

Gas Carbon

Charcoal

Plant

Wood Charcoal

Sugar Charcoal

Animal

None Charcoal

Blood Charcoal

Lamp Black

Carbon Compounds and Materials

The C atom:

Atomic number 6

Atomic mass 12

Ground state electron configuration

1s22s22p2

Ionization potential 11.26 eV

First excited state 4.18 eV

GS term -3P

First excited state term 1s22s2p3 5S

Carbon Compounds and MaterialsForms what type of bonds?

Valence electrons -

Forms strong, directional covalent bondsValence electrons - 2s22p2

Energy difference between 2s and 2p orbital is about 4 eV

Bonds more easily from first excited state 2s2p3

Bond energy is about 4 eV per bond

Different hybridisation - different bonds

Bonding in carbon

One of the reasons why carbon is so interesting as an element and as an engineering material is that it has three rather different ways in which it can form bonds. The resulting properties vary widely.

Shells & Orbitals

Carbon has 6 electrons, so we would expect this electronic configuration

Hybridisation

sp

sp3

sp2

fullerine

CNT

graphite

carbynes

Diamond like Carbon

Carbon Compounds and Materials

Carbynes1 dimensional solidPolymer of sp hybridised C chainsNot very stable (high T and P)Reported for rapidly quenched carbons

Carbon fibres2-D solidMacroscopic analog of nanotubesGraphite related materialGrown from thermal decomposition of hydrocarbons in gas phase in presence of transition metal catalyst particleLayered structure, but not a ‘perfect’ structure

Carbon Compounds and Materials

Diamond3 dimensional solidCovalent network of sp3 hybridised C atoms109.5 C bond angleSolid at room temperatureHigh melting pointHardClear

Carbon Compounds and Materials

GraphiteSheets of sp2 hybridised C atoms120 bond angle 2 dimensional solidSheets weakly bonded by p orbitals

Hexagonal crystalLattice parameters a = 0.2464 nm, c = 0.6711Density = 2.26 g/cm3

C-C bond length 0.142 nmSemi-metalWide band gap semiconductorBandgap = 5.47 eV

Graphite

http://www.edinformatics.com/interactive_molecules/graphite.htm

image : Wikipedia

Graphene

GraphenePossible applications:

spintronics

ultrafast photonic devices (non-linear optical property)

sensors for gas molecules (surface area, effect on resistance argument)

ribbons of graphene as interconnects?

ballistic transistors (low on-off ratio and gain though <40)

Feb.2010 IBM researchers switch graphene transistor at 100 GHz!!!

transparent conducting electrodes/coatings

ultra-capacitor electrodes

lithium ion cell anodes

Graphene

Grapheneonly one atom thick, optically transparent, chemically inert, and an excellent conductor.

Some facts• Strongest material foundStrength

• Wonderful candidate for photovoltaics• Absorb phonons at all frequenciesNo band gap

• Unimpeded flow of electrons at RT• Similar to superconductivity but at RT

Ballistic conduction

• the highest current density (10^6 that of copper) at RT• highest intrinsic mobility (100 times more than in silicon)• conducts electricity in the limit of no electrons

Best at electricity?

• Only absorbs 2.3%• Good for solar cells and touch screensTransparency

• 20% elongationElastic

• Beats diamond• Best conductor knownThermal conductivity

•most impermeable material ever discovered•Even helium atoms cannot squeeze through•great material for building highly sensitive gas detectors

Impermeable

Where does all this lead?

Perfect graphenes consist exclusively of hexagonal cells;pentagonal and heptagonal cellsconstitute defects. If an isolated pentagonal cell is present, then the plane warps into a cone shape; insertion of 12pentagons would create a fullerene. Likewise, insertion of an isolated heptagon causes the sheet to become saddle-shaped.Controlled addition of pentagons and heptagons would allow a wide variety of complex shapes to be made, for instance carbon NanoBuds. Single-walled carbon nanotubes may be considered to be graphenecylinders; some have a hemispherical graphene cap (that includes 6pentagons) at each end.

Graphene productionGraphene sheets in solid form (e.g. density > 1g/cc) is presently one of the most expensive materials on Earth.

Researchers obtained relatively large graphene sheets (eventually, up to 100 micrometers in size and visible through a magnifying glass) by mechanical exfoliation (repeated peeling) of 3D graphite crystals.

Another method is to heat silicon carbide to high temperatures (1100°C) to reduce it to graphene.

Properties of GrapheneThe resistivity of the graphene sheet is 10^ 6

·cm, less than the resistivity of silver, the lowest resistivity substance known at room temperature.

Graphene is the strongest substance known to man. Its Young's modulus is 0.5 TPa, which differs from bulk graphite.

These intrinsic properties could lead to the possibility of utilizing Graphene for NEM systems applications such as pressure sensors, and resonators.

Properties of GrapheneEngineering professors at Columbia University tested graphene's strength at an atomic level by indenting a perfect sample of the material with a sharp probe made of diamond.

Electrons move through graphene with almost no resistance, generating little heat. What's more, graphene is itself a good thermal conductor, allowing heat to dissipate quickly.

Graphene and ApplicationsBy oxidizing graphene flakes, and then floating them in water, the graphene flakes form a single sheet and bond very powerfully called Graphene oxide paper.

Applications:Membranes with controlled permeability

Supercapacitors for energy applications.

Graphene electronics could be useful for communications and imaging technologies that require ultrafast transistors.

How to grow graphene

Two ways

CVD

Typically from methane C2H2 gas

growth automatically stops after a single layer of graphene

has formed at low P

Growth from a solid C source

depositing a source of carbon on a metal catalyst

substrate

using an 800° furnace to grow the graphene across the

catalyst

The fast and the flexible: Graphene foam batteries charge quickly

Capacity on par with existing lithium batteries, but charges in 15 minutes.

http://arstechnica.com/science/2012/10/the-fast-and-the-flexible-graphene-foam-batteries-charge-quickly/

A graphene FET, or field-effect transistor

consists of a single ribbon of graphenewith one side laid down on a positive electrode, the other laid down on a negative one. A third electrode, or gate, can then modulate the flow of electrons through the ribbon, turning the device into a switch

GRAPHENE GOODNESS

might include:a flexible video display incorporated into a shower curtain,

camouflage clothing, and

a virtual-reality theatre in the round.

Illustration: James Provost

Defects?

An artist's conception of a row of intentional molecular defects in a sheet of graphene. The defects effectively create a metal wire in the sheet. This discovery may lead to smaller yet faster computers in the future. Image Credit: Y. Lin, USF

Synthetic Diamonds

cannot reach actual conditionsHPHT technique vs CVDuse a catalyst, Ni Co or Fevery high pressure pressurecurrent production, 5 to 10 GPa, usually < 1 carat (200 mg)brown due to nitrogen contaminationcan be removed using eg Al but growth is slower6 weeks to grow a 25 carat diamond (5 g)

diamond-like coatings

decompose a gas, eg CH4 on a substratesecret projects in USA and Soviet Union in 1950sfirst reports in 1960’s (on diamond substrates)success on Si and other substrates 1970sexplosion of interest in 1980s and onwards27 KPa, 500-800°C decompose feedgasmethane + hydrogen streamenergise with microwave, laser, electric arc, electron beam etchydrogen etches away any non-diamond carbonnot much industrial impact, mostly people in universities!

Fullerenessomewhat accidental discovery, found in soot!

buckminsterfullerene C60, made in 1985 by Robert Curl, Harold Kroto and Richard Smalley

‘buckyballs’

any molecule composed entirely of carbon, in form of hollow sphere, ellipsoid or tube

image : Wikipedia

BuckyballsBuckminsterfullerene, is composed entirely of carbon atoms.Each carbon atom on the cage surface is bonded to three carbon neighbors therefore is sp2 hybridized.A total of 60 carbon atoms are present forming a sphere consisting of five-carbon and six-carbon atom rings arranged in the same pattern as a modern soccer ball. It is just less than a nanometer in size.As well as C60, other sized balls have been created.Unlike other forms of carbon, fullerenes may be soluble, as shown in the photograph below. C60 is pink and C70 is red in solution.

38What are fullerenes?

Other relatively common clusters are C70, C72, C74, C76, C80, C82 and C84 (plenty of others, higher or lower than C60, exist too but less abundant in the experimentally produced mixture fullerene soot).

39What are fullerenes? (continued…)

C60

C70

Fullereneshow are they made?

+ -

e-

image : Wikipedia

extract in toluene

filter to remove impurities

HPLC to purify fractions

He

Fullerenes• applications? Michalitsch 2008

• initial hype has died down

• 2% of all nanotech patent (vs 10% for carbon nanotubes)

• anti-oxidants, radical scavengers, L’Oreal has many patents!

• but most patents point to use as ingredient on organic electronic devices

• e.g. photovoltaics, photodiodes

• absorb visible and UV light strongly

• drug delivery

• thermally stable lubricants

• fuel cell electrodes

• printable conductive inks

• electrically conducting polymers

Fullerene

Symmetric shape lubricant

Large surface area catalyst

High temperature (~500oC)High pressureHollow

caging particles

Ferromagnet?- polymerized C60

- up to 220oC

Properties

UsesThey have many chemical synthetic and pharmaceutical applications.

Fascinating electrical and magnetic behaviour including superconductivity and ferromagnetismC60 is an optical limiter.

When light is shone on it, a solution of fullerene-60 turns darker instantly and the more intense the light, the darker it gets, so the intensity of transmitted light is limited to a maximum value.

design of safety goggles in intense light situations e.g. people working with laser beams.

Fullerenes may used in certain medical applications - nanomedicineThe idea is to use the very small fullerene molecules to easily deliver drugs directly into cells in a highly controlled manner.

The extremely small diameter of the nanoparticle fullerenes (which act like a cage to hold the drug) allows them to readily pass through cell membranes.

Fullerenes are being developed that have excellent lubricatingproperties (maybe superior to lubrication oils)

from reducing friction in moving metal parts of machines from cog wheels to ball bearings and maybe artificial joints after orthopedic operations on hips and knees!

Nanocar

Shirai, Y. et al. (2005). Nano Lett. 5: 2330

Don’t forget poor old graphite!!!!!!

ReferencesGraphene http://en.wikipedia.org/wiki/Grapheneaccessed on March, 29 2009

Graphene Confirmed the World’s Stronged Known Material http://gizmodo.com/5026404/graphene-confirmed-as-the-worlds-strongest-known-material accessed on March, 29 2009

Nanotechnology Reserchers go Ballistic Over Graphene http://www.nanowerk.com/spotlight/spotid=2340.php accessed on March 29, 2009

TR10: Graphene Transistors http://www.technologyreview.com/read_article.aspx?ch=specialsections&sc=emerging08&id=20242 accessed on March 29, 2009

Graphene: Charged Up http://www.natureasia.com/asia-materials/highlight.php?id=77 accessed on March 29, 2009

Carbon