GRAPHENE SYNTHESIS METHODS

BY AAMIR

MUSHTAQ ROLLNO

MTNT-01

INTODUCTION TO GRAPHENE

Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice

The name ‘graphene’ comes from graphite + -ene = grapheneGraphene –the mother of all graphitese

High resolution transmission electron microscope images (TEM) of graphene

Molecular structure of graphene

Andre Geim(Born 1958 and educated in Russia, Dutch, University of Manchester UK)

Konstantin Novoselov(Born 1974 in Russia, educated in the Netherlands, Russian & British, University of Manchester UK)

2010 Nobel Physics Prize

"for groundbreaking experiments regarding the two‐ dimensional material graphene"

Extraordinary Properties

Strongest material ever measured: σ=1.0 TPa.

Thinnest material, largest area: one atomic layer, 2630 m2/g.

Very flexible: flexible devices, wearable devices.

Record thermal conductivity: 5000 W/ mK.

Negative thermal expansion co efficiency.

Extremely high electrical carrier mobility: two order higher than Si Sustain high current density: six order of magnitude higher than Cu

Zero effective mass: a cute toy for solid-state physicist.

Completely impermeable (even He atoms cannot squeeze through)

Methods for Synthesis of Graphene

1 Chemical vapor deposition2 Epitaxial growth3 Pyrolysis

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4 Mechanical cleavage5 Electrolytic exfoliation6 Chemical synthesis through oxidation of graphite

Chemical vapor deposition

•Hydrocarbon can be deposited on thin sheet of copper to produce thick layer of graphite.•Annelead at 1000 c to convert the amporphous flim to the polycrystalline phase.•Methane flow rate= 12sccm.•hydrogen flow rate =24sccm.•Pressure =10 torr.•temp-=800-1050 degree celsius •Time=30 sec to 15 min.•Then quick cooling.•Methane is a relatively stable hydrocarbon compound due to strong C-H bond, as a result, decomposition occurs at elevated temperature

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.Time=30 sec to 15 min.Then quick cooling.

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Epitaxial growth - SiC decomposition

• When SiC substrates are annealed at high temp. • Si atoms selectively desorb from the surface.

• The C atoms left behind naturally form FLG (few-layer graphene).

MECHANICAL CLEAVAGE:peeling off layers of graphite with a sticky

tape

transfer onto substrate

optical microscope image ofresulting flakes

Electrochemical synthesis of graphene sheets: It is a one step treatment.

In this case, two high purity graphite rods are used as electrodes.

In the electrochemical cell they are immersed in the electrolyte bath composed of ionic liquid and water.

Static potential is applied to the two electrodes. Under these conditions the anode is corroding and a black precipitate is gradually appearing in the reactor.

After electrolysis stable graphene dispersion is obtained.

washed and dried to obtain bulk powders of graphene

Chemical synthesis - graphene from graphene oxide:

The method involves the synthesis of graphite oxide by oxidation of graphite in presence of strong acid.

Dispersing the flakes by sonication.When graphite turns in to graphite oxide, interlayer

spacing is increased 2-3 times.Spacing can be further increased by inserting polar

liquid such as sodium hydroxide.As result interlayer distance further

increased,which infact separates single layer from bulk material.

Graphite oxide reduce back to graphene using Hydrazine.

OTHER METHODS:Dry ice method:For high yield of graphene by burning magnesium metal in dry ice.A simple method but where the products have not been fully

characterized.

From sugar:Sucrose can be quickly converted in to graphene via application to a

copper nickel substrate & being subjected to 800 degree celsius under low pressure with exposure to argon & hydrogen.

This process takes 10 minutes and scalable for industrial production.

Unzipping of carbon nanotubes: Research group reported the unzipping of nanotube by different

chemical process. They reported the opening of side wall of CNTs by a step by step a

solution based oxidation process using sulphuric acid and potassium permagnet and water.

successive increase in potassium permagnet concentration in a solution results in large degree opening of MWCNTs.

Mechanical exfoliation: Advantages Low-cost and easy. No special equipment needed.

Disadvantages Not suitable for large scale production. Labor intensive.

Epitaxial growth: Advantages Large scale fabrication of graphene on an isulator or semiconductor surface Large scale area.Disadvantages High growth temperature and very low pressure. Difficult control of morphology and adsorption energy.

Graphene oxideAdvantages• Low in cost• Low temperature process. Disadvantages• Small yield ,defective grahene,Partially reduced graphene oxide•hazardous gases.

Chemical vapour deposition : Advantages Thickness control, large size. High quality. Disadvantages Existence of defects. Small scale production.

Unzipping of carbon nanotube: Advantages Size controlled by selection of starting nanotube.

Disadvantages Expensive. Starting material.

PYROLYSIS: AdvantagesSimple and possible mass production. DisadvantageQuality is not good.Contains a large number of defects.

THANKS