Graphene is the world’s first 2-D material and is the thinnest, strongest, and most flexible material known to exist. Graphene is a special form of carbon that can conduct electricity and heat better than anything else. It was discovered in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester and they got Nobel Prize for this in 2010.
In this article, you will learn about the fundamentals of graphene and how this material offers new insights into nanotechnology and quantum physics. Graphene offers a wealth of potential future applications; in composites, solar cells, sensors, superchargers etc.
Let’s study in detail about this wonderful material.
STRUCTURE:-
Graphene is a crystalline allotrope of carbon with 2-D properties and has a perfect hexagonal lattice as shown in figure below.
Graphene’s hexagonal lattice can be regarded as two interleaving triangular lattices. Graphene’s stability is due to its tightly packed carbon atoms and sp2 orbital hybridization. This unique structure of Graphene results in zero band gap between the valence band and conduction band when exist in single layer and this band gap varies with layers and external forces like electric field.
HOW TO MAKE IT:-
There are mainly three methods of making or extracting Graphene form graphite which are explained below in brief. We will study these methods in detail in my next article on Carbon Nanotubes.
Method 1: Mechanical Exfoliation
- A sticky tape is placed on to a block of graphite and then peeled back, stripping a thin layer off the top.
- This layer of carbon is thinned further by pressing it on to other layer of tape.
- The tape is finally pressed onto a very smooth substrate such as silicon then peeled off, leaving a graphene layer a single atom thick.
Sample Size: Greater than 1mm.
Application: Research.
Method 2: Chemical Exfoliation via Graphene Oxide.
- Graphite pellets are first oxidised.
- Pellets exfoliated in chemical solution to produce mono-layers of graphene oxide.
- This solution is processed by centrifuge.
- Solution is deposited on a substrate and reduced (chemically or thermally) to parent graphene state.
Sample Size: Infinite but with larger flake size than simple chemical exfoliation.
Application: Coating, paint, ink, composites, transparent conductive layer energy storage and bio applications.
Method 3: Chemical Vapour Deposition
- A substrate (usually copper) is heated in a furnace at low pressure to about 1000◦C. This anneals the copper.
- Methane and Hydrogen gas are allowed to flow through the furnace. Methane acts as a carbon source and Hydrogen helps in controlling the deposition of graphene on substrate.
- Carbon atoms from the methane are deposited on to the copper. They crystallise as a continuous graphene sheet.
Sample Size: About 1 mm.
Application: Photonics, Nano electronics, transparent conductive layer sensors and bio applications.
PROPERTIES:-
1. Strength:
Graphene is the strongest material ever known and its extraordinary strength lies in the robustness of the covalent carbon-carbon bond. Large-angle-bent graphene monolayer has been achieved with negligible strain, showing mechanical robustness of the two-dimensional carbon nanostructure. Even with extreme deformation, excellent carrier mobility in monolayer Graphene can be preserved.
“Graphene is 200 times stronger than steel according to The University of Manchester.”
2. Conductivity:
Graphene is a zero-gap semiconductor, because its conduction and valence band meet at the Dirac points, which is shown in figure above. It can conduct electricity better than silver (40% more conductive than silver).
3. Thermal conductivity:
Graphene is a perfect thermal conductor. Its thermal conductivity is much higher than all the other carbon structures. Graphite has thermal conductivity 5 times smaller than graphene. That is not only faster but also better at dissipating heat.
4. Flexibility:
Graphene is highly flexible material and can stretch up to 20% of its original length. So, it can replace Indium-tin oxide which is currently used for touch screens as it conducts well but it is brittle.
5 Optical Properties:
Graphene is so thin that it only absorb 2% of light fall on it and 98% passes through it and the reason behind this transparency is unusual low energy structure of monolayer Graphene and zero band gab between conduction band and valence band.
APPLICATIONS:-
1. Composite and Coatings:
By combining graphene with paint, a unique graphene coating is formed. This could signal the end of the deterioration of ships and cars through rust. A graphene-based composite aircraft wing could drastically decrease weight. This could result in the world’s lightest, strongest, safest, greenest plane.
2. Bio-Medical:
Applications in targeted drug delivery, improved brain penetration. In Cancer treatment, Graphene is allowing to act as effective transporter of drugs to the body which reduces the effects of more invasive remedies such as chemotherapy.
3. Graphene in form of Membranes:
It is a perfect barrier when dealing with liquids and gasses. It can separate organic solvent and gas mixture from water. The removal of harmful carbon dioxide released into the atmosphere by power stations is not currently done on any scale, graphene membranes could change that.
So, graphene has a huge potential in the field of nanotechnology and many researches are going on to make graphene based devices for commercial use.
This article is contributed by Pinki.
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