GRAPHENE AND ITS FUTURE

APPLICATIONS

BY: ARPIT AGARWAL

ELECTRICAL & ELECTRONICS (3RD YEAR)

1109721026

UNDER GUIDANCE OF:Mr MANISH SRIVASTAVA

GRAPHENE: Structural Properties* Hexagonal structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes and fullerenes

* Graphite (layered material) formed by stacks 41 of graphene sheets separated by 0.3 nm and held together by weak vander Waals forces.

* Each atom forming 3 bonds with each of its nearest neighbors, known as the sigma bonds.

* Fourth valence electron is in the 2pz state oriented perpendicular to the sheet of graphite forms a conducting sigma bond.

* Two dimensional sp2 hybridized forms of carbon

* Zero band gap semiconductor with 2 linearly dispersing bands that touch at the corners of the first Brillouin zone.

a) Fullerene b) Nanotubec) Graphite

Honey comb structure of Graphene

GRAPHENE: DiscoveryFor decades but until recently there were no experiments on grapheme,Due to the difficulty in separating and isolating single layers of graphene for study.

In 2004, Andre Geim and Kostya Novolselov came up with an ingenious method after years of effort to isolate monolayer graphene flakes. Andre and Kostya were awarded the 2010 Nobel prize in physics for this work.

At University of Manchester in England, they simply stuck a flake of graphite debris onto plastic adhesive tape, folded the sticky side of the tape over the flake and then pulled the tape apart, cleaving the flake in two. As the experimenters repeated the process, the resulting fragments grew thinner

Andre Geim

Kostya Novoselov

GRAPHENE: SynthesisTwo basic techniques used are :1)To cleave multi layer graphite into single layers. (EXFOLIATION)2) By depositing one layer of Carbon onto another material (EPITAXY)

a) DRAWING METHODThe basic ‘recipe’ for making graphene using “scotch tape” technique requires using 300nm of SiO2-coated silicon wafer as a substrate and cleaning it with a mix of hydrochloric acid and hydrogen peroxide To remove any residue that is adhering to the wafer. Following this one patiently peels graphite by sandwiching it between scotch tape repeatedly till the tape is translucent.

b) GRAPHITE OXIDE REDUCTIONGraphite can be oxidized to produced GO and then exfoliated to create stable aqueous dispersions of individual sheets. After deposition, GO may be reduced to graphene either chemically or by means of thermal annealing

EXFOLIATION

Graphene layer formed using Scotch tape

Graphite oxideexfoliated in water as individual platelets of Graphene oxide

EPITAXYa) SONICATIONApplying a layer of graphite oxide film to a DVD and burning it in a DVD writer produced a thin graphene film with high electrical conductivity and specific surface area that was highly resistant and malleable

c) METAL SUBSTRATE EPITAXYCopperthis technique employs copper foil; at very low pressure, the growth of graphene automatically stops after a single graphene layer formsNickelHigh-quality sheets of few-layer graphene exceeding 1 cm2 (0.2 sq in)in area have been synthesized via chemical vapor deposition on thin nickelfilms with methane as a carbon source.

b) SILLIOCN CARBIDE EPITAXYHeating silicon carbide (SiC) to high temperatures (>1100 °C)under low pressures (~10−6 torr) reduces it to graphene.

GRAPHENE: CharacteristicsELECTRONIC PROPERTIES* High Electron Mobility at room temperature, with reported values in excess of 15,000 cm2/Vs.* Intrinsic graphene is a semi-metal or zero-gap semiconductor* Low resistivity and better current capacity & temperature conductivity* Graphene is estimated to operate at terahertzfrequencies i.e. trillions of operations per second.

OPTICAL PROPERTIES* An unexpectedly high opacity for an atomic monolayer, it absorbs πα= 2.3% of white light, where α is the fine-structure constant.* Graphene can be saturated readily under strong excitation over the visible to near-infrared region, due to the universal optical absorption

MECHANICAL PROPERITIES* Strongest materials ever tested* Breaking strength 200 times greater than steel, a bulk strength of130GPa.

FUTURE APPLICATIONSGraphene amazing properties brings scope of various future applications in followingFields:

* Biological Engineering* Optical Electronics* Ultra Filtration* Composite Materials* Photovoltaic Cells* Super Capacitors

BIOLOGICAL ENGINEERINGGraphene Advantages* Large Surface Area* High Electrical Conductivity* Thinness and Strength

Uses* Efficient Bioelectric Sensory Devices* Able to monitor Glucose level, cholesterol DNA sequencing, Haemoglobin level etc* Toxic Graphene as anti-cancer treatment* Process of Tissue Regenration

OPTICAL ELECTRONICS

Graphene Advantages* Optically transmit more than 90% of light* Conductivity more than 1x 106 Ω1m1* Completely Transparent material* High Tensile strength and Flexible* Able to replace Indium Tin Oxide (ITO) due to less cost and better properties

Uses* Touchscreens* Liquid Crystal Display (LCD)* Organic Light Emitting Diodes (OLEDs)

LCD, Touchscreen, OLEDs Schematics

PHOTOVOLTAIC CELLSCurrently: silicon wafers, thin films

Graphene Advantages* Transparent conducting electrode* Robust, conductive, abundant* Cheaper than ITO* Enhanced light trapping* Efficient charge transport (1D)

A new design:* Layer of graphene (transparent cathode)* Conductive polymer (maintains integrity)* ZnO nanowire layer (electron transport)* PbS quantum dots (hole transport)* Au layer (anode)

* 4.2% conversion efficiency (5.1% for ITO)* Cheaper to produce

SUPER CAPACITORS

Graphene Advantages* High surface area to weight ratio (2600 m2 /g)* High conductivity* Measured specific capacitance 135 F/g

Uses* Electric vehicles* Backup powering* High power capability* Cell phones

ULTRA/SUPER CAPACITORS100 years old technology enhanced bymodern materials based on polarization ofelectrolytes, high surface area electrodesand extremely small charge seperation

ECDL (Electro Chemical Double Layer) Capacitor

Super Capacitor Model

REFERENCES* A.K. Geim and K.S. Novoselov- The Rise of Graphene, 2007. Nature Material.

* C. N. R. Rao, K. S. Subrahmanyam, H. S. S. Ramakrishna Matte and A. Govindaraj Chemistry and Physics of Materials Unit, International Centre for Materials Science, New Chemistry Unit and CSIR Centre of Excellence in Chemistry

* Andrea C. Ferrari Department of Engineering, Cambridge University, Cambridge, UK http://cape.eng.cam.ac.uk/

* Rodney S. Rodney S. Ruoff Ruoff ,The University of Texas at Austin http://bucky--central.me.utexas.edu/

* www.en.wikipedia.org