Friday, 12 August 2016

Amazing 2-D Material - Graphene

Ms Pranati Purohit
Asst Professor
The NorthCap University, Gurgaon

Discovery of two-dimensional single atomic layer thick material has baffled scientists who never imagined that such a material could exist. In 2004 physicists,KS Novoselov, AK Geim and their colleagues first accidently made the Nobel prize winning discovery of this new wonder material in the peelings of the scotch tape, which was being used to clean the graphite surface. This one-atom thick material showed miraculous and confounding properties viz. 200 times stronger than steel, more conducting than silver, 98% transparent to light (yet it is visible to naked eye), impermeable to even the lightest hydrogen gas, easily amenable to modification in its properties. Its unsurpassed transparency and conductance can potentially replace the electrodes in touchscreens and solar cells. Further, the extremely high strength to weight ratio can integrate it into composite materials for lightning proof aircraft fuselages. Being impermeable would make it perfect to use in hydrogen reservoirs.

Isolation
 
At present, the most popular approaches to graphene isolation are electrochemical exfoliation. In one experiment the researchers have been able to produce approximately 16.3 g of graphene (area of about 16 football fields) in 30 minutes using graphite and Pt electrodes in an ammonium salt electrochemical bath.Exfoliation is not suited to the electronics industry. Growth on metals and subsequent transfer to insulating substrates, and thermal decomposition of SiC to produce so called epitaxial graphene on top of SiC wafers have the potential for producing wafer-scale graphene.


Electronic properties

Graphene exhibits a variety of transport phenomena that are characteristic of 2D Dirac fermions, such as specific integer and fractional quantum Hall effects, a ‘minimum’ conductivity of ~4e2/h even when the carrier concentration tends to zero.Suspended samples of graphene show mobility (μ) of up to 106 cm2 V-1 s-1. It also shows near-ballistic transport at room temperature. Large-area graphene is a semimetal with zero bandgap. Its valence and conduction bands are cone-shaped and meet at the K points of the Brillouin zone. Due to zero bandgap, graphene cannot be configured in a switch and hence is not suitable for logic applications unless its band structure isopened. This has become possible in a number of ways: by constraining large-area 2-D graphene in one dimension to form graphene nanoribbons, by biasing bilayer grapheneand by applying strain to graphene. Graphene has been made luminescent by chemical and physical treatments to produce quantum dots. Graphene has plasmonic excitations in terahertz and mid-infrared and has emerged as a unique material for electronic applications in this frequency range such as THz lasers, amplifiers, detectors, etc.

Applications

Graphene has changed from being the exclusive domain of condensed matter physicists to being explored by electron-device community. In particular, graphene-based transistors have developed rapidly and are now considered an option for post-silicon electronics. Graphene is considered as an ideal material for energy storage and conversion. During the past several years, a variety of graphene based materials (GBMs) have been successfully prepared and applied in super-capacitors, lithium ion batteries, water-splitting, electrocatalysts for fuel shells and solar cells. As graphene is a conductive yet transparent material, with low cost and low environmental impact, it is an ideal material for manufacture of sensors and biosensor-based devices in various transduction modes, from electrical and electrochemical transduction to optical transduction.

Industry giant IBM has produced several electronic component prototypes. Flat screens (70cm in the diagonal) with graphene electrodes, tennis rackets made with graphene have been championed by some industries.

Conclusion and outlook

The speed of development in graphene products in the last ten years is much faster than the typical 40years it takes for a new material to move from an academic lab into a consumer product. Governments and industries around the world have earmarked billions of dollars on research and development of graphene products. It would not be out of place to say graphene as the fastest developing material known so far.According to recent reports on thefuture of graphene, a market worth $1.5bn in 2015 and $7.5bn in 2025 is forecasted.

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