GRAPHENe

It’s Story….

WHAT GRAPHENE IS?

• It is all started with structure of graphite solved in 1916 –powder diffraction.• In 1924 -single crystal diffraction.•Comes in focus in 2010 when

‘For the Groundbreaking experiments regarding two dimensional material Graphene’

Electron microscopic image on Sio2 surface

THE GRAPHENE

Introduction

Graphene can be described as a one-atom thick layer of graphite.

It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes.

Graphene is the strongest, thinnest material known to exist. Graphene is an atomic-scale

honeycomb lattice made of carbon atoms.

Graphene is a 2D crystal of carbon atoms, arranged in a honeycomb lattice

Each carbon atom is sp2

hybridized and it is bound to its three neighbors.

History

One of the very first patents pertaining to the production of graphene was filed in October, 2002 entitled, "Nano-scaled Graphene Plates“.

Two years later, in 2004 Andre Geim and Kostya Novoselov at University of Manchester extracted single-atom-thick crystallites from bulk graphite

Geim and Novoselov received several awards for their pioneering research on graphene, notably the 2010 Nobel Prize in Physics.

Structure

Graphene is a 2-dimensional network of carbon atoms.

These carbon atoms are bound within the plane by strong bonds into a honeycomb array comprised of six-membered rings.

By stacking of these layers on top of each other, the well known 3-dimensional graphite crystal is formed.

It is a basic building block for graphitic materials of all other dimensionalities.

It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite.

Thus, graphene is nothing else than a single graphite layer.

Sheets of graphene are bonded by loose bond in graphite. These bonds are broken and sheets are isolated to form graphene. These isolated hexagonal sheets are graphene.

STRUCTURE OF GRAPHENE

STRUCTURE

It is the one-atom thick planar sheet of carbon atoms (graphite), which makes it the thinnest material ever discovered.

2-dimentional crystalline allotrope of carbon.

C-C Bond length is 0.142 nm.

Graphene Sheets interplanar spacing is of 0.335 nm.

It is almost completely transparent, yet so dense that not even helium can pass through it.

Andre Geim and Kostya Novoselov pulled graphene layers from graphite and transferred them onto thin SiO2 on a silicon wafer in a process called either micromechanical cleavage or the Scotch tape technique.

Graphene can be seen with help of

1.Transmission electron microscopy.

2.Electron microscopy

3.Optical microscope

STRUCTURE……

Graphene can self-repair holes in its sheets, when exposed to molecules containing carbon, such as hydrocarbons. Bombarded with pure carbon atoms, the atoms perfectly align into hexagons, completely filling the holes.

STRUCTURAL

PROPERTIES OF GRAPHENE.

• The flat graphene sheet is unstable with respect to scrolling i.e. bending into a cylindrical shape

• As of 2009, graphene appeared to be one of the strongest materials known with a breaking strength over 100 times greater than a hypothetical steel film of the same (thin) thickness, with a Young's modulus (stiffness) of 1 TPa (150000000 psi).

• 1 square meter graphene hammock would support a 4 kg cat but would weigh only as much as one of the cat's whiskers, at 0.77 mg (about 0.001% of the weight of 1 m2 of paper)

MECHANICAL

Physical properties of Graphene

Density- density of graphene 0.77 mg/m2.

Z

Strength- With its breaking strength 42 N/m it is 1000 times stronger

than steel

Optical transparency- graphene is almost

transparent with its ability of absorb just 2.3% of light

falling on it.

Thinnest possible material

Mechanical Properties

To calculate the strength of graphene, scientists used a technique called Atomic Force Microscopy.

It was found that graphene is harder than diamond and about 300 times harder than steel.

The tensile strength of graphene exceeds 1 TPa.

It is stretchable up to 20% of its initial length.

1.MECHANICAL EXFOLIATION : This involves splitting single layers of graphene from multi-layered graphite. Achieving single layers typically requires multiple exfoliation steps, each producing a slice with fewer layers, until only one remains. Geim and Novosolev used adhesive tape to split the layers.

SOME PRODUCTION METHODS

2. EPITAXY : Epitaxy refers to the deposition of a

crystalline overlayer on a crystalline substrate and the graphene–substrate interaction can be further passivated

•In some cases epitaxial graphene layers are coupled to surfaces weakly enough (by Van der Waals forces)

Sicilicon-based epitaxy technology for producing large pieces of graphene with the best quality to date

EPITAXY EXAMPLES :

• Silicon carbide

• Metal substrates

• Copper Vapor Deposition ( CVD)

3. REDUCTION OF GRAPHITE OXIDE

4. METAL CARBON MELT

5. SOLVENT EXFOLIATION

6. CARBON DIOXIDE REDUCTION

7. NANOTUBE SLICING

FIG METAL CARBON MELT

Graphene Based Composites For Future Applications

Outline

Types of graphene based composites

Useful properties of graphene in composites

Potential applications of various types of graphhene composites

Graphene Based Composites (1)

Polymer-Graphene Composites

Metal-Graphene Composites

Ceramic-Graphene Composites

Graphene Based Composites (2)

Coating/Film/Paper Form

Sandwich Form

Bulk form

Useful Properties of Graphene in Composites

Functional (e.g., Electrical) properties

Thermal properties

Mechanical properties

+ Lightweight, unique morphology, chemical stability.

Graphene Reinforced Composites

Mechanical properties:

1) Stiffest (E > 1 Tpa),

2) Strength: >100-GPa tensile strength (40 times >

steel).

Morphology: 2D shape

Ideal reinforcement phases to make stronger and

tougher composites for various applications

Chemical Properties

Graphene is chemically the most reactive form of carbon.

Only form of carbon (and generally all solid materials) in which each single atom is in exposure for chemical reaction from two sides (due to the 2D structure).

Carbon atoms at the edge of graphene sheets have special chemical reactivity.

graphene burns at very low temperature (e.g., 350 °C).

Graphene has the highest ratio of edgy carbons (in comparison with similar materials such as carbon nanotubes).

Graphene is commonly modified with oxygen- and nitrogen-containing functional groups

Electronic Properties

It is a zero-overlap semimetal (with both holes and electrons as charge carriers) with very high electrical conductivity.

Electrons are able to flow through graphene more easily than through even copper.

The electrons travel through the graphene sheet as if they carry no mass, as fast as just one hundredth that of the speed of light.

High charge carrier mobility, for which values of 10,000 cm2/Vs, in some cases even 200,000 cm2/Vs were reported.

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Thermal Properties

Graphene is a perfect thermal conductor

Its thermal conductivity is much higher than all the other carbon structures as carbon nanotubes, graphite and diamond (> 5000 W/m/K) at room temperature

Graphite, the 3 D version of graphene, shows a thermal conductivity about 5 times smaller (1000 W/m/K)

The ballistic thermal conductance of graphene is isotropic, i.e. same in all directions

ApplicationsWhile as of 2014, graphene is not used in commercial applications, many have been proposed and/or are under active development, in areas including electronics, biological engineering, filtration, lightweight/ strong composite materials, photovoltaics and energy storage.

Other Applications

Graphene nanoribbons

IR detectors

Single-molecule gas detection

Piezoelectric materials

Energy Harvesting

Composite Materials

Liquid Cells for Electron Microscopy

Thermal management materials

Optical Modulators

Chemical sensors

Its a Wonder material that could revolutionize the world