GRAPHENE A MIRACLE MATERIAL

BY ENGR . AGBADUA SEGUN

                                                     ABSTRACT

The paper tends to look at the origin , production and relevance of Graphene to the material world.

                                                                      INTRODUCTION

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp²-bonded carbon atoms that are densely packed in a honeycomb crystal lattice.

The carbon-carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of 0.335 nm, which means that a stack of 3 million sheets would be only one millimeter thick. Graphene is the basic structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons.

 METHODS OF PRODUCING OF GRAPHENE

Growth from metal-carbon melts

Pyrolysis of sodium ethoxide

Sugar

Epitaxial growth on metal substrates

Graphite oxide reduction

Epitaxial growth on silicon carbide

Graphite oxide Reduction

Graphite oxide exfoliation can be achieved by rapid heating and yields highly dispersed carbon powder with few percents of graphene flakes. Reduction of graphite oxide monolayer films

 Growth from metal-carbon melts

The general idea in this process is to dissolve carbon atoms inside a transition metal melt at a certain temperature, and then allowing the dissolved carbon to precipitate out at lower temperatures as single layer graphene.

Epitaxial growth on silicon carbide

 This process produces epitaxial graphene with dimensions dependent upon the size of the SiC substrate (wafer). The face of the SiC used for graphene formation, silicon- or carbon-terminated, highly influences the thickness, mobility and carrier density of the graphene.

From sugar

Sucrose is turned quickly and easily into graphene with the help of  copper or nickel substrate and  subjected to 800 °C under low pressure with exposure to argon and hydrogen gas.

graphene is an isolated atomic plane of graphite. Graphene has been known since the invention of X-ray crystallography. Graphene planes become even better separated in intercalated graphite compounds. Graphene films were produced by chemical vapor deposition and used as anodes for application in photovoltaic devices. Tiny fragments of graphene sheets are produced whenever graphite is abraded, such as when drawing a line with a pencil

MECHANICAL PROPERTIES

Graphene appears to be one of the strongest materials ever tested. Measurements have shown that it  has a breaking strength 200 times greater than steel, with a tensile strength of 130GPa (19,000,000 psi).^[116] However, the process of separating it from graphite, where it occurs naturally. Not only is it lighter, stronger, harder and more flexible than steel, it is also a recyclable and sustainably manufacturable product that is eco-friendly and cost effective in its use.

aerospace companies such as Boeing have already started to replace metals with carbon fibres and carbon-based materials, and graphene paper with its incomparable mechanical properties would be the next material for them to explore.

Thermal properties

The ballistic thermal conductance of graphene is isotropic.^[111] The Potential for this high conductivity can be seen by considering graphite, a 3D version of graphene that has basal plane thermal conductivity of over a 1000 Wm⁻¹K⁻¹ (comparable to diamond). In graphite, the c-axis (out of plane) thermal conductivity is over a factor of ~100 smaller due to the weak binding forces between basal planes as well as the larger lattice spacing

Integrated circuits

Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a FET. The issue is that single sheets of graphene are hard to produce, and even harder to make on top of an appropriate substrate, graphene was epitaxially grown on SiC in a quantity and with quality suitable for mass production of integrated circuits. The circuit handled frequencies up to 10 GHz, and its performance was unaffected by temperatures up to 127C

Electrochromic devices

Graphene Oxide can be reversibly reduced and oxidized using electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer graphene oxide films are shown to result in switching between partially reduced graphene oxide and graphene, a process which modifies the electronic and optical properties

Transparent conducting electrodes

Graphene's high electrical conductivity and high optical transparency make it a candidate for transparent conducting electrodes, required for such applications as touchscreens, liquid crystal displays

Organic light-emitting diodes (OLEDs) with graphene anodes have also been demonstrated. The electronic and optical performance of devices based on graphene are shown to be similar to devices made with indium-tin-oxide.

Graphene biodevices

Graphene's modifiable chemistry, large surface area, atomic thickness and molecularly-gatable structure make antibody-functionalized graphene sheets excellent candidates for mammalian and microbial detection and diagnosis devices.

The most ambitious biological application of graphene is for rapid, inexpensive electronic DNA sequencing. Integration of graphene (thickness of 0.34 nm) layers as nanoelectrodes into a nanopore can solve one of the bottleneck issues of nanopore-based single-molecule DNA sequencing

Anti-bacterial

The Chinese Academy of Sciences has found that sheets of graphene oxide are highly effective at killing bacteria such as Escherichia coli. This means graphene could be useful in applications such as hygiene products or packaging that will help keep food fresh for longer

CONCLUSION

Graphene has taken over from the silicon and germanium etc , that are doping materials.

It has shown how invaluable carbon is to the Engineering world.