Graphene – The thinnest strongest material in nature
Essay code B3
Carbon is the elementary constituent of organic chemistry and it plays a huge role in the
existence of life. This element is important because it may function as conductors, semiconductors, as well as insulators. Carbon’s ability to form sp2 covalent bonds contributes to its
ability to form strong networks and the strong bonds found in crystalline forms, such as
diamond. Allotropes of carbon can be found in nano scale dimensions such as fullerene,
grapheme, graphite, etc. Carbon allotropes have better stabilities due to its high activation
barrier caused by their structural arrangements. They are considered significant because of their
unique physical and chemical properties. Nano scale carbon was observed in zero dimensions,
one dimension, and three dimensions as fullerene, nano tube, and graphite and diamond
respectively. However, two professors from the University of Manchester in England,
Konstantin Novoselov and Andre Geim won the Nobel Prize in physics for extracting the two
dimensional nano scale carbon, known as grapheme (thick single layer sheet of sp2 hybridized
carbon atoms) and graphite (formed by stacking many grapheme sheets usually found in lead
pencils). Graphene is considered to be the thinnest of all materials. During the experiment,
Novoselov and Geim extracted grapheme and graphite by using adhesive scotch tape in 2004.
The unique mechanical, physical, quantum, and thermal properties make grapheme one of the
most demanded materials on earth today because of its stability in non-functionalized form.
Graphene is extremely flexible and can be considered as the building block for other nano scale
carbon forms. It can be rolled to form one dimensional nano tube, wrapped to form a zero
dimensional fullerene, and it can be stacked in multiple layers to form three-dimensional
graphite.
Graphene is a one atom thick sheet with a single layer formation of sp2 hybridized
carbon atoms. Electron diffraction patterns obtained from studying the structure of grapheme
using transmission electron microscopy indicates graphene’s honeycomb lattice in a hexagonal
array. When grapheme is bombarded with carbon atoms, it can rearrange itself into a hexagonal
molecule. The properties of two-dimensional graphene are different than three-dimensional
graphite in many ways.
The use of adhesive tape and a pencil lead the way to the synthesis of grapheme. Today,
graphene can be synthesized by micromechanical exfoliation, chemical vapor disposition on the
on a single crystal metal such as nickel, chemical synthesis from graphite, reduction of graphene
oxide sheets, and chemical exfoliation. Graphene can be cleaved micromechanically by peeling
a highly oriented pyrolitic graphite using scotch tape and attaching it to a silicon substrate,
known as a top-down approach. The reduction of Graphene oxide to obtain graphene is possible
by removal of functional groups by chemical reduction to make it highly hydrophilic. The
reducing agents that are used are hydroquinone, dimethyl hydrazine, hydrazine hydrate. Other
types of reduction include electrostatic reduction, thermo reduction and photo catalytic
reduction.
The physical properties of Graphene is very significant because of its better conductivity
and stability. The carbon-carbon bond length in graphene is 0.142 nanometers. Even though
graphene is strong and stable, the stacking of graphene to form graphite is held together by weak
Vander Waals forces. Therefore graphite is the softest material available on earth. Due to its
immense stability, Graphene can hold materials six order of magnitudes higher than that of
copper. The extraordinary chemical and thermal properties of graphene are due to several
factors. It is a chemically inert molecule. In the delocalized orbitals, electrons are free to move
and therefore suffer very little energy dissipation and there is no energy gap. The electrons in
graphene also move at a regular speed. It has a higher electron mobility at room temperature
compared to other semiconductors. This is independent of their kinetic energy. Graphene is a
high heat conductor and this helps to prevent the thermal management and heat dissipation issue
of the high speed integrated density chips. Even when graphene is not functional, it remains
highly stable and conductive when it is entered into other nano material devices. Graphene sheet
is thermodynamically unstable if its size is less than about 20 nm.
Graphene is a hundred times stronger than steel. One thin layer of graphene can hold an
elephant. It has been tested that graphene breaks at a hundred times stronger than the strength at
which steel breaks. This was proven by probing a diamond into a thin layer of graphene until it
broke. Graphene is very stretchable. It can stretch up to 20 percent of its length and is also
transparent in color and conducts electricity better than copper. There is no band gap in graphene
and therefore it is used in photovoltaic cells because every energy frequency can be absorbed by
graphene. All the photons at different frequency are then converted to electrons. The tensile
strength of graphene is remarkable because of its strongest bonds among all atoms.
The chemical properties of Graphene is unique because both the sides of the 2D structure
can be exposed to chemical reactions. The carbon atoms at the tip of the graphene sheets have
extra chemical reactivity than compared to other Carbon nano scale materials such as nano tubes.
Carbon can react with oxygen gas at less than 260 °C and graphene can burn at 350 °C.
Graphene can be considered as the chemically most reactive form of carbon because of its
honeycomb lattice like hexagonal arrangement. The structural analysis of graphene is often
conducted using NMR and IR spectroscopy by modifying it with functional groups. The thermal
properties of Graphene include conductivity at room temperature measured. 12C has a better
conductivity than the 50:50 isotope ratio. Even though graphene can be rolled into a nano tube, it
is less stable at this structure. The mechanical strength of Graphene was illustrated using 1
square meter graphene which supports a 4kg cat and will weigh up to one cat whisker. The
spring constant value of graphene was 1-5 N/m and the stiffness was 0.5 TPa.
The major uses and applications of graphene composites, energy storage devices, include
terahertz imaging, sensors, transistors, membranes, batteries, thin coating for solar cells, digital
and LCD displays. Due to its high tensile strength and because of the fact that graphene would
not crack upon bending, graphene can be used to replace indium tin oxide which is used for the
transparent layer of computers and phones. Graphene can be used in the new super capacitors
which store very large amounts of power due to its extraordinary high area to volume ratio. The
transistors that are made from carbon can be faster than the silicon chips used today because of
its high electrical conductivity. Due to all the unique properties mentioned above, graphene can
be used in digital displays such as phone and computer, flexible electronic devices and
composite materials. Because graphene is a good semiconductor and metal, it can be used to
replace silicon chips and thus impact highly defined applications such as high speed computer
chips and biochemical sensors. Due to graphene’s better conductivity, it can replace copper in
future computer chips.
Because of graphene’s high heat conducting property, ne of the major uses of graphene is
to minimize over heating by efficient thermal management of high speed high integration density
chips. The increasing power densities of chips create a major issue of inefficient heat removal. It
can be properly managed to remove heat efficiently and spread the heat out in future integrated
circuit chips. Solar cells must be efficiently removed of heat in order to function properly and
generate heat. The high electron mobility at room temperature will help ballistic conduction
possible by having high nano electric devices such as ballistic transistors. The interconnection
between chips is possible due to the high electron mobility of graphene. The high spring constant
and stiffness value of graphene would help if used in applications such pressure sensors and
resonators.
Carbon can be functionalized in a chemical and biological manner to produce
opportunities in a variety of fields. The covalent modification can be altered to produce change
in properties because of its strong delicate thin layer. One of the methods to change graphene
functionally without changing its inherent properties is by using bio recognition molecules. This
is possible by attaching avidin, biotin, peptides, nucleic acids, proteins, aptamers, small
molecules, bacteria by physical adsorption or chemical conjugation. Also to introduce catalytic
properties, graphene can be functionalized into hybrids such nano particle. Thus by synthesizing
these hybrids, graphene is used as bio sensors. For example an inorganic graphene hybrid such
as gold graphene has been showing exceptional properties better than individual constituents.
This is synthesized by spontaneous reduction of gold ions and layer by layer filling of alternate
graphene and gold. In the field of medicine, graphene has improved PCR results by reducing the
number of cycles to 65% and increasing the yield of DNA product due to its high thermal
conductivity. Graphene is also being used as frequency multiplier when an incoming frequency
was used to produce multiple outgoing same frequencies. Graphene quantum dots can be used in
applications such as electronics, opt electrics and electro magnetics. It is an excellent source of
microbial detection due to its small atomic thickness and large surface area.
The potential applications of graphene are also highly remarkable. Because of its high
flexibility, graphene can be expected to lead to building of a new type of cell phones which can
be rolled into thin layers behind the ear, HD televisions with the thickness of wallpaper,
electronic devices which the users can fold and wrap into a tiny square. Improved results in
desalination has also been tested using graphene to yield better results. Graphene could be
practically used for single molecule gas detection because it is a good sensor due to its 2D
structure and exposure to chemical reaction on both sides. This makes it easier to sense adsorbent
molecules.