Graphene
Graphene is the name for an atomic
thick honeycomb sheet of carbon atoms. It is a component of other graphite
materials. Harder than diamond, but harder than rubber. It is stronger than
steel but lighter than aluminum. Graphene is the most powerful known material.
Its high electron mobility is 100
times faster than silicon. It has twice the thermal conductivity of the diamond.
The conductivity is 13 times that of copper. It absorbs only 2.3% of the
reflected light. Due to its impermeability, even the smallest atoms (helium)
cannot pass through a defect-free single-layer graphene sheet. A surface area
of 2630 square meters/gram means that
less than 3 grams can cover the entire soccer field.
Graphene is the basic building block
of other graphite materials. It is also a conceptually new class of materials,
so-called two-dimensional (2D) materials with only one atom in thickness.
Graphene is also very attractive for the fabrication of mixed-dimensional van der Waals heterostructures that can be
performed by hybridizing graphene with 0D quantum dots or nanoparticles, 1D
nanostructures such as nanowires and carbon nanotubes, or 3D bulk materials.
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Properties of Graphene
Electrical Properties
One of the reasons why
nanotechnology researchers working towards molecular electronics are so excited
about graphene is its electronic properties. It is one of the best conductors
on earth. The unique atomic arrangement of carbon atoms in graphene allows
electrons to move very fast and easily without significantly increasing the chances
of scattering them, saving valuable energy normally lost in other conductors.
Scientists have discovered that
graphene is capable of conducting electricity even at a nominally zero carrier
concentration limit because electrons do not appear to slow down or localize.
Electrons traveling around the carbon atom interact with the periodic potential
of the graphene honeycomb lattice. This creates new quasiparticles that have
lost their mass or rest mass. In other words, the conduction of graphene does
not stop. We also found that they move much faster than the electrons in other
semiconductors.
Mechanical Properties
The striking and unique mechanical
properties of graphene, its stiffness, strength, and toughness are one of the
reasons why graphene stands out as an individual material and as a reinforcing
agent in composites. They occur due to the stability of sp2 bonds that form a
hexagonal lattice and resist various in-plane deformations.
Hardness
The fracture forces obtained from
the experiments and simulations were almost the same, and the experimental The value of the second elastic stiffness was 340 ± 50 N m-1. This value
corresponds to Young's modulus of 1.0 ± 0.1 TPA, assuming an effective
thickness of 0.335 nm.
Strength
Defect-free monolayer graphene is
considered to be the strongest material ever tested at a strength of 42 N m-1.
This corresponds to an intrinsic strength of 130 GPa.
Toughness
Fracture toughness, a property
highly relevant to engineering applications is one of the most important mechanical
properties of graphene, measured as a critical stress intensity factor of 4.0 ±
0.6 MPa.
Applications of Graphene
Energy Storage and Solar Cells
Graphene-based nanomaterials have
many promising applications in energy-related fields. Some recent examples:
Graphene improves both the energy capacity and charge rate of rechargeable
batteries. Activated graphene makes supercapacitors with excellent energy
storage. Graphene electrodes could lead to a promising approach to making cheap,
lightweight, and flexible solar cells. Multi-functional graphene mats are
promising substrates for catalytic systems.
The researchers also discovered an important and unexpected relationship between the chemical/structural defects
of graphene as a host material for electrodes and its ability to suppress
dendrite growth. Batteries can cause electrical short circuits, overheating, and
fire.
Due to the excellent transport
properties of electrons and very high carrier mobility, direct bandgap
monounsaturated materials such as graphene and other transfer metal
decalcogenides and black phosphorus can be used in low cost, flexible and
highly efficient photovoltaic devices. It shows great potential. They are the
most promising materials for advanced solar cells.
Sensor Applications
Functionalized graphene holds great
promise for biological and chemical sensors. Already, researchers have shown
that by combining the characteristic 2D structure of graphene oxide with super permeability to water molecules, devices can be detected at unprecedented
rates.
Scientists have discovered that
chemical vapors alter the noise orbits of graphene transistors, activating the
selective gas sensing of many vapors in a device made of pure graphene. The
graphene surface does not need to be activated.
A rather cool approach is to connect
passive wireless graphene nanosensors to biomaterials via silk bioabsorption,
as shown by tooth graphene nanosensor tattoos monitoring oral bacteria.
Researchers have also begun to use
graphene foam, a three-dimensional structure of interconnected graphene sheets,
very highly conductive. These structures hold great promise as gas sensors and
biosensors for disease detection.
Electronics Applications
Graphene has a unique combination of
properties such as mechanical flexibility, high electrical conductivity and
chemical stability, ideal for next-generation electronics. Combining this with
inkjet printing gives you a cheap and scalable path to harness these properties
in real-world technology.
Transistor and Memory
Some of the most promising
applications for graphene are electronics, detectors, and thermal management.
The first graphene field-effect transistors-both bottom and top gate-have
already been demonstrated. At the same time, the level of electronic low-frequency noise must be reduced to acceptable levels in order for the
transistor to be useful in analog communication or digital applications.
Graphene-based transistors are
considered to be potential successors to some of the silicon components
currently in use. The fact that electrons can travel faster through graphene
than through silicon indicates the potential for this material for terahertz
computing.
In the ultimate nanoscale transistor, electrons avoid collisions. That is, the
current flow is virtually unobstructed. Ballistic conduction enables incredibly
fast switching devices. Graphene has the potential to achieve ballistic
transistors at room temperature.
Graphene has the potential to
revolutionize electronics and replace the silicon materials used today, but
with the Achilles heel. Pristine graphene is a semimetal and lacks the bandgap
needed to function as a transistor. Therefore, it is necessary to design the
band gap of graphene.
Experiments have demonstrated the
benefits of graphene as a platform for flash memory, demonstrating that it may
exceed the performance of current flash memory technology by taking advantage
of the intrinsic properties of graphene.
Flexible and Elastic Foldable Electronics
Flexible electronics rely on
bendable substrates and truly collapsible electronics require a foldable substrate with very stable conductors that can withstand folding.
That is, in addition to a foldable
substrate such as paper, the conductors deposited on this substrate must also
be foldable. To that end, researchers have demonstrated a manufacturing process
for folding graphene circuits based on paper substrates.
Graphene's excellent conductivity,
strength and elasticity make it possible to create circuits on flexible
plastic substrates for applications such as stretchable electronics.
Scientists have devised a chemical
vapor deposition (CVD) method to turn graphene sheets into porous,
three-dimensional foams with extremely high conductivity. By impregnating this
foam with a siloxane-based polymer, researchers have made a composite material
that can be twisted, stretched, and bent without compromising it's electrical or
mechanical properties.
Photo Detector
Researchers have demonstrated that
graphene can be used in telecommunications applications, and that it's weak, the universal optical response can translate into advantages for ultrafast
photonics applications. They also found that graphene could potentially be used
as a saturable absorber with a wide range of optical responses from
ultraviolet, visible, infrared to terahertz.
The use of graphene for
optoelectronics applications are of great research interest. Graphene-based
photodetectors have been realized previously and graphene's suitability for
high bandwidth photodetection has been demonstrated at 10 GBit / s optical data
links.
One new approach is based on the
integration of graphene into optical microcavities. Increasing the electric
field amplitude inside the cavity absorbs more energy and significantly
increases the optical response.
Coating
Coating objects with graphene can be
used for a variety of purposes. For example, researchers have shown that
graphene sheets can be used to create superhydrophobic coating materials that
exhibit stable superhydrophobicity under both static and dynamic conditions,
thereby forming highly water-repellent structures.
Graphene is also the world's
thinnest known coating to protect metals from corrosion. It has been found that
graphene, whether made directly on copper or nickel or transferred to another
metal, provides protection against corrosion.
Researchers have demonstrated the
use of graphene as a transparent conductive coating for photonic devices,
demonstrating that its high transparency and low resistivity make this
two-dimensional crystal ideal for electrodes in liquid crystal devices (LCDs).
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