2021-10-25
Graphene is a
single layer (monolayer) of carbon atoms, tightly bound in a hexagonal
honeycomb lattice. It is an allotrope of carbon in the form of a plane of
sp2-bonded atoms with a molecular bond length of 0.142 nanometres. Layers
of graphene stacked on top of each other form graphite, with an
interplanar spacing of 0.335 nanometres. The separate layers of graphene in
graphite are held together by van der Waals forces, which can be overcome
during exfoliation of graphene from graphite.
Graphene is the
thinnest compound known to man at one atom thick, the lightest material known
(with 1 square meter weighing around
0.77 milligrams), the strongest compound discovered (between 100-300
times stronger than steel with a tensile strength of 130
GPa and a Young's modulus of 1 TPa - 150,000,000 psi), the best
conductor of heat at room temperature (at (4.84±0.44) × 10^3 to (5.30±0.48)
× 10^3 W·m−1·K−1) and also the best conductor of electricity known
(studies have shown electron mobility at values of more
than 200,000 cm2·V−1·s−1). Other
notable properties of graphene are its uniform
absorption of light across the visible and near-infrared parts of the spectrum (πα ≈
2.3%), and its potential suitability for use in spin
transport.
Bearing this in
mind, one might be surprised to know that carbon is the second most abundant
mass within the human body and the fourth most abundant element in the universe
(by mass), after hydrogen, helium and oxygen. This makes carbon the chemical
basis for all known life on earth, making graphene potentially an eco-friendly,
sustainable solution for
an almost limitless number of applications. Since the discovery (or more
accurately, the mechanical obtainment) of graphene, applications within
different scientific disciplines have exploded, with huge gains being made
particularly in high-frequency
electronics, bio, chemical and magnetic sensors, ultra-wide
bandwidth photodetectors, and energy
storage and generation.
GRAPHENE
PRODUCTION CHALLENGES
Initially, the
only method of making large-area graphene was a very expensive and complex
process (of chemical vapour deposition, CVD) that involved the use of toxic
chemicals to grow graphene as a monolayer by exposing Platinum, Nickel or
Titanium Carbide to ethylene or benzene at high temperatures. There were no
alternatives of using crystalline epitaxy on anything other than a metallic
substrate. These production issues made graphene initially unavailable for
developmental research and commercial uses. Also, using the CVD graphene in
electronics was hindered by the difficulty of removing the graphene layers from
the metallic substrate without damaging the graphene.
However, studies in 2012 found that by analysing graphene’s interfacial adhesive energy, it is possible to effectively separate graphene from the metallic board on which it is grown, whilst also being able to reuse the board for future applications theoretically an infinite number of times, therefore reducing the toxic waste previously created in this process. Furthermore, the quality of the graphene that was separated by using this method was sufficiently high to create molecular electronic devices.
Research in growing CVD graphene has since progressed by the leaps, rendering the quality of graphene a non-issue to technological adoption, which is now governed by the cost of the underlying metal substrate. Nevertheless, research is still being undertaken to consistently produce graphene on custom substrates with control over impurities such as ripples, doping levels and domain size, whilst also controlling the number and relative crystallographic orientation of the graphene layers.
APPLICATIONS
Driving graphene research towards industrial applications requires coordinated efforts, such as the billion-euro EU project Graphene Flagship. After the first phase that lasted several years, Flagship researchers produced a refined graphene applications roadmap, that pinpoints the most promising application areas: composites, energy, telecommunications, electronics, sensors and imaging, and biomedical technologies.
Being able to create supercapacitors out of graphene will possibly be the largest step in electronic engineering in a long time. While the development of electronic components has been progressing at a very high rate over the last 20 years, power storage solutions such as batteries and capacitors have been the primary limiting factor due to size, power capacity and efficiency (most types of batteries are very inefficient, and capacitors are even less so). For example lithium-ion batteries face a trade-off between energy density and power density.
In initial tests carried out, laser-scribed graphene (LSG) supercapacitors demonstrated power density comparable to that of high-power lithium-ion batteries that are in use today. Not only that, but also LSG supercapacitors are highly flexible, light, quick to charge, thin, and as previously mentioned comparably very inexpensive to produce.
