The world’s thinnest and strongest material with remarkable
electrical, thermal and optical properties at your finger tips
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Graphene Supplier to Industry, Australia
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Frequently Asked Questions
What are the properties of Graphene?
Before monolayer graphene was isolated in 2004, it was theoretically believed that two dimensional
compounds could not exist due to thermal instability when separated. However, once graphene was isolated,
it was clear that it was actually possible, and it took scientists some time to find out exactly how. After
suspended graphene sheets were studied by transmission electron microscopy, scientists believed that they
found the reason to be due to slight rippling in the graphene, modifying the structure of the material.
However, later research suggests that it is actually due to the fact that the carbon to carbon bonds in
graphene are so small and strong that they prevent thermal fluctuations from destabilizing it.
One of the most useful properties of graphene is that it is a zero-overlap semimetal (with both holes and electrons as charge carriers) with very high
electrical conductivity. Carbon atoms have a total of 6 electrons; 2 in the inner shell and 4 in the outer shell. The 4 outer shell electrons in an individual
carbon atom are available for chemical bonding, but in graphene, each atom is connected to 3 other carbon atoms on the two dimensional plane, leaving 1
electron freely available in the third dimension for electronic conduction. These highly-mobile electrons are called pi (π) electrons and are located above and
below the graphene sheet. These pi orbitals overlap and help to enhance the carbon to carbon bonds in graphene. Fundamentally, the electronic properties
of graphene are dictated by the bonding and anti-bonding (the valance and conduction bands) of these pi orbitals.
Combined research over the last 50 years has proved that at the Dirac point in graphene, electrons and holes have zero effective mass. This occurs
because the energy – movement relation (the spectrum for excitations) is linear for low energies near the 6 individual corners of the Brillouin zone. These
electrons and holes are known as Dirac fermions, or Graphinos, and the 6 corners of the Brillouin zone are known as the Dirac points. Due to the zero
density of states at the Dirac points, electronic conductivity is actually quite low. However, the Fermi level can be changed by doping (with electrons or
holes) to create a material that is potentially better at conducting electricity than, for example, copper at room temperature.
Tests have shown that the electronic mobility of graphene is very high, with previously reported results above 15,000 cm2·V−1·s−1 and theoretically
potential limits of 200,000 cm2·V−1·s−1 (limited by the scattering of graphene’s acoustic photons). It is said that graphene electrons act very much like
photons in their mobility due to their lack of mass. These charge carriers are able to travel sub-micrometer distances without scattering; a phenomenon
known as ballistic transport. However, the quality of the graphene and the substrate that is used will be the limiting factors. With silicon dioxide as the
substrate, for example, mobility is potentially limited to 40,000 cm2·V−1·s−1.
Another of graphene’s stand-out properties is its inherent strength. Due to the strength of its 0.142 Nm-long carbon bonds, graphene is the strongest
material ever discovered, with an ultimate tensile strength of 130,000,000,000 Pascals (or 130 gigapascals), compared to 400,000,000 for A36 structural
steel, or 375,700,000 for Aramid (Kevlar). Not only is graphene extraordinarily strong, it is also very light at 0.77milligrams per square metre (for comparison
purposes, 1 square metre of paper is roughly 1000 times heavier). It is often said that a single sheet of graphene (being only 1 atom thick), sufficient in size
enough to cover a whole football field, would weigh under 1 single gram.
What makes this particularly special is that graphene also contains elastic properties, being able to retain its initial size after strain. In 2007, Atomic force
microscopic (AFM) tests were carried out on graphene sheets that were suspended over silicone dioxide cavities. These tests showed that graphene sheets
(with thicknesses of between 2 and 8 Nm) had spring constants in the region of 1-5 N/m and a Young’s modulus (different to that of three-dimensional
graphite) of 0.5 TPa. Again, these superlative figures are based on theoretical prospects using graphene that is unflawed containing no imperfections
whatsoever and currently very expensive and difficult to artificially reproduce, though production techniques are steadily improving, ultimately reducing costs
Graphene’s ability to absorb a rather large 2.3% of white light is also a unique and interesting property, especially considering that it is only 1 atom thick.
This is due to its aforementioned electronic properties; the electrons acting like massless charge carriers with very high mobility. A few years ago, it was
proved that the amount of white light absorbed is based on the Fine Structure Constant, rather than being dictated by material specifics. Adding another
layer of graphene increases the amount of white light absorbed by approximately the same value (2.3%). Graphene’s opacity of πα ≈ 2.3% equates to a
universal dynamic conductivity value of G=e2/4 (±2-3%) over the visible frequency range.
Due to these impressive characteristics, it has been observed that once optical intensity reaches a certain threshold (known as the saturation fluence)
saturable absorption takes place (very high intensity light causes a reduction in absorption). This is an important characteristic with regards to the mode-
locking of fibre lasers. Due to graphene’s properties of wavelength-insensitive ultrafast saturable absorption, full-band mode locking has been achieved
using an erbium-doped dissipative soliton fibre laser capable of obtaining wavelength tuning as large as 30 nm.
In terms of how far along we are to understanding the true properties of graphene, this is just the tip of the iceberg. Before graphene is heavily integrated
into the areas in which we believe it will excel at, we need to spend a lot more time understanding just what makes it such an amazing material.
Unfortunately, while we have a lot of imagination in coming up with new ideas for potential applications and uses for graphene, it takes time to fully
appreciate how and what graphene really is in order to develop these ideas into reality. This is not necessarily a bad thing, however, as it gives us
opportunities to stumble over other previously under-researched or overlooked super-materials, such as the family of 2D crystalline structures that graphene