What is Graphene?

Graphene is a hexagonal lattice of carbon atoms that connect to form a single sheet in two dimensions. Each carbon atom is bonded to three other carbon atoms in the x and y planes but nothing in the z plane. Therefore, a graphene sheet is atomically thick as it has the height of just one carbon atom. The thickness of graphene has been measured at ~0.4 - 1.7 nm, which is 250,000 times thinner than printer paper. Theoretically, there is no limit to the size that graphene sheets can become. The largest sheets of graphene have lengths on the centimetre scale which is ten million times larger than its thickness.

Graphene materials are part of a family of carbon-based materials, including carbon nanotubes and fullerenes. They have different structural forms of carbon that share a similar atomic arrangement. Graphite is made up of layers of graphene. There are weak inter-layer interactions that hold graphite together. The interactions are weak enough to allow the layers to slide over each other. This makes it easy to access individual layers of graphene.

The existence of graphene has been well-known for a long time, with TEM images of multi-layer graphene structures being taken as early as the 1940's. However, research into this material only properly began in 2004, when a simple method for isolating single layers of graphene was discovered.

Early work on graphene showed that its properties vastly exceeded those of the bulk layered graphite from which it was taken. Properties such as the strength showed that a single layer of the material is over 200 times stronger than steel. The mobility of charge carriers like electrons are comparable to that of bulk metals such as copper. Graphene's thermal conductivity is extremely high, allowing heat to pass through it almost without any resistance. Graphene is remarkably transparent despite being a good absorber of light. It absorbs about 2.3% of visible light, a significant amount given that it is only one atom thick.

Graphene Flake SEM — SEM images of a single graphene flake

All of these unique properties mean that graphene could find use in a wide variety of applications including electrochemical capacitor devices, anti-corrosion coatings, composite materials, transparent conducting films, thermal pastes, as well as sensing and biosensing applications.

Graphene Properties and Applications

Properties	Graphene
Dimensionality	2D
Thickness	~ 1 nm, one atom thick
Surface Area	Extremely high specific surface area - ~2600 m²/g
Appearance	Transparent and colorless
Strength	Strongest material known to exist: Tensile strength = 130 GPa Elastic Modulus = 1.1 TPa
Bonding	Each carbon participates in three σ bonds (C-C) and a π bond (hybridized sp² bonding) Bond lengths = 0.142 nm
Conductivity	Exceptionally electrically and thermally conductive: Thermal Conductivity = 5 x 10³ W/mK Electron Conductivity = 106 S/m Resistance = 31 Ω/sq Electron mobility = (2 x 10⁵ cm²/V.s) Zero-gap semiconductor/semimetal
Stability	Chemically reactive edges and surface which can be functionalised with other elements

Ultrahigh Surface Area

The ultrahigh specific surface area (~2600 m²/g ) of graphene is a result of it being 2D and therefore majority exposed surface. This property is crucial for surface active applications such as:

Energy storage: Graphene has a greater charge accumulation in supercapacitors resulting in high energy and power densities. This is as a result of its high surface area which leads to more efficient ion transport in lithium ion batteries.

Sensors: The surface of graphene is highly sensitive to changes in environment producing a measurable response to gases, biomolecules and chemicals. Graphene can be modified with receptors to enable selectivity.

Water purification: Graphene effectively removes contaminants and pathogens at a molecular level.

Composite materials: The high surface area ensures better interaction with the matrix material, enhancing the mechanical, thermal, and electrical properties of the composite.

Solar cells: Graphene improves the efficiency of charge collection and transport, leading to more efficient photovoltaic devices.

Conductive inks and coatings: Graphene enhances the conductivity of inks and pastes used in printed electronics, flexible circuits, and transparent conductive films.

High Strength

Graphene is the strongest material known to exist. It is predicted to withstand 130 GPa of stress before breaking. This is referred to as its tensile strength value. 130 GPa is approximately 1.2 million times greater than atmospheric pressure. For comparison, diamond has a tensile strength of 2.8 GPa which can be as high as 80-90 GPa on the microscale.

Graphene’s elastic modulus (1.1 TPa) describes the ratio of applied stress to change in shape. This huge value means that graphene holds strong under immense stress.

Being both incredibly strong and stiff as well as lightweight makes graphene suitable for a wide range of applications including:

Flexible Electronics: Graphene is seen as a strong alternative for current electrodes substrates such as ITO which is brittle and chemically unstable. Graphene has been used in light-emitting diodes, solar cells and field-effect transistors. Graphene is also being used within wearable electronics such as sensors which can monitor human health.

Mechanical Reinforcement: Even very low loadings of graphene within a composite material such as polymers or concrete can provide significant reinforcement. Less than 1% (by weight) graphene additives sees significant improvements. This makes graphene composites attractive for replacing metals in applications such as construction, automotive and aerospace.

Graphene-reinforced materials are being used to manufacture high-performance sports equipment, such as tennis rackets, bicycle frames, and helmets, offering improved strength and reduced weight. This includes grip on trainers which are 50% more hard wearing and last more than 1,000 miles.

Biomedicine: Graphene based nanocomposites have been used for tissue engineering and regenerative medicine. Graphene imparts high strength to the engineering of bone, nerve, heart and muscle. It can promote stem cells to grow and develop into specific types of cells.

Conductivity

Graphene is exceptionally electrically and thermally conductive. Graphene has an electron conductivity of 106 S/m and thermal conductivity of 5 x 10³ W/mK . Electrons can flow very easily (electron mobility is 2 x 10⁵ cm²/V.s ) with very little resistance (31 Ω/sq ). This makes graphene suitable for a range of electronic and thermal applications, including:

Thermal Applications

Graphene can be incorporated into thermal interface materials (TIMs) to enhance heat transfer between components, leading to more efficient cooling in electronics. ). Graphene has been used in the cooling of photovoltaic solar panels in order to reduce deterioration caused by high temperatures.

The high thermal conductivity and compatibility with different materials means graphene can be applied to reduce the build-up of heat. This is particularly useful for high-power-batteries where temperature rises can negatively impact performance or lead to cell rupture and in the worst cases explosions. Graphene can be used to improve thermal conductivity within a battery without degrading heat storage ability.

Learn More

Graphene vs Graphite

Graphene is a single layer of carbon atoms arranged in a hexagonal pattern, like a sheet of paper. Graphite, on the other hand, is made up of many layers of graphene stacked on top of each other, like a stack of paper.

Introduction to 2D Materials

The foundation of technology is the understanding of material systems. Specific material properties are required depending on the application.

What is Graphene Oxide?

Graphene oxide (GO) is a two-dimensional material with oxygen-functionalized surfaces, derived from graphite.

Safely Reducing Graphene Oxide

The conversion of graphene oxide back to graphene is therefore of huge interest to both the scientific and industrial community.

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