Properties of Graphene

1  Optical properties of graphene

Graphene is known to be the thinnest and hardest nanomaterial in the world. It is almost transparent. The single-layer graphene absorbs 2.3% of visible light, that is, the transmittance is 97.7%. According to the principle of refraction and interference, graphene with different layers will show different colors and contrasts under an optical microscope. Experiments have shown that large-area graphene films also have excellent optical properties, and their optical properties vary with the thickness of graphene. Graphene film is a typical transparent conductive film, which can replace traditional thin film materials such as indium tin oxide (ITO) and fluorine-doped indium oxide (FTO). In addition, when the intensity of incident light exceeds a certain critical value, the absorption of graphene will be saturated. This nonlinear optical phenomenon is called saturated absorption. Using this property, graphene can be used for ultra-fast photonic and optical device such as fiber lasers.

 

2  Electrical properties of graphene

Each carbon atom of graphene is sp2 hybridized, and it contributes the remaining one p-orbital electron to form a π bond, and the π electron can move freely, giving the graphene excellent conductivity. Since the interaction between the atoms is very strong, even if the surrounding carbon atoms collide at normal temperature, the electrons in the graphene are less disturbed. When electrons are transported in graphene, scattering is less likely to occur, and the transmission efficiency is 1.5×10 5 cm 2 /(V·s), which is about 140 times that of electron mobility in silicon. Its conductivity is up to 106s/m, and its resistivity is only about 10-6Ω·cm, which is lower than that of copper or silver. So it is the material with the lowest resistivity in the world. Because of its extremely low resistivity, fast electron migration, graphene is expected to be used to develop thinner next-generation electronic components or transistors. Since graphene is essentially a transparent, good conductor, it is also suitable for producing transparent touch screens, light panels, and even solar cells. As a new type of nanomaterials with the most thin, the maximum intensity and most conductive conductivity, graphene is known as "black gold" and "king of new materials".

 

3  Mechanical properties of graphene

Graphene have the crystal structure with the highest strength and hardness in the material. Its tensile strength and modulus of elasticity are 125 GPa and 1.1 TPa, respectively. The strength limit of graphene is 42 N/m2. The ideal graphene has a strength of about 100 times that of ordinary steel, and a graphene layer of 1 m2 can withstand a weight of 4 kg. As a typical two-dimensional reinforcement material, graphene has potential application value in the field of composite materials. 

 

4  Thermal properties of graphene

Graphene is harder than diamond and it can maintain its original shape at high temperatures because the carbon atoms in the graphene are regularly ordered. When an external force is applied to the graphene, the internal carbon atoms do not move but only bent and deformed, they can resist external forces and ensure their stability. The theoretical specific surface area of graphene can reach 2630m2/g. A microsensor made of graphene can sense a single atom or molecule. When gas adheres or detaches from the graphene surface, the adsorbed molecule changes the local carrier concentration of the graphene, resulting in a stepwise change in the resistance. Based on this feature, graphene can be used to make gas sensors. Theoretical calculations show that graphene and lithium can form a porous composite structure and have a strong hydrogen storage capacity.

 

5  Magnetic properties of graphene

Graphene tends to have ferromagnetism after hydrogenation because it has a pair of electron pairs at the edges after hydrogenation, which makes graphene magnetic. The researchers also tested the magnetic properties of graphene by changing the temperature in the presence of a magnetic field. It is proved that when the magnetic field strength is 1T and the temperature T<90K, graphene will exhibit paramagnetic characteristics; and when the temperature T>90K, graphene will exhibit diamagnetic characteristics.

 

6  Chemical properties of graphene

The electronic properties of graphene have received extensive attention. However, the chemical properties of graphene have have received little attention. To date, the chemical properties of graphene that we know is graphene can adsorb surrounding atoms and molecules (eg : Nitrogen dioxide, ammonia, potassium), and this property is somewhat similar to the activated carbon. Nitrogen dioxide, ammonia, and potassium are often used as donors or acceptors to change the concentration of carbon atoms inside the graphene. Since graphene and graphite are both allotropes of carbon, so they often have some similar properties from the chemical point of view, Therefore, it is possible to find the regularity of graphene by conducting experiments on graphite. And it is believed that more chemical properties of graphene will be discovered in the future.

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