Physical property.

• Internal structure.

       The arrangement of carbon atoms in graphene is the same as that in the single atom layer of graphite, and it has the following characteristics: carbon atoms have four valence electrons, three of which generate SP2 bond, that is, each carbon atom contributes an unbound electron in the PZ orbit, the PZ orbit of the nearest atom forms π bond perpendicular to the plane, and the newly formed π bond is half filled. The results show that the coordination number of carbon atom in graphene is 3, the bond length between two adjacent carbon atoms is 1.42 × 10-10 meters, and the angle between bond and bond is 120 °. In addition to the honeycomb layered structure in which the σ bond is linked with other carbon atoms to form a hexagon ring, the PZ orbit perpendicular to the layer plane of each carbon atom can form a large π bond (similar to benzene ring) of polyatoms throughout the whole layer, so it has excellent electrical and optical properties.

Figure 3. Graphene structure diagram

• Mechanical properties

       Graphene is one of the materials with the highest strength known, but also has good toughness and can be bent. The theoretical Young's modulus of graphene is 1.0tpa, and the inherent tensile strength is 130gpa. The reduced graphene modified by hydrogen plasma also has very good strength, and the average modulus is 0.25 TPA. The graphite paper made up of graphene flakes has many holes, so the paper is very brittle. However, after oxidation, the functional fossil graphene is obtained, and then the paper made of functional fossil graphene is very strong and tough.

Figure 4. Schematic diagram of graphene forming fullerene, carbon nanotubes and graphite

• Electronic effect

       The carrier mobility of graphene at room temperature is about 150000cm2 / (V · s), which is 10 times higher than that of silicon material, and more than twice that of InSb, the material with the highest carrier mobility. Under some special conditions, such as low temperature, the mobility of graphene can be as high as 250000 cm2 / (V · s). Unlike many materials, the electronic mobility of graphene is less affected by the temperature change. At any temperature between 50 and 500K, the electronic mobility of graphene monolayer is about 150000cm2 / (V · s).
In addition, the semi integer quantum Hall effect of the electron carrier and hole carrier in graphene can be observed by changing the chemical potential through the action of electric field, while scientists have observed the quantum Hall effect of graphene at room temperature. [8] The carrier in graphene follows a special quantum tunneling effect, and does not produce backscattering when it encounters impurities, which is the reason for the local super conductivity and high carrier mobility of graphene. There is no static mass of electrons and photons in graphene, and their velocity is a constant independent of kinetic energy.
Graphene is a zero distance semiconductor because its conduction and valence band meet at the Dirac point. At the six positions of Dirac point, the edge Brillouin of momentum space is divided into two groups of equivalent triplicate. In contrast, the main point of traditional semiconductor is usually γ, and the momentum is zero.

• Thermal properties

       Graphene has very good thermal conductivity. The thermal conductivity of pure and defect free graphene monolayer is as high as 5300w / MK, which is higher than that of single-walled carbon nanotubes (3500W / MK) and multi walled carbon nanotubes (3000W / MK). When it is used as a carrier, the thermal conductivity can also reach 600W / MK. In addition, the ballistic thermal conductivity of graphene can make the lower limit of the ballistic thermal conductivity of carbon nanotubes per unit circumference and length move down.