英语论文网

notubes is less than 1000 m2/g. The extra-large specific surface area is a superior advantagein many ways as the surface is where most physical and chemical reactions take place.Attributed to its tightly packed carbon atoms and a sp2 orbital hybridization, graphene exhibits excellent stability in harsh environments. More importantly, holes and vacancies in graphene sheets can be filled by simply exposing them to carbon-containing molecules, making graphene a material with self-repairing capability. Additionally, pure graphene shows great transparency (up to 95%), which is a necessity for applications in illumination (e.g., light emitting diode), energy harvesting (e.g., solar cell) and electronics (e.g., screens and interfaces).
 
Figure 2. (a) Honeycomb lattice of graphene; (b) Reciprocal lattice of the triangular lattice.
2.2 Electrical properties
Graphene exhibits excellent electrical conductivity(ballistic transport of electron carriers) with an intrinsic mobility of 200,000 cm2/V∙s in extreme cases and 15,000 cm2/V∙sunder ambient conditions, which are several orders of magnitude higher than that of copper, the most commonly used conductor nowadays. It is a zero-gap semiconductorwhose conduction and valence bands meet at the Dirac points (see Figure 3).The uniquehoneycomb lattice structure leads to the fact that the first Brillouinzone possesses two points on the edge that are non-equivalent to each other (K/K’points, which areknown as Dirac points). Thetight-bindingapproach focused on the nearest neighbour interactionprovides the dispersion relation of the electrons near the K/K’points:
           (1)
where α= √3 a_cc, acc is the length of C-C bond (0.142 nm), γ0 is the nearest-neighbor hopping energywith a magnitude of 2.8 eV. The positive sign applies to empty conduction (π) bands, while the negative sign corresponds to fully occupied valence (π*) bands.
The dispersion near the K/K’points can be obtained by:
           (2)
whereq ⃗is the momentum corresponding to the Dirac point, h ̅=h/2π and h is Planck’s constant. V_F=√3 ta/2 is the Fermi velocity and the value is 1×106 m/s.
Theelectrons’ linear dispersion relation can be described by:
        (3)
where k is a wave-vector measured from the Dirac points.
 
Figure 3. Electronic structure of graphene.
2.3 Mechanical properties
Previous studies claimed that graphene is the strongest natural material that has ever been discovered. The intrinsic tensile strength  and Young's modulus of defect free graphene are 130 GPa and 1 TPa, respectively(Lee et al., 2008), indicating outstanding mechanical strength. Meanwhile, the flexibility of graphene is (elastic modulus = 32 GPa)also reasonably high and can be further improved by introducing chemical cross-linking between individual layers. Additionally, the stiffness of graphene is 0.5 TPa and this material exhibits brittle fractures(as in cases of ceramic materials)(Zhang et al., 2014). Therefore, graphene may be used as pressure sensors.
2.4Magnetic properties
Previous
Potential applications
Current and future applications will be summarized to show the great potential of graphene in industrial applications.
Conclusions and perspectives本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。