| As an ultra-thin and one-atom-thick two dimensional nanomaterial, graphene has attracted intense interest amongst science researchers since its experimental discovery by mechanical exfoliation method in 2004. Due to its small atomic-sized thickness, the chemical, electrical, thermal, mechanical and optical properties of graphene are able to be tuned effectively using external techniques, such as doping, surface and lattice defect engineering, strain engineering and so on. Of these, strain engineering has received most attention. On the one hand, graphene is the strongest nanomaterial measured and small or larger strain (up to 30%) can be readily applied to graphene, which makes strain engineering possible. On the other hand, external strain can be applied to graphene repetitively with great accurate, which can tune graphene’s properties accurately.Recent years, graphene has found important applications in photoelectric detectors, sensors, photovoltaic devices and other fields. However, the optical absorption of single-layer graphene has a universal value of around πα(?)2.3% for visible light, depending on the fine structure constant α. Because of the weak light-graphene coupling, the graphene’s application would be limited.We have combined strain engineering and TIR (total internal reflection) realized larger tunable optical absorption of large-area CVD graphene under TIR by strain engineering, which has greatly improved the optical absorption of graphene. The main contents of this thesis are as follows:Firstly, summarize several important prepare and characterize methods of graphene. We also introduce graphene’s applications in photoelectric devices and the research meaning of this paper.Secondly, study on how the optical absorption of graphene is tuned by strain engineering under direct optical transmission. With a given sized external uniaxial strain applied to graphene, there will be a band-opening and red or blue shift of the 2D band and G band. Strain would tune the conductivity and transparency of graphene significantly by breaking the equivalence of sublattice of graphene. With the variation of incident angle, the optical absorption of graphene is periodic modulated by external strain.Thirdly, study on the optical absorption of graphene under TIR. The light transmission and reflection properties of multilayered structure were theoretically calculated. Then the optical absorption of graphene for TM wave and TE wave under TIR were simulated with Matlab programs.Fourthly, study on larger optical absorption of large-area CVD graphene under TIR by strain engineering. The results indicate that the optical absorption for both TM wave and TE wave can be separately tuned by controlling the direction of external strain applied to graphene. This method has greatly enhanced light-graphene coupling, the modulation efficiency of optical absorption in monolayer graphene under TIR was measured to increase to around three times that for normal incidence. The increment of graphene’s optical absorption is highly depending on the layers of graphene, the monolayer’s increment is bigger than that bilayer’s under the same external strain. |
