The Optical Characteristics Of Photonic Crystals Containing Graphene Films

From 2004,after graphene films have been prepared by micromechanical cleavage experimentally,it has aroused great attention in the area of physics and material science.Graphene has only atomic layer thickness,and it has higher carrier mobility,better flexibility and stability than traditional semiconductor materials with the same thickness.As a unique optical property,the absorptance of the graphene is nearly invariable in the visible range.Therefore the applications of graphene to transparent electrodes,photoelectric detectors and photoelectric equipments are of great significance.However,the low absorptance of graphene limits its applications in optoelectronic devices that need strong light-graphene interactions,such as graphene-based photodetectors and optical absorbers.Therefore,many methods have been proposed to enhance the absorption of graphene.Since 1987,the concept of photonic crystals(PCs)was proposed,which have received widespread attention in the field of basic science.Its lattice dimension can be compared with the wavelength of the electromagnetic wave,and its basic feature is controlling the propagation of electromagnetic waves.Perfect PCs have the photonic band gap so the propagation of the electromagnetic wave can be banned in the specific wavelength range.If we insert defect layers in the PCs,defect modes will appear in the photonic band gap.The maximum transmittance of the electromagnetic wave at the wavelength of the defect mode is the unit.Therefore,it has the great significance by using PCs to enhance the interaction of the graphene and the light.In this paper,we prepared one-dimensional PCs and graphene films by electron beam evaporation method and wet transfer method experimentally,respectively.In theory,we use the transfer matrix method to simulate their optical properties.We mainly studied the enhanced and complete absorption using one-dimensional dielectric PCs containing graphene films in the visible range.In the second chapter,we mainly investigated the optical properties of heterostructure composed of graphene and one-dimensional PCs.Since the PCs can be as a dielectric mirror,the incident light is reflected completely in the forbidden band.After we put the graphene films on the surface of PCs,the absorption of graphene films is greatly enhanced in the photonic band gap.We theoretically and experimentally demonstrated that the absorption of graphene on the surface of the PCs is enhanced by?4 times for the spectral range within the forbidden gap of PCs over a wide range of incidence angle for both transverse electric(TE)and transverse magnetic(TM)polarizations compared with that of the free-standing graphene.In the third chapter,we mainly studied the optical properties of one-dimensional PCs containing defects and graphene films where the latter was inserted within the former.After we insert defect layers into PCs,there will be a defect mode in the photonic band gap.When the defect layer is lower-refractive-index medium,electric field intensity will strongly localize in the defect layer;when the defect layer is higher-refractive-index medium,electric field intensity is almost zero in the defect.Therefore,if we inserted graphene films in lower-refractive-index defect layer,its light absorption can be enhanced greatly.However,if we inserted graphene films in higher-refractive-index defect layer,the absorption of graphene reduced to zero.Here,we considered both symmetric and asymmetric defective PCs with graphene.In the fourth chapter,we theoretically investigated the optical absorption properties of graphene monolayer on the top of the truncated dielectric photonic crystals deposited on a prism in the visible range.Perfect absorption are realized since the Bloch surface modes are excited on the surface of the graphene monolayer.We found that the electromagnetic field intensity is strong localized in the graphene layers when we put graphene films on the top of the truncated dielectric photonic crystals.Furthermore,it is found that total absorption can be achieved at special oblique incident angles for both transverse electric and transverse magnetic polarizations.These absorption properties are important for designing graphene-based perfect optical absorbers.