Enhanced visibility of graphene: Effect of one-dimensional photonic crystal

Abstract

We investigate theoretically the light reflectance of a graphene layer prepared on the top of onedimensional Si/SiO2 photonic crystal (1DPC). It is shown that the visibility of the graphene layers is enhanced greatly when 1DPC is added, and the visibility can be tuned by changing the incident angle and light wavelengths. This phenomenon is caused by the absorption of the graphene layer and the enhanced reflectance of the 1DPC.PACS numbers: 78.40. Ri, 42.70.Qs, 42.79.Fm Graphene consists of a two-dimensional honeycomb lattice of carbon atoms and has been attracting attention recently due to its remarkable electronic properties and its potential application in nanoelectronics 1 . Graphene exhibits high crystal quality, an exotic Dirac-type spectrum, and ballistic transport on a submicro scale. Graphene samples are usually fabricated by a micromechnical cleavage of graphite. It is difficult to distinguish the single graphene layer from many graphitic pieces, even utilizing the atomic force, scanning-tunneling, and electron microscopes. A recent experiment demonstrated that the graphene visibility depends on both the thickness of the SiO 2 layer and the light wavelength 2 . They found that specific thicknesses (300nm and 100nm) are most suitable for its visual detection for the normal light incidence and attribute this phenomenon to the opacity of the graphene layer. Although the relative difference of the reflectance [the contrast C in Ref. (2)] is enhanced significantly, the absolute difference of the light reflectance is still quite low because it is determined by the weak absorption of the graphene layer. In order to enhance the visibility of graphene, i.e., the absolute and relative difference of the light reflectance of the graphene layer, we propose to prepare the graphene layer on the top of Si/SiO 2 one-dimensional photonic crystal(1DPC). This 1DPC shows a high dielectric contrast at the Si/SiO 2 interface (∆n ≈ 2.3) producing a high reflectance at normal incidence, and can be fabricated by different techniques, e.g., the separation-byimplantedoxygen technique 3 , sputtering 4 combined with solidsource Si molecular beam epitaxy 5 , and plasma-enhanced chemical vapor deposition 6 .In this Letter, we investigate theoretically the light reflectance of a graphene layer prepared on the top of Si/SiO 2 1DPC, as shown schematically in Fig. 1(a). We consider an asymmetric 1DPC: A 0 (AB) l , where l is an integer denoting the l -th layer. All layers are nonmagnetic (µ = 1) and are characterized by their permittivities ε A (SiO 2 layer), ε B (Si layer), and their thicknesses satisfywhere λ is the wavelength required by the observation. The thickness of the top SiO 2 layer is d = λ/2 √ ε A . We find that the differ- ence between the reflectance of the graphene layers with 1DPC can be enhanced greatly, even one order of magnitude larger than that without 1DPC. Furthermore, the visibility of the graphene can be tuned by the incident angle.We consider a light shedding on the graphene layer prepared on the top of Si/Si...

Layer Identification of Colorful Black Phosphorus

“…The relationship between the observed colors and layer numbers of BP sheets is theoretically analyzed by first constructing a reflection model based on the Fresnel law which is often used in thin film reflection light calculation . This model consists of a dielectric film (300 nm SiO 2 ) on a silicon wafer and a BP sheet added on the dielectric film, as shown by Figure a.…”

Visibility study of graphene multilayer structures

“…The advantage of optical microscopy is that, in addition to optical contrast, Raman spectra are also helpful in determining the thickness of graphene sheets So far, several papers have been published on visibility of graphene on SiO 2 coated Si substrates with or without a resist. [5][6][7][8][9][10][11] From application point of view, however, it is also of interest to know if graphene can be "seen" on other types of substrates or layers, in particular, those that are widely used for existing or will be potentially used for future electronic, optoelectronic and spintronic devices. Based on this background, in this paper we report on the visibility study of SLG, BLG and FLG on a wide range of metal, semiconductor and oxide layers or substrates.…”

Gate-tunable nearly total absorption in graphene with resonant metal back reflector

“…Similar to graphene with a 1DPC, the graphene layer and the metal film act as the mirrors of the Fabry-Perot Cavity. The THz wave propagates back and forth between these two mirrors, which leads to photon localization and enhances the absorption of graphene [41,47].…”

“…The weak absorbance of graphene is due to the fact that most of the incident THz wave is reflected because of the large real and imaginary parts of the conductivity of graphene for a large Fermi energy |ε F | [49]. A resonant back reflector such as 1DPC or metal can reduce the reflection of graphene [47,50] and lead to relatively weak photon localization [41], which are the key points for achieving nearly total THz absorption in graphene.…”

“…To model the THz absorption of graphene in this structure, the transfer matrix method is used [41,46,47]. The electric field of the TE mode and the magnetic field of the TM mode of THz waves in the l th layer is given by E l (y, z) = (A l e ikz z + B l e −ikz z )e −ikyy e x and H l (y, z) = (A l e ikz z + B l e −ikzz )e −ikyy e x , respectively.…”