scholarly journals Electrically Tunable Perfect Terahertz Absorber Using Embedded Combline Graphene Layer

2021 ◽  
Vol 11 (22) ◽  
pp. 10961
Author(s):  
Amir Maghoul ◽  
Ali Rostami ◽  
Azeez Abdullah Barzinjy ◽  
Peyman Mirtaheri
Keyword(s):  
Absorption Band ◽  
Graphene Layer ◽  
Absorption Peak ◽  
Absorption Intensity ◽  
Absorption Bandwidth ◽  
Graphene Layers ◽  
Terahertz Absorber ◽  
Terahertz Band ◽  
New Perspective ◽  
Insulator Substrate

Graphene is a powerful 2-D matter with the capability of extraordinary transparency, and tunable conductivity is employed in emerging optoelectronics devices. In this article, the design of an electrically tunable graphene-based perfect terahertz absorber is proposed and evaluated numerically. The introduced structure is composed of two graphene layers with a sharp absorption peak in the terahertz band. These graphene layers are combline and stripline separated by the insulator substrate. The position of the absorption peak is tunable on the absorption band by means of manipulation in geometric parameters of the combline graphene layer. Furthermore, the intensity and frequency of the absorption peak can be flexibly modulated by varying Fermi potential of the combline graphene layer, which can be controlled through external DC voltages without the need of changing the geometry of the structure. It is shown that the absorption band can be tuned in the bandwidth from 5 to 15 in terahertz. The findings of this paper can promote a new perspective in designing perfect ribbon absorbers based on graphene properties that can be utilized for future photodetectors, solar cells, and thermal sensors with an absorption intensity above 2 × 105(nm2) with narrow absorption bandwidth of 0.112 THz.

scholarly journals Coupling of waveguide mode and graphene plasmons

2021 ◽  
Vol 255 ◽  
pp. 07002
Author(s):  
Jiří Petráček ◽  
Jiří Čtyroký ◽  
Vladimír Kuzmiak ◽  
Pavel Kwiecien ◽  
Ivan Richter
Keyword(s):  
Low Power ◽  
Graphene Layer ◽  
Waveguide Mode ◽  
Chemical Potential ◽  
Temperature Sensing ◽  
Graphene Layers ◽  
Optical Wavelength ◽  
Electro Optic ◽  
Photonic Waveguides ◽  
Graphene Plasmons

Photonic waveguides with graphene layers have been recently studied for their potential as fast and low-power electro-optic modulators with small footprints. We show that in the optical wavelength range of 1.55 μm, surface plasmons supported by the graphene layer with the chemical potential exceeding ~0.5 eV can couple with the waveguide mode and affect its propagation. This effect might be possibly utilized in technical applications as a very low-power amplitude modulation, temperature sensing, etc.

scholarly journals Combined Mie Resonance Metasurface for Wideband Terahertz Absorber

2018 ◽  
Vol 8 (9) ◽  
pp. 1679
Author(s):  
Jie Hu ◽  
Tingting Lang ◽  
Changyu Shen ◽  
Liyang Shao
Keyword(s):  
Electric Fields ◽  
Incident Angle ◽  
Absorption Frequency ◽  
Variable Parameters ◽  
Absorption Bandwidth ◽  
Terahertz Absorber ◽  
Mie Resonance ◽  
Traditional Design ◽  
Single Block ◽  
Application Fields

In this paper, we propose a combined metasurface consisting of an aluminum substrate and an array of TiO2 blocks to achieve a wideband terahertz absorber. We incorporated several similar dielectric blocks with different side length into each unit cell. Each dielectric block could cause magnetic-resonance-inducing absorption effect with different peak wavelengths. Thus, our combined metasurface could achieve wider absorption frequency band than the traditional design when these dielectric blocks were properly designed. The absorption bandwidth could be widened nearly 2.5 times and 5 times compared to a single block case when there were four and nine blocks, respectively, andcouldbe further improved by increasing the number of combinations in structures (variable parameters included number, spacing, dimensions etc.). For both TE00 (the electric fields of the light polarized along the y-axis) and TM00 (the electric fields of the light polarized along the x-axis) polarization states, the absorption bandwidth could be widened effectively; even when the incident angle was 45°, the absorption rate could still reach about 75%. This structure is simple and easy to fabricate, and this design concept can also be used in various other application fields.

scholarly journals Quasicrystalline 30° twisted bilayer graphene as an incommensurate superlattice with strong interlayer coupling

2018 ◽  
Vol 115 (27) ◽  
pp. 6928-6933 ◽  
Author(s):  
Wei Yao ◽  
Eryin Wang ◽  
Changhua Bao ◽  
Yiou Zhang ◽  
Kenan Zhang ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Graphene Layer ◽  
Rotational Symmetry ◽  
Reciprocal Lattice ◽  
Double Resonance ◽  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Lattice Vector ◽  
Graphene Layers ◽  
Twisted Bilayer Graphene

The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moiré period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence. Here we report the successful growth of quasicrystalline 30° twisted bilayer graphene (30°-tBLG), which is stabilized by the Pt(111) substrate, and reveal its electronic structure. The 30°-tBLG is confirmed by low energy electron diffraction and the intervalley double-resonance Raman mode at 1383 cm−1. Moreover, the emergence of mirrored Dirac cones inside the Brillouin zone of each graphene layer and a gap opening at the zone boundary suggest that these two graphene layers are coupled via a generalized Umklapp scattering mechanism—that is, scattering of a Dirac cone in one graphene layer by the reciprocal lattice vector of the other graphene layer. Our work highlights the important role of interlayer coupling in incommensurate quasicrystalline superlattices, thereby extending band structure engineering to incommensurate superstructures.

scholarly journals Dual-Tunable Broadband Terahertz Absorber Based on a Hybrid Graphene-Dirac Semimetal Structure

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1096
Author(s):  
Jiali Wu ◽  
Xueguang Yuan ◽  
Yangan Zhang ◽  
Xin Yan ◽  
Xia Zhang
Keyword(s):  
Fermi Energy ◽  
Incident Angle ◽  
Normal Incidence ◽  
Surface Conductivity ◽  
Chemical Doping ◽  
Absorption Bandwidth ◽  
Terahertz Absorber ◽  
Dirac Semimetal ◽  
High Absorption ◽  
Broadband Terahertz

A dual-controlled tunable broadband terahertz absorber based on a hybrid graphene-Dirac semimetal structure is designed and studied. Owing to the flexible tunability of the surface conductivity of graphene and relative permittivity of Dirac semimetal, the absorption bandwidth can be tuned independently or jointly by shifting the Fermi energy through chemical doping or applying gate voltage. Under normal incidence, the device exhibits a high absorption larger than 90% over a broad range of 4.06–10.7 THz for both TE and TM polarizations. Moreover, the absorber is insensitive to incident angles, yielding a high absorption over 90% at a large incident angle of 60° and 70° for TE and TM modes, respectively. The structure shows great potential in miniaturized ultra-broadband terahertz absorbers and related applications.

scholarly journals The electronic thickness of graphene

2020 ◽  
Vol 6 (11) ◽  
pp. eaay8409 ◽  
Author(s):  
Peter Rickhaus ◽  
Ming-Hao Liu ◽  
Marcin Kurpas ◽  
Annika Kurzmann ◽  
Yongjin Lee ◽  
...  
Keyword(s):  
Graphene Layer ◽  
Finite Thickness ◽  
Tight Binding ◽  
Single Layer ◽  
Energy Difference ◽  
Quantum Capacitance ◽  
Density Range ◽  
Dielectric Thickness ◽  
Graphene Layers ◽  
Fabry Perot

When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K′ points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance Cm and is therefore suited to extract Cm. We explain the large observed value of Cm by considering the finite dielectric thickness dg of each graphene layer and determine dg ≈ 2.6 Å. In a second experiment, we map out the entire density range with a Fabry-Pérot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.

Deep UV Raman Spectroscopy of Epitaxial Graphenes on Vicinal 6H-SiC Substrates

2010 ◽  
Vol 645-648 ◽  
pp. 611-614
Author(s):  
Susumu Kamoi ◽  
Noriyuki Hasuike ◽  
Kenji Kisoda ◽  
Hiroshi Harima ◽  
Kouhei Morita ◽  
...  
Keyword(s):  
Graphene Layer ◽  
Peak Frequency ◽  
Epitaxial Graphene ◽  
Intensity Increase ◽  
Band Frequency ◽  
Graphene Layers ◽  
Exfoliated Graphene ◽  
Uv Raman Spectroscopy ◽  
Uv Raman ◽  
Deep Ultraviolet

We report microscopic Raman scattering studies of epitaxial graphene grown on SiC substrates using a deep-ultraviolet (UV) laser excitation at 266 nm to elucidate the interaction between the graphene layer and the substrate. The samples were grown on the Si-face of vicinal 6H-SiC (0001) substrates by sublimation of Si from SiC. The G band of the epitaxial graphene layer was clearly observed without any data manipulation. Increasing the number of graphene layers, the peak frequency of the G-band decreases linearly, while the peak width and the intensity increase. The G-band frequency of the graphene layers on SiC is higher than those of exfoliated graphene, which has been ascribed to compression from the substrate.

Graphene Layers on Silicon Carbide Studied by Raman Spectroscopy

2008 ◽  
Vol 600-603 ◽  
pp. 567-570 ◽  
Author(s):  
Jonas Röhrl ◽  
Martin Hundhausen ◽  
Konstantin V. Emtsev ◽  
Thomas Seyller ◽  
Lothar Ley
Keyword(s):  
Silicon Carbide ◽  
Raman Spectroscopy ◽  
Light Scattering ◽  
Graphene Layer ◽  
Monolayer Graphene ◽  
Spectroscopy Study ◽  
Graphene Layers ◽  
Layer Graphene ◽  
Micro Raman Spectroscopy ◽  
Few Layer Graphene

We present a micro-Raman spectroscopy study on single- and few layer graphene (FLG) grown on the silicon terminated surface of 6H-silicon carbide (SiC). On the basis of the 2D-line (light scattering from two phonons close to the K-point in the Brillouin zone) we distinguish graphene mono- from bilayers or few layer graphene. Monolayers have a 2D-line consisting of only one component, whereas more than one component is observed for thicker graphene layers. Compared to the graphite the monolayer graphene lines are shifted to higher frequencies. We tentatively ascribe the corresponding phonon hardening to strain in the first graphene layer.

Janus-like Fe3O4/PDA vesicles with broadening microwave absorption bandwidth

2018 ◽  
Vol 6 (29) ◽  
pp. 7790-7796 ◽  
Author(s):  
Xiaofeng Shi ◽  
Zhengwang Liu ◽  
Wenbin You ◽  
Xuebing Zhao ◽  
Renchao Che
Keyword(s):  
Microwave Absorption ◽  
Coupling Effect ◽  
Magnetic Coupling ◽  
Strong Absorption ◽  
Frequency Range ◽  
Absorption Intensity ◽  
Absorption Bandwidth ◽  
Measured Frequency ◽  
Measured Frequency Range ◽  
Pda Vesicles

Fe3O4/PDA vesicle Janus nanospheres were successfully synthesized, and they exhibited an ultra-wide effective band as wide as 11.6 GHz, covering 73% of the whole measured frequency range (2–18 GHz), and a strong absorption intensity as high as −50.0 dB due to the asymmetric polarization and magnetic coupling effect.

scholarly journals Raman Spectroscopy Imaging of Exceptional Electronic Properties in Epitaxial Graphene Grown on SiC

Nanomaterials ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 2234
Author(s):  
A. Ben Gouider Trabelsi ◽  
F. V. Kusmartsev ◽  
A. Kusmartseva ◽  
F. H. Alkallas ◽  
S. AlFaify ◽  
...  
Keyword(s):  
Graphene Layer ◽  
Longitudinal Optical ◽  
Epitaxial Graphene ◽  
Charge Carrier Concentration ◽  
Longitudinal Optical Phonon ◽  
Electrical Measurements ◽  
Graphene Layers ◽  
Fundamental Research ◽  
Application Fields ◽  
High Degree

Graphene distinctive electronic and optical properties have sparked intense interest throughout the scientific community bringing innovation and progress to many sectors of academia and industry. Graphene manufacturing has rapidly evolved since its discovery in 2004. The diverse growth methods of graphene have many comparative advantages in terms of size, shape, quality and cost. Specifically, epitaxial graphene is thermally grown on a silicon carbide (SiC) substrate. This type of graphene is unique due to its coexistence with the SiC underneath which makes the process of transferring graphene layers for devices manufacturing simple and robust. Raman analysis is a sensitive technique extensively used to explore nanocarbon material properties. Indeed, this method has been widely used in graphene studies in fundamental research and application fields. We review the principal Raman scattering processes in SiC substrate and demonstrate epitaxial graphene growth. We have identified the Raman bands signature of graphene for different layers number. The method could be readily adopted to characterize structural and exceptional electrical properties for various epitaxial graphene systems. Particularly, the variation of the charge carrier concentration in epitaxial graphene of different shapes and layers number have been precisely imaged. By comparing the intensity ratio of 2D line and G line—“I2D/IG”—the density of charge across the graphene layers could be monitored. The obtained results were compared to previous electrical measurements. The substrate longitudinal optical phonon coupling “LOOPC” modes have also been examined for several epitaxial graphene layers. The LOOPC of the SiC substrate shows a precise map of the density of charge in epitaxial graphene systems for different graphene layers number. Correlations between the density of charge and particular graphene layer shape such as bubbles have been determined. All experimental probes show a high degree of consistency and efficiency. Our combined studies have revealed novel capacitor effect in diverse epitaxial graphene system. The SiC substrate self-compensates the graphene layer charge without any external doping. We have observed a new density of charge at the graphene—substrate interface. The located capacitor effects at epitaxial graphene-substrate interfaces give rise to an unexpected mini gap in graphene band structure.

Low-Temperature Chemical Vapor Deposition Growth of Graphene Layers on Copper Substrate Using Camphor Precursor

2020 ◽  
Vol 20 (12) ◽  
pp. 7698-7704
Author(s):  
K. Kavitha ◽  
Akanksha R. Urade ◽  
Gurjinder Kaur ◽  
Indranil Lahiri
Keyword(s):  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Vapor Deposition ◽  
Graphene Layer ◽  
Copper Substrate ◽  
Chemical Vapor ◽  
Large Area ◽  
Chemical Vapor Deposition Growth ◽  
Graphene Layers ◽  
Grown Graphene

A two-step, low-temperature thermal chemical vapor deposition (CVD) process, which uses camphor for synthesizing continuous graphene layer on Cu substrate is reported. The growth process was performed at lower temperature (800 °C) using camphor as the source of carbon. A threezone CVD system was used for controlled heating of precursor, in order to obtain uniform graphene layer. As-grown samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The results show the presence of 4–5 layers of graphene. As-grown graphene transferred onto a glass substrate through a polymer-free wet-etching process, demonstrated transmittance ~91% in visible spectra. This process of synthesizing large area, 4–5 layer graphene at reduced temperature represents an energy-efficient method of producing graphene for possible applications in opto-electronic industry.

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