Plasma Carriers on Graphene: Relaxation of Plasma Carriers in Graphene: An Approach by Frequency‐Dependent Optical Conductivity Measurement (Advanced Optical Materials 14/2018)

Choi, Wookjin; Nishiyama, Hayate; Ogawa, Yui; Ueno, Yuko; Furukawa, Katsuko; Takeuchi, Tomohiro; Tsutsui, Yusuke; Sakurai, Tsuneaki; Seki, Shu

doi:10.1002/adom.201870054

Cited by 3 publications

(4 citation statements)

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“…In detail, a bias potential is applied between the ITO and a gold contact to electrically dope the graphene, which allowed us to controllably tune the electric potential over a sufficiently large range. Based on the plasma carrier model, the relaxation time of graphene can be determined from the voltage dependence of the complex permittivity ratio . Experimentally, with the field-induced time-resolved microwave conductivity technique, the real change in permittivity is estimated simultaneously with the dielectric loss, providing a detailed range of charge transport characteristics in the materials.…”

Section: Model and Methodsmentioning

confidence: 99%

“…Based on the plasma carrier model, the relaxation time of graphene can be determined from the voltage dependence of the complex permittivity ratio. 36 Experimentally, with the field-induced time-resolved microwave conductivity technique, 37 the real change in permittivity is estimated simultaneously with the dielectric loss, providing a detailed range of charge transport characteristics in the materials. If the patterned graphene structure is tuned through hole doping, which can be initiated by exposing the sample to the nitric acid vapor for several minutes, 38 the permittivity of graphene can be calculated through the equation ε = 1 + iσ(ω)/ε 0 tω where ε 0 is the permittivity of vacuum and t is the thickness of the monolayer graphene layer.…”

Section: Model and Methodsmentioning

confidence: 99%

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Active Control and Large Group Delay in Graphene-Based Terahertz Metamaterials

et al. 2019

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A distinct plasmon-induced transparency (PIT) window has been realized in our novel design of |+|-shaped graphene metamaterials, which consist of two identical graphene strips and a cross-shaped graphene resonator in the right middle. The two strips serve as the dark resonator, and the cross-shaped graphene plays the bright one. Active control of the PIT window can be modulated from the on state to the off state only by breaking structure symmetry. Furthermore, the PIT window can be dynamically adjusted with different Fermi energies in a noncontact way. More importantly, the proposed metamaterial structure achieves a maximum group delay of 13.28 ps, which is much higher than that in the previous paper. In the case of sensing application, the position of the PIT window has been investigated with different embedded media, and it shows a linear function of the refraction index. This study may open up new avenues for the development of highly integrated optical filters, optical sensors, or integrated optical switches.

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Section: Model and Methodsmentioning

confidence: 99%

Section: Model and Methodsmentioning

confidence: 99%

Active Control and Large Group Delay in Graphene-Based Terahertz Metamaterials

et al. 2019

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“…[47] When τ changes, σ in Equation ( 5) changes so that the impedance of the absorber also changes, resulting in a change in the absorbance of graphene. [48] Figure 5 shows the absorption characteristics of the graphenebased array structure at different relaxation times, τ. It is noticed that as τ increases from 0.8 ps to 3 ps, the frequencies of Mode I and Mode II do not change, the absorption bandwidths tend to decrease, and both absorption peaks respectively reach 0.995 and 0.999 at τ ¼ 1ps, but decrease when τ>1ps.…”

Section: Influence Of the Relaxation Time Of Graphene On The Absorbermentioning

confidence: 99%

“…[ 47 ] When τ changes, σ in Equation () changes so that the impedance of the absorber also changes, resulting in a change in the absorbance of graphene. [ 48 ]…”

Section: Dynamic Tuning Of the Absorbermentioning

confidence: 99%

Tunable Perfect Absorber of Graphene Metamaterial in the Terahertz Band and Its Sensing Properties

Zhu

Yin

2022

Advanced Photonics Research

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Herein, a dual‐band tunable ideal absorber based on graphene array, and the dynamic tuning performance of the perfect absorber in the terahertz band and its sensing properties based on graphene metamaterials are studied. The absorber shows two perfect absorption peaks at 1.01 and 1.86 THz, with an absorbance of 99.5% and 99.9%, respectively. With an elevation angle in the range of 0°–30° and a frequency in the range of 0.971–1.100 THz or 1.794–1.897 THz, the absorber designed herein can achieve an absorbance greater than 90%. Owing to the superior properties of graphene, dynamic tuning of the absorption frequency band, absorption bandwidth, and relative bandwidth of the absorber can be achieved by adjusting the Fermi level of graphene. In addition, adjusting the relaxation time realizes dynamic tuning of the absorption bandwidth and the absorbance with constant resonant frequency and fixed geometric parameters. Moreover, the sensitivity of the absorber reaches 492.5 GHz/RIU, which can achieve the sensing resolution required for the resonance frequency. This research provides a new concept for the development of high‐performance terahertz devices.

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Electron Transport over 2D Molecular Materials and Assemblies

Seki,

Paitandi,

Choi

et al. 2024

Acc. Chem. Res.

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Conspectus Two-dimensional (2D) molecular materials, in which the major interactions are confined in 2D planes with contrasted force fields acting in between the planes, have been key electronic functional materials since the past decade. Even without referring to the functionals of graphene-based systems, 2D electronic conjugated systems are expected to show extrawide dynamic ranges in electronic density of states (DOS) tuning, effective electron mass, electron mobility, and conductivity. A major advantage of 2D electronic systems is their compatibility with the ubiquitous electronic devices designed using planar structures, such as transistors and memories, which is associated with the utility of 2D active materials. The mobility of electrons in 2D systems is the key to their utility, and various conjugated molecular and 2D materials have been designed to optimize the mobility. This Account begins with an introduction for mobility assessment: using noncontact time-resolved microwave conductivity (TRMC) measurements as a technique to probe differential conductivity upon transient charge carrier injection into the materials. Electronic transport over 2D electronic materials such as graphenes, covalent organic frameworks (COFs), and metal–organic frameworks (MOFs) is discussed with a special emphasis on molecular building blocks, fine-tuning conducting species and linkages, topology of the framework, and controlling molecular doping. The superiority of β-ketoenamine-linked COF over imine-linked COF films in charge transport and dominant in-plane charge carrier mobility over out-of-plane mobility is also illustrated. Systematic molecular engineering of the building blocks of β-ketoenamine-linked COFs with varying degrees of donor–acceptor (D–A) conjugation, torsional angles, and reaction conditions resulted in the modulation of the efficiency of charge carrier generation/transport as well as exciton migration. The advantages of 2D systems are finally discussed in terms of the mobility interplaying with spatial arrangements of molecules as well as the substantial role of intermolecular interactions in stabilizing their condensed phases. The strong correlation between the dispersion of mobility and hierarchical intermolecular interactions sheds light on the way to overcome structural fluctuation on the optimization of charge transport in molecular electronic materials. The point of singularity in the dispersion at an intermolecular distance of d ∼ 0.3 nm is deduced from the overall mobility assessment in condensed phases of conjugated molecules, suggesting key roles of intermolecular electronic coupling: the new concept of electronic conjugation. Exceptional electronic coupling with relatively high charge carrier mobility was also observed, particularly in 2D spatial arrangements of chiral molecules in contrast to 3D analogues, where the reduction of gravitational density of the molecular condensates was impacting DOS: the Wallach’s rule. 2D electronic systems are strong candidates for the violation of the long-lasti...

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Plasma Carriers on Graphene: Relaxation of Plasma Carriers in Graphene: An Approach by Frequency‐Dependent Optical Conductivity Measurement (Advanced Optical Materials 14/2018)

Cited by 3 publications

References 0 publications

Active Control and Large Group Delay in Graphene-Based Terahertz Metamaterials

Active Control and Large Group Delay in Graphene-Based Terahertz Metamaterials

Tunable Perfect Absorber of Graphene Metamaterial in the Terahertz Band and Its Sensing Properties

Electron Transport over 2D Molecular Materials and Assemblies

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