Infrared spectroscopy of graphene

Ju, Long; Horng, Jason; Chen, Chi-Fan; Geng, Baisong; Girit, Çaǧlar; Zhang, Yuanbo; Zhao, Hao; Bechtel, Hans A.; Martin, Michael; Zettl, A.; Wang, Feng

doi:10.1109/irmmw-thz.2011.6105038

Cited by 13 publications

(28 citation statements)

References 2 publications

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“…As noted earlier, the resonant frequency scales in proportion to n 1/4 w −1/2 , as for the case of uncontacted graphene ribbons considered in [3], indicating that ω 0 can be tuned through the application of a gate voltage or by adjusting the graphene width. The resonant frequency blue-shifts weakly with increasing the duty cycle w/Λ, but in all of the cases considered here the resonance frequency is lower than that of an uncontacted graphene ribbon of the same width.…”

Section: Introductionmentioning

confidence: 58%

“…In the contacted graphene, the metal regions act as capacitive reservoir for charge accumulation, and the graphene serves as an inductive channel, thus forming a resonant circuit that interacts strongly with the incident radiation. This is in striking contrast to the isolated ribbon case, where the coupling to incident radiation is weaker, and does not depend sensitively on the grating period [3,4,12]. The extension of the spatial mode also explains the significant reduction of plasmon frequency (predicted by the theory in Supplementary Section SS1 for the case Λ w) which is reduced by about a factor of √ 3 compared to that of an isolated graphene ribbon [11].…”

mentioning

confidence: 78%

“…However, when the metal contacts are made much wider than the graphene channel, a strong resonance emerges, characterized by high absorption in the graphene ribbon, at a resonant frequency that scales with n 1/4 w −1/2 , similar to the plasmon resonances in uncontacted graphene ribbons [3,12]. The surrounding material is assumed to be a uniform dielectric, in which case, the maximum achievable absorption in a thin-film (metal-graphene grating)…”

Section: Introductionmentioning

confidence: 99%

“…When these waves are confined to finite-sized graphene, plasmon resonances emerge that are characterized by alternating charge accumulation at the opposing edges of the graphene. The resonant frequency of such a structure depends on both the size and the surface charge density, and can be electrically tuned throughout the terahertz range by applying a gate voltage [3,4]. The promise of tunable graphene THz plasmonics has yet to be fulfilled, however, because most proposed optoelectronic devices including detectors, filters, and modulators [5][6][7][8][9][10] desire near total modulation of the absorption or transmission, and require electrical contacts to the graphene -constraints that are difficult to meet using existing plasmonic structures.…”

mentioning

confidence: 99%

“…The mobility and carrier density (electron or hole) were taken to be µ = 1000 cm 2 V −1 s −1 and n = 1.5 × 10 13 cm −2 , respectively. The array shows no discernable plasmon resonance when the period Λ and graphene width w are comparable, giving instead a Drude-like response.However, when the metal contacts are made much wider than the graphene channel, a strong resonance emerges, characterized by high absorption in the graphene ribbon, at a resonant frequency that scales with n 1/4 w −1/2 , similar to the plasmon resonances in uncontacted graphene ribbons [3,12]. The surrounding material is assumed to be a uniform dielectric, in which case, the maximum achievable absorption in a thin-film (metal-graphene grating)…”

mentioning

confidence: 99%

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Tunable Terahertz Hybrid Metal–Graphene Plasmons

et al. 2015

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Among its many outstanding properties, graphene supports terahertz surface plasma wavessub-wavelength charge density oscillations connected with electromagnetic fields that are tightly localized near the surface [1, 2]. When these waves are confined to finite-sized graphene, plasmon resonances emerge that are characterized by alternating charge accumulation at the opposing edges of the graphene. The resonant frequency of such a structure depends on both the size and the surface charge density, and can be electrically tuned throughout the terahertz range by applying a gate voltage [3,4]. The promise of tunable graphene THz plasmonics has yet to be fulfilled, however, because most proposed optoelectronic devices including detectors, filters, and modulators [5][6][7][8][9][10] desire near total modulation of the absorption or transmission, and require electrical contacts to the graphene -constraints that are difficult to meet using existing plasmonic structures. We report here a new class of plasmon resonance that occurs in a hybrid graphene-metal structure.The sub-wavelength metal contacts form a capacitive grid for accumulating charge, while the narrow interleaved graphene channels, to first order, serves as a tunable inductive medium, thereby forming a structure that is resonantly-matched to an incident terahertz wave. We experimentally demonstrate resonant absorption near the theoretical maximum in readily-available, large-area graphene, ideal for THz detectors and tunable absorbers. We further predict that the use of high mobility graphene will allow resonant THz transmission near 100%, realizing a tunable THz filter or modulator. The structure is strongly coupled to incident THz radiation, and solves a fundamental problem of how to incorporate a tunable plasmonic channel into a device with electrical contacts. In order to be applied in practical optoelectronic devices, graphene terahertz plasmonic resonators must be connected to an antenna, transmission line, metamaterial, or other electrical contact, in order to sense or apply a voltage or current, or to improve the coupling to free-space radiation. The conductive boundary screens the electric field and inhibits the accumulation of charge density at the opposing edges of the graphene channel, thus disrupting the traditional graphene plasmon mode. Until now, there was no experimental evidence that two-dimensional plasmons could be confined with conductive boundaries.In this letter, we demonstrate a new type of plasmon resonance in metal-contacted graphene, and we use analytic calculations, numerical simulations, and THz reflection and transmission measurements to confirm the principle of operation. These plasmon modes shows strong coupling to incident terahertz radiation, so that maximal absorption in graphene can be achieved at a resonance frequency that is gate-tunable. We also introduce an equivalent circuit model that predicts the resonant frequency, linewidth, and impedance matching condition of the fundamental plasmon mode, and can be used for d...

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Section: Introductionmentioning

confidence: 58%

mentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Tunable Terahertz Hybrid Metal–Graphene Plasmons

et al. 2015

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Actively tunable terahertz electromagnetically induced transparency analogue based on vanadium-oxide-assisted metamaterials

Zhang¹,

Yang²,

Han³

et al. 2020

Appl. Phys. A

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Recently, phase-change materials (PCMs) have drawn more attention due to the dynamically tunable optical properties. Here, we investigate the active control of electromagnetically induced transparency (EIT) analogue based on terahertz (THz) metamaterials integrated with vanadium oxide (VO2). Utilizing the insulator-to-metal transition of VO2, the amplitude of EIT peak can be actively modulated with a significant modulation depth. Meanwhile the group delay within the transparent window can also be dynamically tuned, achieving the active control of slow light effect. Furthermore, we also introduce independently tunable transparent peaks as well as group delay based on a double-peak EIT with good tuning performance. Finally, based on broadband EIT, the active tuning of quality factor of the EIT peak is also realized. This work introduces active EIT control with more degree of freedom by employing VO2, and can find potential applications in future wireless and ultrafast THz communication systems as multi-channel filters, switches, spacers, logic gates and modulators. Keywords: terahertz metamaterials; phase-change materials; vanadium oxide; electromagnetically induced transparency 1. Introduction Over the past decades, Metamaterials (MMs) have been focused continually due to the capability to manipulate electromagnetic (EM) waves in an unnatural way [1]. By designing artificial meta-resonators of MMs and arranging them appropriately, MMs can tailor lightwaves in subwavelength scale, consequently providing optical responses with desirable properties. In recent years, MMs have come to the terahertz (THz) regime [2]. Located between infrared and microwave band, THz radiations have enjoyed a rise of interest and are promising for security scanning [3], future wireless communications as well as the sixth-generation (6G) networks [3-5]. Now, MMshave been regarded as ideal platforms to achieve chipscale THz devices, such as THz sources [6,7], modulators [8,9], sensors [10,11] and absorbers [12,13].Recently, electromagnetically induced transparency (EIT) analogue in THz MMs have attracted more attention [14][15][16]. EIT refers to a sharp transparent window within a broad absorption spectrum, which comes from the quantum interference between two distinct excitation pathways in the natural three-level atom system [17]. Due to the dispersion properties, EIT has potential applications in slow light, optical data storage, nonlinear process enhancement and signal processing [18]. Mimicking EIT in the classical system, MMs can reproduce such effect via the near-field coupling between bright and dark modes supported on meta-resonators [14]. Compared with the conventional EIT, which requires severe experimental conditions [18], MM-based EIT analogue is easier to be produced and more stable, therefore suitable for practical chipscale applications [15].At the same time, for THz communication systems, THz devices with active tunability are required [19]. Therefore, various active optical materials have been utilized to turn passive MMs...

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Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

2017

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Vibrational sum frequency generation (VSFG) spectroscopy has been a powerful technique to probe molecular structures at non-centrosymmetric media. Recent developed heterodyne (HD) detection can further reveal spectral phase and molecular orientations. Adding imaging capability to an HD VSFG signal can bring spatial visualization capability into this non-linear optical technique. However, it has been a challenge to build an HD VSFG microscope that is both easy to align and has good spectral phase stability -two necessary criterions for the broad application of this technique into various areas of science. Here, we report a fully-collinear HD VSFG microscope, which meets both phase stability and optical alignment requirements that can spatially resolve images of molecular interfaces and domains, with chemical and structural sensitivities. The phase stability is more than nine times better than a Michelson Interferometric HD VSFG microscope. Using this HD VSFG microscope, we study the structures of molecular selfassembly films. Because of the superior phase sensitivity, we successfully identify two molecular domains with different molecular orientations, which we show is not possible to extract from an ensemble-averaged VSFG spectrum or homodyne-detected VSFG image.

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Infrared spectroscopy of graphene

Cited by 13 publications

References 2 publications

Tunable Terahertz Hybrid Metal–Graphene Plasmons

Tunable Terahertz Hybrid Metal–Graphene Plasmons

Actively tunable terahertz electromagnetically induced transparency analogue based on vanadium-oxide-assisted metamaterials

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

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