Terahertz Nanoimaging of Graphene

Zhang, Jiawei; Chen, Xinzhong; Mills, Scott; Ciavatti, Thomas; Yao, Ziheng; Mescall, Ryan; Hu, Hai; Semenenko, Vyacheslav; Fei, Zhe; Li, Hua; Perebeinos, Vasili; Tao, Hu; Dai, Qing; Du, Xu; Liu, Mengkun

doi:10.1021/acsphotonics.8b00190

Cited by 89 publications

(94 citation statements)

References 45 publications

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“…3(c)) indeed results from pump induced carrier dynamics in InAs, which manifests itself as an increase of THz near-field reflectivity following optical excitation. Such photoinduced THz dynamics in InAs can be effectively screened by a single layer of graphene, which agrees with our previous observations: with high light momentum, graphene shows close to unity reflectivity at the THz frequencies despite the change of optical properties in the substrate [16].…”

Section: (C) and 4(d)) Upon Comparison Of The N-opte Dynamics Betweesupporting

confidence: 92%

“…In comparison, for THz near-field imaging, there is a strong contrast between the bare InAs substrate and the graphene, while the single layer and bilayer graphene are indistinguishable. We have previously reported on the similarity of THz near field signals among different layers of graphene and its close to unity signal level [16]. We note that for high quality graphene samples with typical doping at ambient environment conditions such as ours, it has been documented that the single layer and bilayer graphene are indistinguishable [26].…”

Section: Resultsmentioning

confidence: 52%

“…This specific sample is chosen to illustrate the unique near-field reflection and emission phenomena at THz frequencies in these two technologically important THz materials. Specifically, graphene has been demonstrated to possess unique far-infrared behavior in the extreme subwavelength regime [15,16]. Unlike in the mid-IR frequency range where plasmon propagation can be readily measured [17][18][19][20][21][22], the high momentum coupling between the photon and electrons in THz s-SNOM yields a strong tip-sample interaction and a close-to-perfect near-field THz reflection in high mobility graphene [16].…”

Section: Introductionmentioning

confidence: 99%

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Photo-induced terahertz near-field dynamics of graphene/InAs heterostructures

et al. 2019

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In this letter, we report optical pump terahertz (THz) near-field probe (n-OPTP) and optical pump THz near-field emission (n-OPTE) experiments of graphene/InAs heterostructures. Near-field imaging contrasts between graphene and InAs using these newly developed techniques as well as spectrally integrated THz nano-imaging (THz s-SNOM) are systematically studied. We demonstrate that in the near-field regime (/ 6000 λ), a single layer of graphene is transparent to near-IR (800 nm) optical excitation and completely "screens" the photo-induced far-infrared (THz) dynamics in its substrate (InAs). Our work reveals unique frequency-selective ultrafast dynamics probed at the near field. It also provides strong evidence that n-OPTE nanoscopy yields contrast that distinguishes single-layer graphene from its substrate.

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Section: (C) and 4(d)) Upon Comparison Of The N-opte Dynamics Betweesupporting

confidence: 92%

Section: Resultsmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

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Photo-induced terahertz near-field dynamics of graphene/InAs heterostructures

et al. 2019

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“…We clearly see the enormously enhanced signal-to-noise-ratio and material contrast for the lager tip radius, while the resolution seems to be diminished comparatively little. The contrast between graphene and the SiO2 substrate stems from the metallic conductivity of graphene 35 . More important, the comparatively weak contrast between h-BN and SiO2 can be recognized reliably only with the R = 500 nm tip.…”

Section: Description Of Setup Sample and Tipsmentioning

confidence: 99%

Probes for Ultrasensitive THz Nanoscopy

et al. 2019

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Scattering-type scanning near-field microscopy (s-SNOM) at terahertz (THz) frequencies could become a highly valuable tool for studying a variety of phenomena of both fundamental and applied interest, including mobile carrier excitations or phase transitions in 2D materials or exotic conductors. Applications, however, are strongly challenged by the limited signal-to-noise ratio. One major reason is that standard atomic force microscope (AFM) tips -which have made s-SNOM a highly practical and rapidly emerging tool -provide weak scattering efficiencies at THz frequencies. Here we report a combined experimental and theoretical study of commercial and custom-made AFM tips of different apex diameter and length, in order to understand signal formation in THz s-SNOM and to provide insights for tip optimization. Contrary to common beliefs, we find that AFM tips with large (micrometer-scale) apex diameter can enhance s-SNOM signals by more than one order of magnitude, while still offering a spatial resolution of about 100 nm at a wavelength of λ = 119 µm. On the other hand, exploiting the increase of s-SNOM signals with tip length, we succeeded in sub-15 nm (<λ/8000) resolved THz imaging employing a tungsten tip with 6 nm apex radius. We explain our findings and provide novel insights into s-SNOM via rigorous numerical modeling of the near-field scattering process. Our findings will be of critical importance for pushing THz nanoscopy to its ultimate limits regarding sensitivity and spatial resolution. TOC graphics

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“…Up to now, the near‐field study of polaritons continued to spur innovation and galvanize thought in a variety of photonics systems that extend to many different research fields . Later on, the graphene nanoimaging, and graphene plasmon nanoimaging, have become the touchstone of near‐field imaging systems, showing the capabilities of, for example, ultrafast s ‐SNOM, THz s ‐SNOM, and cryogenic s ‐SNOM …”

Section: Experimental Technique and Polariton Detectionmentioning

confidence: 99%

Nanoimaging and Nanospectroscopy of Polaritons with Time Resolved s‐SNOM

Yao

et al. 2019

Advanced Optical Materials

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The development of electronics and photonics is entering a new era of ultrahigh speed sensing, data processing, and telecommunication. The carrier frequencies of the next‐generation electronic devices inevitably extend beyond radio frequencies, marching toward the nominally photonics‐dominated territories, e.g., terahertz and beyond. As a result, electronic and photonic techniques naturally merge and seek common ground. At the forefront of this technical trend is the field of polaritonics, where polaritons are half‐light, half‐matter quasiparticles that carry the properties of both “bare” photons and “bare” dipole‐carrying excitations. The Janus‐faced nature of polaritons renders the unique capability of operando control using photoexcitation or applied electric field. Here, state‐of‐the‐art ultrafast polaritonic phenomena probed by scattering‐type scanning near‐field optical microscope (s‐SNOM) techniques is reviewed. The ultrafast dynamical control and loss‐reduction of the polariton propagation are discussed with special emphasis on the creation and probing of the tip or edge induced plasmon– and phonon–polaritons in low‐dimensional systems. The detailed technical aspects of s‐SNOM and its possible future development are also presented.

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Terahertz Nanoimaging of Graphene

Cited by 89 publications

References 45 publications

Photo-induced terahertz near-field dynamics of graphene/InAs heterostructures

Photo-induced terahertz near-field dynamics of graphene/InAs heterostructures

Probes for Ultrasensitive THz Nanoscopy

Nanoimaging and Nanospectroscopy of Polaritons with Time Resolved s‐SNOM

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