Tunnelling current-voltage characteristics of Angstrom gaps measured with terahertz time-domain spectroscopy

Kim, Joonyeon; Kang, Bong Joo; Bahk, Young‐Mi; Kim, Yong Seung; Park, Joo Hyun; Kim, Dong-Won; Rhie, Jiyeah; Han, Sang-Hoon; Jeon, Hyeongtag; Park, Cheol-Hwan; Rotermund, Fabıan; Kim, Dai‐Sik

doi:10.1038/srep29103

Cited by 18 publications

(14 citation statements)

References 25 publications

(37 reference statements)

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“…4(c) which shows a plot of Δf as a function of the surface density and gap width; the frequency shift is larger and more rapidly saturated as the gap width decreases. This result can be understood by the enhancement of the electric field in the gap region as the gap width decreases [11,[28][29][30].…”

Section: Resultsmentioning

confidence: 94%

Sensing viruses using terahertz nano-gap metamaterials

Park

Shin

et al. 2017

Biomed. Opt. Express

151

117

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We demonstrate highly sensitive detection of viruses using terahertz split-ring resonators with various capacitive gap widths. Two types of viruses, with sizes ranging from 60 nm (PRD1) to 30 nm (MS2), were detected at low densities on the metamaterial surface. The dielectric constants of the virus layers in the THz frequency range were first measured using thick films, and the large values found identified them as efficient target substances for dielectric sensing. We observed the resonance-frequency shift of the THz metamaterial following deposition of the viruses on the surface at low-density. The resonance shift was higher for the MS2 virus, which has a relatively large dielectric constant. The frequency shift increases with surface density until saturation and the sensitivity is then obtained from the initial slope. Significantly, the sensitivity increases by about 13 times as the gap width in the metamaterials is decreased from 3 µm to 200 nm. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization.

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Section: Resultsmentioning

confidence: 94%

Sensing viruses using terahertz nano-gap metamaterials

Park

Shin

et al. 2017

Biomed. Opt. Express

151

117

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“…The generated free carrier density absorbs THz waves, expressing itself as an effective imaginary permittivity of the gap material, aluminum oxide [20,21,33]. The consequent decrease in transmission can, therefore, function as a direct probe for the local field enhancement at the metallic nanogaps [22]. In order to obtain high-field THz waves, we additionally use a regenerative amplifier and a lithium niobate crystal [34].…”

Section: Resultsmentioning

confidence: 99%

“…Among them negative slot or slit antenna structures possess the advantage of backgroundfree exclusive electromagnetic funneling when operated in transmission geometry, and is, therefore, capable of experimentally determining the near-field enhancement at the gap [19]. Such properties are advantageous in applications where quantitative analyses are highly required, such as in nonlinear experiments [10,[20][21][22] or when realizing molecular absorption or scattering enhancement [23][24][25]. Physical origins of the observed phenomena are mostly interpreted in terms of changes in transmission spectra, while the reflection counterpart, an excellent additional source of information, is usually not considered in the transmission type nanogaps.…”

Section: Introductionmentioning

confidence: 99%

Anomalous extinction in index-matched terahertz nanogaps

et al. 2017

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Slot-type nanogaps have been widely utilized in transmission geometry because of their advantages of exclusive light funneling and exact quantification of near-field enhancement at the gap. For further application of the nanogaps in electromagnetic interactions with various target materials, complementary studies on both transmission and reflection properties of the nanogaps are necessary. Here, we observe an anomalous extinction of terahertz waves interacting with rectangular ring-shaped sub-30 nm wide gaps. Substrate works as an index matching layer for the nanogaps, leading to a stronger field enhancement and increased nonlinearity at the gap under substrate-side illumination. This effect is expressed in reflection as a larger dip at the resonance, caused by destructive interference of the diffracted field from the gap with the reflected beam from the metal. The resulting extinction at the resonance is larger than 60% of the incident power, even without any absorbing material in the whole nanogap structure. The extinction even decreases in the presence of an absorbing medium on top of the nanogaps, suggesting that transmission and reflection from nanogaps might not necessarily represent the absorption of the whole structure.

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“…The nanogap structure in configuration of a metallic slit, composed of optically thick metal films extended far for many wavelengths in lateral direction and optically transparent insulating layer sandwiched between the metals, can be modeled by an equivalent circuit with appropriate parameters [96,97] as shown in Figure 11A. Here, the fields of the incident and transmitted light coincide with the applied current and voltage that are studied in impedance measurements.…”

Section: Terahertz Tunneling Transportmentioning

confidence: 99%

“…The shapes of the incident terahertz pulse time traces are shown as gray curves. The figures are reproduced from Reference [96].…”

Section: Terahertz Tunneling Transportmentioning

confidence: 99%

Terahertz quantum plasmonics at nanoscales and angstrom scales

2020

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Through the manipulation of metallic structures, light–matter interaction can enter into the realm of quantum mechanics. For example, intense terahertz pulses illuminating a metallic nanotip can promote terahertz field–driven electron tunneling to generate enormous electron emission currents in a subpicosecond time scale. By decreasing the dimension of the metallic structures down to the nanoscale and angstrom scale, one can obtain a strong field enhancement of the incoming terahertz field to achieve atomic field strength of the order of V/nm, driving electrons in the metal into tunneling regime by overcoming the potential barrier. Therefore, designing and optimizing the metal structure for high field enhancement are an essential step for studying the quantum phenomena with terahertz light. In this review, we present several types of metallic structures that can enhance the coupling of incoming terahertz pulses with the metals, leading to a strong modification of the potential barriers by the terahertz electric fields. Extreme nonlinear responses are expected, providing opportunities for the terahertz light for the strong light–matter interaction. Starting from a brief review about the terahertz field enhancement on the metallic structures, a few examples including metallic tips, dipole antenna, and metal nanogaps are introduced for boosting the quantum phenomena. The emerging techniques to control the electron tunneling driven by the terahertz pulse have a direct impact on the ultrafast science and on the realization of next-generation quantum devices.

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Tunnelling current-voltage characteristics of Angstrom gaps measured with terahertz time-domain spectroscopy

Cited by 18 publications

References 25 publications

Sensing viruses using terahertz nano-gap metamaterials

Sensing viruses using terahertz nano-gap metamaterials

Anomalous extinction in index-matched terahertz nanogaps

Terahertz quantum plasmonics at nanoscales and angstrom scales

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