Giant Field Enhancements in Ultrathin Nanoslots above 1 Terahertz

Kim, Dasom; Jeong, Jeeyoon; Choi, Geunchang; Bahk, Young‐Mi; Kang, Tae Sun; Lee, Dukhyung; Thusa, Bidhek

doi:10.1021/acsphotonics.8b00151

Cited by 23 publications

(16 citation statements)

References 35 publications

(54 reference statements)

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“…Metallic nano‐trenches, or nano‐slots, are a viable solution to solving this issue, as fine tuning of the gap width leads to a very large change in the optical properties of the sample due to gap plasmon modes within the gap. [ 21–23 ] Most importantly, in these structures the gap width and the operating wavelengths are completely decoupled, which means that changing the gap width by a few nanometers can significantly change the optical properties of the slits or slots operating at millimeter or longer wavelengths. This has been partially demonstrated in active slot antennas where gap widths modulated from 5 to 2 nm by thermal expansion of metallic films caused 30% modulation of transmitted terahertz waves.…”

Section: Introductionmentioning

confidence: 99%

A Transformative Metasurface Based on Zerogap Embedded Template

Das

Yun

Park

et al. 2021

Advanced Optical Materials

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The ideals of reconfigurable metasurfaces would be operation in a broad frequency range with a high extinction ratio and fatigue resistivity. In this paper, all the above is achieved in the microwave regime by transforming a bare metallic film into well‐controlled nanometer sized gaps in a fully reversible manner. It is shown that adjacent metallic patterns deposited at different times can form “zero‐nanometer gaps,” or “zerogaps,” while maintaining the optical and electrical connectivity. The zerogaps readily open and recover with gentle bending and relaxing of the flexible substrate, precisely along the rims of the pre‐patterns of centimeter lengths. In a prototypical pattern of densely packed slit arrays, these gaps when opened serve as antennas achieving transparency for polarizations perpendicular to the length of the gap and shut off all the incident lights when closed. In such transformation between a polarizer and a mirror, 75% of transmission is observed with polarization extinction ratio of 7500 coming back down to 5 orders of magnitude extinction repeatable over 10 000 times. This work has long‐standing implications to metamaterials and metasurfaces as well as the fundamental aspect of extending a picometer scale distance controllability toward the wafer scale.

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Section: Introductionmentioning

confidence: 99%

A Transformative Metasurface Based on Zerogap Embedded Template

Das

Yun

Park

et al. 2021

Advanced Optical Materials

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“…This indicates that the gap-filling dielectric has been removed successfully without any apparent damage to the nano-trenches, leading to a decrease in the permittivity inside the gap and a subsequent decrease in effective indices within the gap. Figure 4b shows the theoretical spectra calculated with the coupled mode method [31,32], which have been successfully implemented in simulating nanostructures in long-wavelength regimes [33][34][35]. We modeled collapsing of the gap as an increase in imaginary permittivity of the gap material, i.e., an increase in conductivity, due to formation of metallic bridges in the gap.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 4 b shows the theoretical spectra calculated with the coupled mode method [ 31 , 32 ], which have been successfully implemented in simulating nanostructures in long-wavelength regimes [ 33 , 34 , 35 ]. We modeled collapsing of the gap as an increase in imaginary permittivity of the gap material, i.e., an increase in conductivity, due to formation of metallic bridges in the gap.…”

Section: Resultsmentioning

confidence: 99%

Ultra-Narrow Metallic Nano-Trenches Realized by Wet Etching and Critical Point Drying

et al. 2021

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A metallic nano-trench is a unique optical structure capable of ultrasensitive detection of molecules, active modulation as well as potential electrochemical applications. Recently, wet-etching the dielectrics of metal–insulator–metal structures has emerged as a reliable method of creating optically active metallic nano-trenches with a gap width of 10 nm or less, opening a new venue for studying the dynamics of nanoconfined molecules. Yet, the high surface tension of water in the process of drying leaves the nano-trenches vulnerable to collapsing, limiting the achievable width to no less than 5 nm. In this work, we overcome the technical limit and realize metallic nano-trenches with widths as small as 1.5 nm. The critical point drying technique significantly alleviates the stress applied to the gap in the drying process, keeping the ultra-narrow gap from collapsing. Terahertz spectroscopy of the trenches clearly reveals the signature of successful wet etching of the dielectrics without apparent damage to the gap. We expect that our work will enable various optical and electrochemical studies at a few-molecules-thick level.

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“…Recently, the thickness of devices has become even thinner. In case of ten-nanometer-thick devices, our previous work 7 has demonstrated that performance, e.g., field enhancement, of nano-plasmonic devices, is increased by 6-fold, compared to a hundred-nanometer-thick devices. Hence, fabrication and comprehensive investigation of optical properties of ultra-thin gold film are promising as well as essential.…”

Section: Introductionmentioning

confidence: 99%

Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Lee

Kim

Jeong

et al. 2019

Sci Rep

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Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultra-thin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices.

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Giant Field Enhancements in Ultrathin Nanoslots above 1 Terahertz

Cited by 23 publications

References 35 publications

A Transformative Metasurface Based on Zerogap Embedded Template

A Transformative Metasurface Based on Zerogap Embedded Template

Ultra-Narrow Metallic Nano-Trenches Realized by Wet Etching and Critical Point Drying

Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

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