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.

One of the most straightforward methods to actively control optical functionalities of metamaterials is to apply mechanical strain deforming the geometries. These deformations, however, leave symmetries and topologies largely intact, limiting the multifunctional horizon. Here, we present topology manipulation of metamaterials fabricated on flexible substrates by mechanically closing/opening embedded nanotrenches of various geometries. When an inner bending is applied on the substrate, the nanotrench closes and the accompanying topological change results in abrupt switching of metamaterial functionalities such as resonance, chirality, and polarization selectivity. Closable nanotrenches can be embedded in metamaterials of broadband spectrum, ranging from visible to microwave. The 99.9% extinction performance is robust, enduring more than a thousand bending cycles. Our work provides a wafer-scale platform for active quantum plasmonics and photonic application of subnanometer phenomena.

The convergence of nano‐optics with an aqueous environment is promising for future chemical or biological applications. While the rapid development in nanofabrication has led to the realization of sub‐10 nm nanogaps of various structures, coupling water into high aspect ratio metallic nanogaps with a well‐defined area is not yet demonstrated. Here, arrays of 10 nm wide metallic trenches are reported filled with dielectric, air, liquid water, and various molecules in optical hotspots. Due to the high height‐to‐width aspect ratio of 20:1 and strong gap plasmon coupling in the 10 nm width, the trenches show distinct spectral changes at terahertz frequencies under changing gap materials, from which the full etching and water filling of the 10 nm gap can be unambiguously confirmed. A 75% transmitted amplitude decrease is observed through 200 nm deep trenches upon water filling, which converts to an effective 1100‐fold increase in the water absorption coefficient. The gap‐filling scheme can be applied to distinguish different liquids with 400 attoliters of volume or to detect rhodamine 6G molecules inside the gap with surface‐enhanced Raman scattering. Accordingly, the scheme can also be applied to a general class of polar organic molecules suitable for various biological or chemical applications.

Metallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width‐to‐length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled‐mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.

Vanadium dioxide (VO2) is one of the most promising materials for active metasurfaces due to the insulator‐metal transition, urging the development of an etching‐free patterning method and realization of multifunctionality in various spectral bands. Here, without etching, photolithography of vanadium metal followed by thermal oxidation achieve all‐VO2 slit array metasurfaces that can be exploited as a multifunctional terahertz (THz) transparent electrode. The metasurfaces retain approximately constant THz transparency over the phase transition while the electrical conductivity of the VO2 lines changes about a thousand times, and near‐infrared (NIR) diffraction is switched selectively. Numerical simulation shows that, during the phase transition, a decrease in THz transmission through the VO2 lines is compensated for by funneling through the slits, which is especially efficient with a deep subwavelength period. On the contrary, at the NIR range, the optical path difference between the slits and the VO2 lines is controlled according to the VO2 phase, enabling switching between constructive and destructive interferences for a specific diffraction order. It is expected that the demonstrated patterning method and multifunctional THz transparency will promote VO2‐based metasurfaces, finding multispectral applications such as THz/NIR hybrid communication.

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We demonstrate a chip-scaled reversible terahertz (THz) resonator in which bending the flexible substrate outward breaks a diabolo array into a bowtie array. The resonance frequency shifts from 0.5 THz to nearly twofold (∼1.1 THz) as the resonator bends outward. Tunable THz spectroscopy achieved by mechanical bending is explained by theoretical simulation. For the cases of flattening/bending/reflattening, we analyze electrical current−voltage characteristic and optical properties in THz transmission spectra. While the current−voltage curves subsequently exhibit metal-, capacitor-, and tunneling-like results, THz transmittance shows twofold resonant behavior. In this behavior, we further demonstrated molecular sensing two materials, α-lactose and caffeine, on a single resonator. Considering the volume of the gap region, the detection limit of the molecules within the gap region for the bowtie antenna array is 80.5 and 64.4 pg for lactose and caffeine, respectively. The detection limit is determined by terahertz transmission change (ΔT/T 0 ) and resonance frequency shift (Δf/f res ) caused by the molecules within the gap region due to terahertz field confinement. We expect that this approach provides a more stable and functional platform for THz sensing applications.

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