Plasmonic gap governs much of the electromagnetic response of metamaterials. Meanwhile, nano and subnanometric gap control achieved by exceptional advancement of nanotechnology has paved the way for quantum plasmonics. However, practical applications have been hindered by difficulties of active nano-control over a broad spectral range. We report on mechanically nano-controllable plasmonic metamaterials fabricated on flexible substrate with a broad spectral response from the visible to the terahertz waves. By closing and opening the metallic nanogap via macroscopic control, we observed both classical and quantum plasmonic responses. Using our devices functioning between the two extreme regimes of classical gaps and full-contact mode, we achieve unprecedented performances of light modulation in a broad spectral range.
Atomic layer deposition is an efficient method for coating a few nanometer-thick alumina over a wafer scale. This method combined with the standard photolithography process was presented to fabricate metallic nanometer gaps that optically act in terahertz regimes. However, the cross-sectional view of the gap shape of the metal–insulator–metal nanogap structure varies depending on the conditions from the stepwise procedure. In specific, selecting photoresist materials, adding ion milling and chemical etching processes, and varying metal thicknesses and substrates result in various optical gap widths and shapes. Since the cross-sectional gap shape affects the field enhancement of the funneled electromagnetic waves via the nanogap, the control of tailoring the gap shape is necessary. Thus, we present five different versions of fabricating quadrangle-ring-shaped nanometer gap arrays with varying different kinds of outcomes. We foresee the usage of the suggested category for specific applications.
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