Abstract

In this tutorial, we survey various methods to fabricate (sub)nanogaps, including how to change the gap width in-situ from zero to tens of nanometers. We define 'zerogap' in relation to the broad optical frequency, from microwaves to the visible and discuss potential applications. Flagship nanotechnologies such as the scanning tunneling microscopy (STM) and the atomic force microscopy heavily rely on their ability to control and maintain the gap width between the probe and the probed surface, often with picometer precisions. However matured these technologies are, their applications are limited to imaging or to single molecular manipulations because of the small device footprints of the zero-dimensional, ~1 nm² variable gap architectures. For photonic applications encompassing the microwave and terahertz regime, we need to vastly increase the effective length of the gap control to at leaset several wavelengths, to the truly macroscopic scale. We explore this very issue of how to extend the picometer distance controllability to the wafer-length; wafer-scale. Based on the atomic layer lithography, high aspect ratio-nanotrenches of 10 nm width, up to 2 cm-long are fabricated by etching-out the alumina spacer, on a flexible substrate¹. While our as-fabricated structure can be transparent to electromagnetic waves owing to the slot antenna action of the nanotrenches, inherently embedded point-contacts become activated when gentle bending closes the gap. Quantum plasmonic actions over the uniform length of nanotrenches traversing tunneling, quantized conductance and semi-classical regimes produce an extinction better than 10,000 repeatable over 10,000 times in real time that can alter resonance and symmetry as well. Our quantum line-contacts offer a versatile platform for macroscopic realization of microscopic phenomena.

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