Plasmonic Ruler With Angstrom Distance Resolution Based on Double Metal Blocks

We propose a plasmonic ruler comprised of two silver blocks separated by a nanometer-level air gap. A plasmonic cavity mode with one intensity node could suppress radiative loss, providing a high quality factor of 52 and a narrow linewidth of 29 nm, at a resonant wavelength of 1533 nm and a gap thickness of 2 nm. In simulation, a change of only 0.1 nm in the gap thickness of 2 nm results in a large wavelength shift of 40 nm in the resonance spectrum, which is larger than the linewidth, so that the shift is clearly observable. The proposed plasmonic ruler with Angstrom distance resolution, which alleviates the complexity of the metallic structures using only two blocks and achieves high sensitivity and sharp linewidth, would be useful to monitor a minute change in distances during molecular processes.