Mono-crystalline Gold Platelets: A High Quality Platform for Surface Plasmon Polaritons

TL;DR

This study demonstrates that mono-crystalline gold platelets serve as an excellent platform for surface plasmon polaritons, enabling detailed interference pattern analysis and long-distance SPP propagation with high quality.

Contribution

The paper introduces the use of mono-crystalline gold platelets for high-resolution SPP studies, showing their superior plasmonic properties and long-range SPP propagation capabilities.

Findings

SPP wavelength of 606 nm matches theoretical predictions

Clear interference patterns observed at 633 nm excitation

SPPs propagate over 20 micrometers with minimal loss

Abstract

We use mono-crystalline gold platelets with ultra-smooth surfaces and superior plasmonic properties to investigate the formation of interference patterns caused by surface plasmon polaritons (SPPs) with scattering-type scanning near-field microscopy (s-SNOM) at 521~nm and 633~nm. By applying a Fourier analysis approach, we can identify and separate several signal channels related to SPPs launched and scattered by the AFM tip and the edges of the platelet. Especially at the excitation wavelength of 633~nm, we can isolate a region in the center of the platelets where we find only contributions of SPPs which are launched by the tip and reflected at the edges. These signatures are used to determine the SPP wavelength of $\lambda_{SPP}=606$ nm in good agreement with theoretical predictions. Furthermore, we were still able to measure SPP signals after 20~$\upmu$m propagation, which demonstrates impressively the superior plasmonic quality of these mono-crystalline gold platelets.