An ultra-broadband wavelength-selective anisotropic plasmonic metasurface

We offer and demonstrate a new type of plasmonic metasurface for sensorics and surface-enhanced Raman spectroscopy (SERS) spectroscopy, characterized by a wide spectral range of sensitivity from 450 nm to 850 nm. The metasurface is formed by Ag nanoparticles of different sizes. The metasurface has clear anisotropy formed by the Ag nanoparticles' size-dependent plasmonic resonances. The resonant wavelength of the metasurface is linearly changed in one direction on a metasurface realizing a wavelength to space conversion and remains the same in the other direction. The metasurface has advantages for use in different applications of optical microscopy and SERS diagnostics, since it simultaneously provides a strong optical signal amplification of up to 4 × 107 as well as a wavelength to space conversion with a 10 nm spectral resolution. We show the fabrication of the anisotropic plasmonic metasurface by the use of a robust approach based on Ag nanoparticle self-assembly during a molecular-beam-epitaxy growth process. We demonstrate an application of the metasurface for the fluorescence detection of low concentrations of dye molecules (Cy-7.5) and the surface-enhanced Raman spectroscopy of an organic molecular monolayer (Alq3).