Tunable plasmonic resonances in highly porous nano-bamboo Si-Au superlattice-type thin films

TL;DR

This paper presents the fabrication and optical characterization of highly porous, tunable nano-bamboo Si-Au superlattice thin films with strong anisotropic plasmonic resonances, demonstrating potential for sensitive water-based solvent detection.

Contribution

It introduces a novel nano-bamboo superlattice fabrication method and explores its tunable anisotropic plasmonic properties for sensing applications.

Findings

Observation of a localized quadrupole-like plasmonic mode near gold subcolumns.

Ability to tune the quadrupole mode frequency within the near-infrared range.

Potential application as a highly porous plasmonic sensor with ppm sensitivity.

Abstract

We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. The superlattice-type columns resemble bamboo structures where smaller column sections of gold form junctions sandwiched between larger silicon column sections ("nano-bamboo"). We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous nano-bamboo structures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is observed in the vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like mode frequency within the near-infrared spectral range by varying the geometry of the nano-bamboo structure. In addition, coupled-plasmon-like and inter-band transition-like modes occur in the visible and ultra-violet spectral regions, respectively. We elucidate an example for the potential use of the nano-bamboo structures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water.