Optical properties of gold particles with near micron size: localized and propagating surface plasmons

摘要

This proceeding summarizes the optical properties of plasmonic structures from nanoscale to macroscale. Of particular interest, Au triangles and hole arrays of near micron size exhibit concomitantly surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) optical properties in the Vis-NIR region, resulting in excellent optical properties for biosensing. In transmission spectroscopy, 15 nm nanoparticles absorbs at λ = 525 nm, nanotriangles of > 200 nm edge length absorbs at λ > 600 nm while nanohole arrays exhibit a more complex spectrum including absorption and enhanced optical transmission (EOT) features. Nanohole arrays are also sensitive to refractive index (RI) change and it can be optimized by tailoring the hole diameter and the periodicity. Au triangles ranging from nano (200 nm) to micron size (1.5 μm) are active in LSPR with an absorption peak that redshifts with the increasing aspect ratio of the structure. In total internal reflection (TIR) experiment, Au triangles with an edge length of 500 nm or greater present an absorption peak at λ = 800 nm. Also, triangles of 700, 950 and 1800 nm have a maximum transmission around λ = 650 nm that is highly sensitive to refraction index (RI) variations. This absorption peak is attributed to propagating SPR, similarly to the optical phenomenon occurring on a smooth Au film as used in the Kretschmann configuration of SPR. Lastly, nanohole and microhole arrays spectra, measured in TIR, are a composite of both triangles (LSPR) and thin film spectra (SPR).