Tunable plasmonic resonances in Si-Au slanted columnar heterostructure thin films

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. We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous Si-Au slanted columnar heterostructures. 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 Si-Au slanted columnar heterostructures. 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 Si-Au slanted columnar heterostructures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water.

Broadband Enhanced Chirality with Tunable Response in Hybrid Plasmonic Helical Metamaterials

“…The main fabrication problems with the GLAD process are the anisotropic broadening growth, also known as fanning or shadowing effect, column bifurcation in the growth procedure, and competition between adjacent columns. [ 32,51–53 ] By using the generalized Mueller matrix spectroscopic ellipsometry technique that takes into account both transmitted and reflected waves, we successfully measure (using Equation (2) in Section 4) the spectral evolution of the Kuhn's g‐ factor for the RH Si helical metamaterial. The resulted broadband strong chiroptical response with a maximum value around ≈3 eV is seen in Figure 1d, clearly proving that the presented helical metamaterials have a pronounced optical chirality.…”

“…The S‐parameters, also known as scattering parameters, are computed by using the multiple port definition. [ 32 ] The cross and co‐polarized transmittance and reflectance coefficients were calculated from the obtained scattering parameters. The derived total reflectance and transmittance values contain both cross and co‐polarized components.…”

“…This discrepancy is more pronounced for multi-segment elongated helical metamaterials and is a direct consequence of the GLAD fabrication imperfections, in particular the fanning/shadowing effect, bifurcation in the growth procedure, and competition between adjacent very closely packed helices. [32], [51]- [53] Hence, the structural disorder increases for larger segment number, which results to higher overall effective absorption from the experimentally obtained elongated helical metamaterials that, in turn, reduces the absorptionbased measured chiral g-factor.…”

“…The glancing‐angle deposition (GLAD) technique is used to fabricate these unique structures, which is an emerging bottom‐up fabrication approach that is free of masks or templates and permits free choice of materials incorporated into 3D nanostructures. [ 31,32 ] Notably, the chiroptical properties of various 3D nanostructures such as crescent, [ 33 ] pillar, [ 34 ] gammadion, [ 35 ] sphere, [ 36 ] and helical [ 37–48 ] were investigated in the literature at different frequency ranges than the visible/UV or by using alternative more complicated fabrication techniques. Unlike all previous relevant works based on GLAD, [ 42–48 ] here we present a unique bottom‐up technique to achieve subsequent deposition of different dielectric (silicon/Si) and metallic (silver/Ag) materials leading to hybrid plasmonic helical metamaterials with a multiple number of subsegments and helices (as shown in Figure a) that achieve tunable chirality.…”

Size and shape control of a variety of metallic nanostructures using tilted, rotating evaporation and lithographic lift-off techniques

“…Finally, despite using metallic physical vapour deposition here as a proof-of-concept demonstration, in principle any evaporative material or indeed combinations of materials—e.g. to form evaporated heterojunctions 61 having a specific shape—could be used to form such features.…”