Reflection and Absorption Spectra of Silver Nanocubes on a Dielectric Substrate: Anisotropy, Angle, and Polarization Dependencies

Angle and polarization dependent UV–visible reflection and transmission spectra were measured for monolayers of weakly interacting silver nanocubes (of 40 and 80 nm edge lengths) supported by thin films of titanium oxide on glass utilizing both front and rear geometries with respect to the incident radiation. The supporting substrate mediates the hybridization of dipolar and quadrupolar plasmon resonances. From the spectra absolute extinction and absorption cross sections for supported silver nanocubes were determined. A strong angle dependence of the extinction and reflection spectra for p- but not s-polarized light was observed. This dependence is considerably more pronounced for the hybridized quadrupolar resonance of the 40 nm cubes. When illuminated from the rear, a significantly stronger absorption of light by the dipolar but not the quadrupolar resonance occurs for both cube sizes. Such absorption anisotropy could result from the wavelength dependent constructive or destructive interference between incident and scattered light from the nanocubes. This study demonstrates the impact of a dielectric substrate on the optical properties of novel plasmonic materials.