Integration of nanoparticles into thin films is essential for the development of functional materials, studies of fundamental interfacial processes, and exploitation of inherent properties from the particles themselves. In this work, we systematically investigate the process of incorporation of silver nanocubes into thin polystyrene films at temperatures just above the polymer glass transition. The process of nanocrystal incorporation can be precisely monitored via far-field spectroscopy to observe the response of spatially resolved hybrid plasmon modes. Each plasmon resonance has a distinct dynamic range and maximum sensitivity forming a complementary set of nanorulers that operates over a distance comparable to the edge length of the cubes. The approach explored in this work is a general robust method for the development of long-range polychromatic nanorulers.

The refractive index (RI) sensitivity of extinction spectra was compared experimentally for silver nanocubes in solution and in supported monolayers prepared by the Langmuir technique. The size of the nanocubes, RI of supporting dielectric substrate, and monolayer surface pressure were used as variables in refractive index sensing optimization. The dipolar plasmon modes of the colloidal nanocubes were found to have the highest RIS values of 176, 361, and 480 nm/RI units for 40, 80, and 130 nm cubes, respectively. The largest figure of merit (FOM) of 4.55 was measured for a quadrupolar mode of 130 nm nanocubes. When compared to suspensions, the refractive index sensitivities (RIS) of supported nanocubes were reduced by ∼50% and decreased with increasing monolayer surface pressure. The RIS of 40 nm cube monolayers appeared to be sensitive to the substrate RI due to the RI-dependent plasmon mode hybridization, resulting in dipolar and quadrupolar modes. The intensity of this quadrupolar peak was found to increase with the angle of incident light. This work shows that the use of high refractive index dielectric substrates, a passive molecular spacer, and large angles of incidence can improve the detection of plasmonic response by supported nanocube monolayers.

A novel technique for increasing the sensitivity of tilted fibre Bragg grating (TFBG) based refractometers is presented. The TFBG sensor was coated with chemically synthesized silver nanowires ~100 nm in diameter and several micrometres in length. A 3.5-fold increase in sensor sensitivity was obtained relative to the uncoated TFBG sensor. This increase is associated with the excitation of surface plasmons by orthogonally polarized fibre cladding modes at wavelengths near 1.5 μm. Refractometric information is extracted from the sensor via the strong polarization dependence of the grating resonances using a Jones matrix analysis of the transmission spectrum of the fibre.

Plasmonic properties, such as refractive index sensitivity (RIS), surface enhancement of the Raman signal (SERS), fluorescence quenching, and photocatalytic activity, of monolayers of weakly interacting monodisperse silver nanocubes were qualitatively modified in a very well controlled manner by supporting them on thin silicon films with varying thickness. Such fine tunability is made possible by the strong dependence of the nanocube dipolar (D) and quadrupolar (Q) plasmon mode hybridization on the refractive index of the supporting substrate. By increasing the Si film thickness from zero to ~25 nm we were able to "shift" the D resonance mode by up to 200 nm for ~80 nm cubes without significantly affecting the Q mode. The silicon supported nanocubes showed a significant improvement in RIS via the Q mode with a figure of merit greater than 6.5 and about an order of magnitude enhancement of the SERS signal due to the stronger electric field created by the D mode. Such substrates also showed a ~10 times decrease in rhodamine 6G fluorescence as well as the rates of amorphous carbon formation. The study proposes a new way to design and engineer plasmonic nanostructures.

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.