The behaviour of the plasmonic modes of supported strongly coupled silver nanocubes is studied. Silver nanocube monolayers with controlled particle density were fabricated via the Langmuir-Blodgett technique and deposited on substrates with varying refractive indices. Substrates include glass, thin films of silicon, and titanium oxide on glass. The dipolar and bonded dipolar modes are red shifted with increasing refractive index of the substrate. Surface-enhanced Raman spectroscopy (SERS) is used as a tool to probe the electric field enhancements of the silver nanocube monolayers. SERS enhancement of silver nanocube monolayers is found to be highly substrate dependant, typically decreasing with increasing refractive index of the underlying substrate. This work aims to find the source of this enhancement decrease, and distinguishes between effects related electromagnetic enhancement and effects caused by the optics of the Raman spectroscopy system itself.
In the present work we investigated the properties and behavior of plasmonic modes of silver nanocube monolayers with
respect to reflection and transmission of visible radiation. Uniform monolayers of low particle densities were created
using the Langmuir-Blodgett technique using the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) as a
passive spacer. Dipole-dipole coupling modes were avoided by depositing at low pressures to ensure sufficient spacing
between the nanocubes. The refractive index sensitivities of plasmonic modes for monolayers on glass, silicon thin
films, and bulk silicon wafers were measured using varying solutions of water and ethylene glycol. By varying the
refractive index of the substrates it is possible to investigate the relative contribution of plasmonic modes with respect to
absorption of the incident signal.
Plasmonic properties of monolayers of strongly interacting silver nanocubes (AgNC) with controlled interparticle spacing are investigated. Uniform monolayers with controlled particle densities are made using the Langmuir-Blodgett
technique with passive phospholipid spacers, such as dioleoyl phosphatidylcholine (DOPC). Both extinction intensity
and wavelength of dipole-dipole coupling modes are tuned via particle spacing. The refractive indices of the substrates are used to tune dipolar and interparticle coupling modes via deposition onto thin films of silicon (0 - 25nm). By varying silicon film thickness it is possible to shift and control peak widths and position for both the dipole and interparticle dipole-dipole coupling modes. Control of plasmon shifts and interparticle spacing is applied towards the optimization of SERS substrates. SERS substrates using a Rhodamine B label are tuned at different excitation wavelengths which are in resonance with either the plasmon dipole, fluorescent dye, or interparticle coupling mode. Substrates display reproducible enhancement across multiple sites. This work presents methodology to design and optimize uniform silver nanocube SERS substrates through tuning of plasmon shifts and particle spacing.