Plasmonic substrates for Surface Enhanced Raman Scattering

Due to their favorable optical properties, nanostructures supporting surface plasmons have attracted considerable attention for a broad range of applications. Surface enhanced Raman scattering is one of the most important applications of plasmonic structures. In this thesis, the optical properties of plasmonic structures based on periodic nanoparticle arrays are investigated. New SERS substrates are developed that take advantage of the properties of these structures. It is demonstrated that the substrates can provide average SERS enhancement factors of nearly 109.;The introduction of surface plasmon polariton (SPP), localized surface plasmon (LSP), Raman scattering and surface enhanced Raman scattering (SERS) are examined in Chapter 1.;Chapter 2 demonstrates that coupling between grating diffraction and localized surface plasmons in two-dimensional gold nanoparticle arrays in water leads to narrow near-infrared resonance peaks in measured far field extinction spectra. Good agreement is obtained between Finite Difference Time Domain (FDTD) calculations and experimental extinction spectra. The FDTD calculations predict that the gold nanoparticle arrays exhibit near-field electric field intensity (|E|²) enhancements approximately one order of magnitude greater than those of single isolated gold nanoparticles.;In Chapter 3, the interaction between localized and surface plasmons polariton is investigated in a structure consisting of a two-dimensional periodic gold nanoparticle array, an SiO2 spacer and a gold film. The resonance wavelengths of the two types of surface plasmons supported by the structure are tailored by changing the gold nanoparticle size and the array period. An anti-crossing of the resonance positions is observed in the reflection spectra, demonstrating the strong coupling between localized and propagating surface plasmons. This strong coupling is described by a classical coupled oscillator model in Chapter 4. The effects of the particle density, the particle size and the SiO2 spacer thickness on the coupling strength are experimentally investigated. It is demonstrated that by tuning the geometrical parameters of the double resonance substrate, one can readily control the resonance frequencies.;The SERS performance of a double resonance plasmonic substrate consisting of a two-dimensional periodic gold nanoparticle array, an SiO2 spacer and a gold film is characterized in Chapter 5. The largest SERS enhancement factor for a gold device is measured to be 7.2x107, which is more than two orders of magnitude larger than that measured on a gold nanoparticle array on a glass substrate. The largest SERS enhancement we achieve is 8.4x10 8, and obtained using a silver device.;In Chapter 6, the angular effects on the local field enhancement and the Raman emission enhancement are investigated on the double resonance SERS substrate numerically and experimentally. It is found that the local field enhancement is very sensitive to the incident angle and the Raman emission enhancement has a strong angular dependence on the detection direction. It is demonstrated that a stronger SERS signal results when the double resonance substrate is illuminated with a collimated, rather than focused, laser beam.