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Optimization of the signal-to-background ratio for anodic aluminum oxide based surface-enhanced Raman scattering substrate
surface-enhanced raman scattering
anodic aluminum oxide
In the past, the anodic aluminum oxide template combined with metallic nano-particles have been one of popular designs for the enhancement of Raman scattering signal. Generally, the coupling of the electric dipole resonances among nanoparticles was applied to create strong near-field intensity, the so-called “hot spot” for surface-enhanced Raman scattering (SERS) substrate. Despite of SERS signal enhancement, a broadband background continuum, arisen from the penetration field inside the nanoparticles, was commonly observed and deteriorates the signal-to-background (S/B) ratio. In this thesis, we thoroughly investigate the near-field features of the plasmonic resonances by changing the diameters of silver nanoparticles and gap size. Their effects on the SERS enhancement, background value and S/B ratio were studied by considering both the local field amplification and ensemble-average effect. In addition, a double resonance substrate comprising of silver nanoparticles on periodic gratings was developed to further enhance both the near-field enhancement and the S/B ratio. A systemic study of the effect of the grating modulation depth, period, and the thickness of anodic aluminum oxide were performed to optimize the coupling of localized surface plasmon and surface plasmon polaritons for achieving higher S/B ratio. The double resonance substrate reaches 2.7 times enhancement of S/B ratio than the planar SERS substrate.
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