Local field enhancement of different core shell nano-particles placed over a substrate under an AFM tip

Abstract

Metal nanoparticles (NPs) interacting with the light in near-field undergoes lo calized surface plasmon resonance (LSPR) when the oscillating charges on the surfaces resonates with the incident light frequency. The EM wave illumination at resonance wavelength will result in field localization and absorption enhancement with localized heating. Absorption enhancement and LSPR wavelength of nanoparticles can be ana lyzed with the hybrid structures such as core-shell NPs made of dielectric and metals. The scope of thesis is the absorption behavior of core-shell NPs placed on a glass sub strate illuminated by total internal reflection,which creates surface evanescent waves. The near-field coupling of core-shell NP is analyzed by changing the material compo sitions at core and shell with different size configurations, which is called volumetric filling ratio of the core. The LSPR wavelength tunability and effective absorption effi ciency values of each pair are analyzed with respect to their size parameter. Moreover, the sensitivity study of bimetallic core-shell NPs to changes in the refractive index of the medium showed that increasing the dielectric medium refractive index can result in increase in field intensity and red-shift of the LSPR wavelengths. For the localized heating purposes, core-shell NPs are also considered with the AFM tip placed over the NP. For this, wave polarizations and tip materials are compared for the spectral absorption behavior of the NPs. It is shown that NPs can have multipeak resonance either with absorption enhancement or damping. Designated problems are numerically investigated by using an open source MATLABTM toolbox, which is the vectorized version of the discrete dipole approximation with surface interaction (DDA-SI-v).