Design and Characterization of Plasmonic Absorbers Based on Gold Nano-spheres

Abstract: Noble-metal-based nanostructures can exhibit strong localized plasmon resonance at optical frequency, which leads to efficient plasmonic light absorbers. Such an artificially engineered absorber can have potential applications in sensing, cancer diagnosis and therapy, and photovoltaic cells etc. This thesis systematically studies a particular class of plasmonic absorber based on gold nanoparticles deposited on top of a continuous gold substrate. In our case studies, the nanoparticles have sub-wavelength sizes of less than 50 nm; their reflectances are examined over 400-800 nm light wavelength range. With a 3D finite-element method, we identified that the resonance at especially a long-wavelength position originates not from dipole resonance of the particles, but from the inter-particle near-field coupling resonance. The influences of particle size, particle shape, inter-particle distance, particle-substrate spacer, particle lattice, number of particle layers etc on the resonance are studied thoroughly. Experimentally, an absorber based on chemically-synthesized Au@SiO2 core-shell nanoparticles was fabricated. Measurement shows that the absorber has a characteristic absorption band around 800 nm with an absorbance peak of 90%, which agrees surprisingly well with our numerical calculation. The fabrication technique can be easily scaled for devising efficient light absorbers of large areas.