Content:
When illuminated with visible light, nanostructured noble metals exhibit a strongplasmon resonance at wavelength, p, that has been shown to be sensitive to its size,structure, the dielectric properties of the surrounding medium, and charge density. Thetunability of the plasmon resonance has allowed metal nanosystems to be fabricated withresonances matching the solar spectrum for us in plasmon promoted catalysis, plasmonicphotovoltaics, and surface-enhanced raman spectroscopy. Here we use UV-Visible spectroscopyto track the shifts of the plasmon resonances from an array of gold nanoparticlesburied under metal oxide layers of varying thickness when in contact with one of two bulkmetals: aluminum or silver. By assuming the array of gold nanoparticles and metal-oxidelayers to be an optically homogenous lm of core-shell particles on a substrate, we developeda Maxwell-Garnett effective medium approximation to extract reliable opticalparameters for the gold nanoparticles, yielding their charge state before and after contactwith the bulk metal.Based on the optical parameters extracted from our model, we nd the magnitude ofcharge transfer from the bulk metal to the gold nanoparticle is independent of the workfunction of the bulk metal. Furthermore, when gold is used as the bulk layer in contactwith the gold nanoparticles, we measured an appreciable amount of charge transfer to thegold nanoparticles, failing to support the well-established model for electrostatic contactelectrication. Instead, we attribute the charge transfer to the so called plasmoelectriceffect, an optically induced charge transfer mechanism, in which the gold nanoparticlemodifes its charge density to allow its resonant wavelength to match that of the incidentlight. We show, however, that in our devices the Schottky barriers between the metalsand the metal oxide layers create a rectication effect that favors electron transfer fromthe bulk metal to the nanoparticles over the reverse effect.
Note:
Dissertation eScholarship, University of California 2017
Language:
English
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