Plasmonic nanomaterials for midinfrared and their photomodification
Abstract
Semicontinuous metal films (SMFs) have been studied for several decades due to their unique optical properties. These films support the collective oscillations of conduction electrons, surface plasmons (SP) that can be excited by light in a metal structure. The SP resonance frequencies depend on the type of metal, the nanostructure geometry, and the surrounding medium. Plasmonic nanostructures act like optical nanoantennas. They can accumulate and build up electromagnetic energy in nanometer-scale areas called "hot spots". This energy buildup results in high local fields and thus can produce a dramatic enhancement of optical responses. Materials supporting SP resonances can be used for applications such as surface-enhanced Raman spectroscopy with sensitivity high enough to enable single molecule detection, surface-enhanced infrared absorption, data recording, harmonic generation, absorption elements in solar cells and others. In this work we have studied the optical properties of plasmonic nanostructures in the visible and mid-IR range. The samples studied include e-beam evaporated SMFs and chemically synthesized core-shell metal-dielectric structures. Both sample types have fractal nanostructures with broad absorption bands extending from the UV to the midinfrared range. Laser photomodification processes on these metal-dielectric structures were studied. The induced changes in extinction of both types of studied structures are wavelength- and polarization-selective. Mid-IR long-pass filters have been fabricated using SMFs and their subsequent photomodification with picosecond and nanosecond pulsed lasers operating in the mid-IR. Additional experiments on the photomodification of gold nanostructures grown on silica microspheres have been performed and show promising results, similar to those obtained with planar structures.
Degree
Ph.D.
Advisors
Drachev, Purdue University.
Subject Area
Electrical engineering|Optics
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