Fano resonances in metal /Dielectric Composites and growth mechanism and ferromagnetism in ZnO Nanostructures
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Date
2017-06
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Addis Ababa University
Abstract
In this dissertation, we studied on the origin and physical mechanisms leading
to Fano resonances and scattering of light in metal /dielectric composites. The
properties of composite materials can be tuned by dielectric permittivity of host
matrix, volume fraction, geometry of the inclusion and distribution type. The theoretical
model consists of non-magnetic spherical and cylindrical nanoinclusions
which are embedded in non-absorbing host medium illuminated by plane waves
having uniform electric elds. The method employed treats the arrays of particles
within the framework of the conventional Rayleigh approximation. The electric
potential distribution of the composites having dielectric core, metal shell and host
matrices are systematically calculated. As such metal/dielectric nanocomposites
with careful arrangement can also support Fano like resonances, the underlying
mechanisms including their origin are discussed. We nd that Fano-like resonances
can occur at the same input volume fraction of the metal coated (p) provided the
dielectric function of active host medium ("00
h) has negative values. Such Fano-like
resonance are induced by interaction between dipolar modes of the inner core, and
multipolar plasmon modes of the coated shell. This provides potential application
in high performance surface-enhanced spectroscopy, electromagnetic induced
transparency, biosensing, plasmon line shaping, lasing and nonlinear switching. In
addition, the experimental section of the study in the thesis presents the growth
mechanism of ZnO with di erent morphologies. The e ect of dopant concentration
on the optical and magnetic properties has been studied. The role of precursor,
reaction temperature and the origin of ferromagnetism in Al doped ZnO has been
reported. ZnO nanostructures prepared using sol-gel and chemical bath deposition
are analyzed using di erent techniques. The nal product was analyzed using
such techniques as scanning electron microscopy (SEM), photoluminescence (PL)
spectroscopy (steady and temperature dependent), Ultra-violet visible (UV-Vis)
spectroscopy, Fourier transform infrared spectroscopy (FTIR), Electron paramagnetic
resonance (EPR), X-ray di raction (XRD) and Raman spectroscopy
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Keywords
Fano resonances in metal