In this study, optical behavior of metal nanoparticles having dimensions smaller
than the wavelength of visible light is studied experimentally and numerically.
Gold (Au) and silver (Ag) nanoparticles are studied due to their superior optical
properties when compared to other metals. A compact code based on Discrete
Dipole Approximation (DDA) is developed to compute extinction efficiencies of
nanoparticles with various different properties such as material, dimension and
geometry. To obtain self consistent nanoparticle arrays with well defined
geometries and dimensions, Electron Beam Lithography (EBL) technique is
mainly used as the manufacturing method. Dose parameters required to produce
nanoparticles with dimensions down to 50 nm over substrates with different
electrical conductivities are determined. Beam current is found to affect the doseV
size relation. The use of thin Au films as antistatic layer for e-beam patterning
over insulating substrates is considered and production steps, involving
instabilities due to contaminants introduced to the system during additional
removal steps, are clarified. 4 nm thick Au layer is found to provide sufficient
conductivity for e-beam patterning over insulating substrates. An optical setup
capable of performing transmittance and reflectance measurements of samples
having small areas patterned with EBL is designed. Sizes of the metal
nanoparticles are determined by scanning electron microscope (SEM) and spectral
data obtained using the optical setup is analyzed to find out the parameters
affecting the localized surface plasmon resonances (LSPR). Arrays of particles
with diameters between 50 &ndash / 200 nm are produced and optically analyzed. Size
and shape of the nanoparticles are found to affect the resonance behavior.
Furthermore, lattice constants of the particle arrays and surrounding medium are
also shown to influence the reflectance spectra. Axes with different lengths in
ellipsoidal nanoparticles are observed to cause distinguishable resonance peaks
when illuminated with polarized light. Peak intensities obtained from both
polarizations are observed to decrease under unpolarized illumination. Binary
systems consisting of nanosized particles and holes provided better contrast for
transmitted light.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/3/12610934/index.pdf |
| Date | 01 September 2009 |
| Creators | Guler, Urcan |
| Contributors | Turan, Rasit |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | Access forbidden for 1 year |
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