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Title page for ETD etd-11042009-100728


Type of Document Dissertation
Author Halabica, Andrej
URN etd-11042009-100728
Title Coherent acoustic phonons in metal/dielectric superlattices
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Richard Haglund Committee Chair
Norman Tolk Committee Member
Robert Magruder Committee Member
Sharon Weiss Committee Member
Sokrates Pantelides Committee Member
Keywords
  • laser annealing
  • superlattice
  • coherent acoustic phonons
  • surface modes
  • nanoparticles
Date of Defense 2009-10-27
Availability unrestricted
Abstract
Pulsed infrared laser annealing experiments on metal implanted

dielectric matrices were performed, using a free electron laser as a

source of infrared radiation at 8 and 9 *m wavelengths. This was

the first study where such wavelengths were used for laser annealing

of composite materials. Our results show that the annealing

successfully modified nanocomposites consisting of Au and Ag

nanoparticles embedded in a dielectric matrix. Fast nucleation and

growth of Au nanoparticles in both SiO2 and Al2O3 matrices

were observed, while nanoparticle dissolution due to this rapid

thermal annealing process was observed in Ag-implanted SiO2.

These experiments demonstrate the unique effects of fast thermal

heating of the matrix on the size and size distribution of embedded

metal nanoparticles, using photons with energies far below the bulk

bandgap of the matrix.

A set of composite materials in the form of Au/Al2O3

superlattices was also prepared using electron beam evaporation.

Time-resolved femtosecond laser spectroscopy was successfully

applied to study the vibrational properties of these multilayers. A

comprehensive experimental and computational study of the effects of

varying Au layer thickness on the excitability and detectability of

the first and second surface acoustic phonon mode was undertaken.

The frequency of these modes was compared to the theoretical

calculation and the slight differences were attributed to the effect

of the nanoparticle structure of the Au films, which was confirmed

using TEM and optical spectroscopy. In addition to the surface

modes, propagating phonon modes were observed in the Au(5

nm)/Al2O3(45 nm) superlattice. These belong to the lowest

minibranch of the zone-folded longitudinal phonon dispersion curve

and travel in the form of a propagating pulse, which is reflected at

the substrate and surface interfaces. By detecting two echoes of the

pulse, it was possible to experimentally determine the effective

sound velocity in the superlattice.

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