Date of Award

8-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Ramki Kalyanaraman

Committee Members

Jon Camden, Gerd Duscher, David Mandrus, Philip Rack

Abstract

Synthesis of well-defined nanostructures by pulsed laser melting is an interesting subject from both a funda- mental and technological point of view. In this thesis, the synthesis and functional properties of potentially useful materials were studied, such as tin dioxide nanostructured arrays, which have potential applications in hydrogen gas sensing, and ferromagnetic Co nanowire and nanomagnets, which are fundamentally im- portant towards understanding magnetism in the nanoscale. First, the formation of 1D periodic tin dioxide nanoarrays was investigated with the goal of forming nanowires for hydrogen sensing. Experimental obser- vations combined with theoretical modeling successfully explained the mechanisms of structure formation. One of the primary findings was that evaporation of tin dioxide was the most significant contributor to the pattern formation. Next, the spontaneous liquid film spinodal dewetting process under pulsed laser melting was modeled using the viscous dissipation approach. We found that the fluid condition for spinodal dewet- ting is where the film-substrate tangential stress is zero. Following this, the remainder of the thesis focused on synthesis and characterization of magnetic nanostructures. We first successfully installed a home-built Surface Magneto-optical Kerr Effect (SMOKE) system. Using SMOKE we measured the Kerr rotation from potential plasmonic-ferromagnetic magneto-optical materials made from Co-Ag thin films and nanoparti- cles as a function of composition. We found that films made by co-deposition of Co and Ag showed higher Kerr rotation in contrast to bilayer film structures with same effective amount of Co and Ag. Next, we inves- tigated the shape and size dependence of magnetic properties of nanostructures, specifically hemispherical nanoparticles, nanowires and nanorods, prepared by the pulsed laser process. The magnetic anisotropy was studied by using the SMOKE system complemented with magnetic force microscopy (MFM) analy- sis. Results from magnetic hysteresis measurements of the nanostructures in different geometries showed coercivity and remanence that could be attributed to magnetic shape anisotropy. MFM analysis showed that domain orientation was found to depend on the aspect ratio of the nanostructure. These investigations generally helped advance the science of nanostructure synthesis using nanosecond pulsed laser techniques as well demonstrate that SMOKE is a promising method to investigate nanostructure magnetism.

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