Date of Award

Fall 2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Federated Physics Department

First Advisor

Andrei Sirenko

Second Advisor

Daniel-Dennis McAlevy Bubb

Third Advisor

John Francis Federici

Fourth Advisor

Leonid Tsybeskov

Fifth Advisor

Trevor Tyson

Sixth Advisor

Tao Zhou

Abstract

The following dissertation applies synchrotron radiation-based characterization techniques to the fields of gallium nitrides, multiferroic manganites, and self-assembled nano-domain oxide films. These material systems were chosen due to their unusual properties and potential device applications, which have made them very attractive to the scientific community.

Synchrotron-based High Resolution X-ray Diffraction (HRXRD) was used to characterize the structural properties of GaN-based multiple quantum well (MQW) structures grown on trapezoidal shaped GaN ridges. Results where interpreted within the framework of vapor-phase diffusion and surface-migration effects during the metalorganic vapor phase epitaxial growth. The relatively short diffusion length of group- III precursors and growth enhancement, due to facet migration was found to have significant effects on the MQW formation.

The use of synchrotron based HRXRD and in particular cross-sectional reciprocal space mapping (RSM) was then extended to studying the intriguing structural properties of a ZnMnGaO4 film epitaxially grown on MgO (001) substrate. The results of this study helped in identifying the ZnMnGaO4 film, as consisting of a self-assembled nano- checkerboard structure of highly aligned and regularly spaced vertical nanorods. The results demonstrated the importance of lattice distortion symmetry at the phase boundaries as a means for the coherent coexistence of two domain types within the film volume.

Synchrotron-based far-infrared spectroscopy was performed at low temperatures on the single crystal multiferroic manganite HoMn2O5. A number of the infrared-active excitations were attributed to electric-dipole transitions between ligand-field split states of Ho3+ ions. It is proposed that the proximity in energy between magnons and Ho3+ ligand fields (LF) might connect the magnetism and dielectric properties of this compound through coupling with the Mn spin structure.

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