Date of Award

8-25-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Tar-Pin Chen

Abstract

Epitaxial thin film growth and characterization of cuprate oxide insulating materials has been motivated by scientific importance and technological need of these materials for various applications including the nanofabrication of high-Tc trilayer Josephson junction and electronics. For this purpose, we fabricated epitaxial and device-quality (110)-oriented PrBa2(Cu1-xMx)3O7 (x=0.2, M= Ga, Al, Fe, Co, Ni, and Zn) (PBCMO) thin films using excimer pulsed laser deposition technique and conducted systematic studies of the effects of various metals substitution for copper atoms at two different sites of the PrBa2Cu3O7 (PBCO) structure using various characterization techniques including the x-ray diffraction, atomic force microscopy, temperature dependent electrical resistivity measurements, and Raman spectroscopy. Our temperature dependent electrical resistivity measurements have revealed a tremendous increase of the resistivity in (110)-oriented Ga and Al doped PBCO thin films compared to undoped or Zn and Ni doped PBCO thin films at low temperatures demonstrating a much better insulation for the fabrication of YBCO based tunneling Josephson junctions. Electrical transport studies in Ga and Al doped PBCO thin films have shown existence of hopping conduction between the localized states following Mott's three-dimensional variable-range hopping at low temperatures that extends up to the room temperature. Extensive localization of charge carriers has been found to occur with a decrease of the localization length and an increase of activation energy for hopping due to the incorporated Ga and Al dopants. Many interesting results have been obtained in the Raman scattering studies of (110)-oriented PBCMO thin films. Two significant results have been observed in Ga and Al doped thin films: first, a downward shift in Raman phonon mode corresponding to the stretching vibration of apical oxygen against the stationary Cu(1) atom compared to the same Raman mode in PBCO , second, emergence of an additional Raman mode related to a disorder due to symmetry breaking in Cu-O chains. The much higher electrical resistivity, downwards shift of apical oxygen Raman mode of PBCO, and an emergence of the disorder related Raman vibrational mode in Cu-O chains indicated the substitution of Cu(1) atoms with Ga and Al atoms in the PBCO structure.

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