Epitaxial oxide thin films are used in many technologically important device applications. This workdeals with the deposition and characterization of epitaxial WO3 and SrBi2Ta2O9 (SBT) thin films onsingle crystal oxide substrates. WO3 thin films were chosen as a subject of study because of recentfindings of superconductivity at surfaces and twin boundaries in the bulk form of this oxide. Highlyepitaxial thin films would be desirable in order to be able to create a device within a film withoutpatterning it, by locally creating superconducting regions (e.g. twins) within an otherwise defect freefilm by reducing or doping the film with Na. Films were deposited by reactive magnetron sputteringat various temperatures on single crystal SrTiO3 (100) and R-sapphire substrates. X-ray diffractionstudies showed that the optimised films were highly (001) oriented, quality of epitaxy improving withdecreasing deposition temperature. AFM studies revealed columnar growth of these films. Films wereheat treated with Na vapour in order to reduce or dope them with Na. Low temperature measurementsof the reduced films did not show existence of any superconductivity.SBT is a ferroelectric oxide and its thin films are attractive candidates for non-volatile ferroelectricrandom access memory (FRAM) applications. High structural anisotropy leads to a high degree ofanisotropy in its ferroelectric properties which makes it essential to study epitaxial SBT films ofdifferent orientations. In this study, SBT films of different orientations were deposited on differentsingle crystal substrates by pulsed laser ablation. Highly epitaxial c-axis oriented and smooth SBTfilms were deposited on SrTiO3 (100) substrates. AFM studies revealed the growth of these films by3-D Stranski-Krastanov mode. However, these films did not exhibit any ferroelectric activity. Highlyepitaxial (116)-oriented films were deposited on SrTiO3 (110) substrates. These films were also verysmooth with root mean square (RMS) roughness of 15-20 Å. Films deposited on TiO2 (110) werepartially a-/b-axis oriented and showed the formation of c-axis oriented SBT and many impurities.Completely a-/b-axis oriented SBT films were deposited on LaSrAlO4 (110) substrates. Filmsdeposited at non-optimal growth temperatures showed the formation of many impurities. Attemptswere also made towards depositing Sr2RuO4 films on LaSrAlO4 (110) substrates, which can act as abottom electrode for ferroelectric SBT films.
Materials Science and Metallurgy, University of Cambridge 2001
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