Development Of Synthesis Routes For Epitaxial Oxide Thin Films

Using the deposition method best suited for depositing an oxide thin film can be the difference between measuring the intrinsic properties of the thin film and measuring extrinsic properties arising from defects, impurity phases, and contamination. In this work, unique synthesis routes for the deposition of three epitaxial oxide thin films is presented. Applying these new routes, new material properties were able to be discerned that had been concealed in thin films deposited utilizing conventional methods. Dual off-axis RF sputtering of Bi-rich BiFeO3̳ targets was employed to deposit a 1 [mu]m-thick multiferroic BiFeO3̳ film on various (111)p̳c̳-orientated substrates with cubic and orthorhombic symmetries. Using non-resonant x-ray magnetic scattering (NXMS) and neutron diffraction, the magnetic domain populations in the BiFeO3̳ were measured. We found that growing on reduced-symmetry substrate NdGaO3̳ (011)o̳, yields a BiFeO3̳ film with a single ferroelectric, structural, and magnetic domain consistent across the whole sample. The single domain remains stable even after switching a region of the sample ferroelectrically up to 10,000 times. Using NXMS polarimetry we confirm that there is a change in the magnetic polarity of the BiFeO3̳ domain after ferroelectric switching, demonstrating the coupling of the magnetic and ferroelectric orders in monodomain (111)p̳c̳-orientated BiFeO3 ̳ thin films. Using reactive RF sputtering of a pure Fe target, phase pure deposition of antiferromagnetic insulator [alpha]-Fe2O3̳ was achieved. SQUID magnetometry confirms the absence of any ferromagnetic minority domains in the film. We showed that the Morin transition temperature, above which [alpha]-Fe2̳O3̳ has a weak canted moment, decreases when reducing the thickness of the film. For films 10 nm and thinner, the Morin transition was suppressed completely. Using the XMLD contrast of the 10 nm-thick [alpha]-Fe2̳O3̳ film, X-ray Photoemission Electron Microscopy (PEEM) measurements uncovered a complex mosaic of sub-micron size antiferromagnetic domains connected by a network of antiferromagnetic spin vortices. The vortices were mostly found in vortex/antivortex pairs which could be annihilated through the application of an external magnetic field. When a 1 nm-thick Co layer was overlayed, the mosaic of domains present in the [alpha]-Fe2̳O3̳ was coupled to the Co which takes on the same mosaic pattern. Pulsed laser deposition of SrO and chemical vapor deposition of a TiO2̳ precursor gas were used simultaneously to deposit high quality SrTiO3 thin films in a hybrid deposition technique we called metal-organic pulsed laser deposition (MOPLD). We demonstrated a conductive 2-dimensional electron gas (2DEG) at the interface between MOPLD-grown SrTiO3 and PLD-grown LaAlO3̳, indicative that the SrTiO3̳ thin film is highly stoichiometric. The increased stoichiometry control afforded by MOPLD also grants the ability to control the point defects in the system. By decreasing the abundance of point defects, quantum properties of SrTiO3̳ become accessible.