43258-G5
Fundamental Studies of Epitaxial Nucleation and Growth of Conductive-Oxide Thin Films on Highly Reactive, Single-Crystal-Like Textured Metal Substrates
In the course of our research, exciting challenges in the development of high-temperature superconducting tapes have lead to a re-direction of our goals. We have investigated the deposition and growth characteristics of LaMnO3 films directly on ion beam assisted deposition (IBAD) of MgO templates. The latter are being used in pre-commercial high temperature superconducting (HTS) wire architectures, where it is well understood that integrity of the cap buffer layer is crucial for epitaxial growth of subsequent HTS coatings. It is also equally important and desirable to minimize the number of buffer layers to reduce the overall process complexity. One way to achieve a simplified IBAD architecture is to eliminate the need for the homo-epitaxial MgO layer and to deposit high quality epitaxial cap layers directly on IBAD-MgO templates. Note that, due to the damage caused in MgO lattice during the IBAD processing, homo-epitaxial MgO was previously used to ensure the structural robustness of IBAD-MgO by further improving the texture and restoring the surface lattice constant to that of the bulk MgO (0.421 nm). In this work, we have studied various rf-magnetron sputter growth parameters/conditions for epitaxial growth of LMO layers directly on IBAD (MgO) without homo-epi MgO layers. Results showed that while epitaxial growth of LMO can be achieved in a variety of sputtering gas mixtures, the deposition temperature has a strong effect on the crystalline quality of these films. The performance of the developed LMO/IBAD(MgO) templates is qualified by characterizing the superconducting properties of 1 µm-thick YBCO coatings deposited by pulsed laser deposition (PLD). In addition, we varied the LMO layer thickness from 30-240 nm to determine the optimum YBCO performance. Electrical transport properties of 1 µm-thick PLD YBCO films on the simplified LMO/IBAD-MgO architecture showed similar (if not better) performance, compared to those films deposited on templates having homo-epitaxial MgO layers. More importantly this result is found to be independent of the LMO thickness, which was varied from 30-240 nm in the present study. Finally, this investigation underscores the strong potential of LMO as a single cap layer directly on IBAD(MgO) and may open a pathway for the fabrication of more efficient, robust and lower cost IBAD-based second generation HTS wires.
