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Molecular Beam Epitaxy of Oxide Thin Films

Darrell G. Schlom
Organization: The Pennsylvania State University
Journal / Anthology

Materials Science and Engineering

The discovery of a class of new layered crystalline materials which exhibit superconductivity at unprecedented temperatures has opened new possibilites for the future of electronic devices and for molecular beam epitaxy (MBE) as a potential method to grow device structures containing these materials. The low growth temperature and atomic layering capability that MBE has demonstrated for the growth of semiconductors suggests that the MBE growth of non-equilibrium layered structures and metastable phases within oxide systems encompassing the high transition temperature superconductors might be possible. If available, such a growth technique would be useful not only for device fabrication, but would offer an unparalleled technique to fabricate metastable superlattice mixtures to test high transition temperature theories, which might then allow the growth of even higher temperature superconducting compounds.

In contrast to the simplicity of the materials systems to which MBE has been successfully applied, the growth of fully oxidized, multi-element compounds by MBE involves significant challenges. This thesis describes research to develop in situ growth techniques allowing the growth of layered superconducting cuprates and related phases by MBE, and characterization of growth films. The conditions necessary to achieve this in situ ability, including the use of highly oxidizing species in order to maintain a long mean free path necessary for MBE, appropriate substrate temperature, precise composition control, and suitable substrates are discussed. The MBE apparatus used and design improvements made during the course of this research are described. The experimental results of films grown in the Dy-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems demonstrate the ability of this suttered, layer-by-layer MBE technique to grow smooth, layered, metastable compounds, including ordered superlattices, in situ using ozone. Both cross-sectional TEM images and a comparison of the observed x-ray patterns to limiting case simulations, show that this growth technique is effective in selecting between nearly energetically degenerate Bi2Sr2Ca(n-1)Cu(n)O(x) phases and layering them on a half unit cell by half unit cell basis.

*Science > Physics > Solid State Physics