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Epitaxial YBa2Cu3O7−x Thin Films: Scanning Tunneling Microscope Study of the Initial Stages of Epitaxial Growth, Growth Mechanism, and Effects of Substrate Temperature

Published online by Cambridge University Press:  21 February 2011

Shen Zhu
Affiliation:
Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996
Douglas H. Lowndes
Affiliation:
Solid State Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831–6056
X.-Y. Zheng
Affiliation:
Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831–6123
David P. Norton
Affiliation:
Solid State Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831–6056
R. J. Warmack
Affiliation:
Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996 Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831–6123
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Abstract

The surface microstructure of epitaxial YBa2Cu3O7−x films grown by pulsed laser ablation on (001) MgO and SrTiO3 substrates has been studied at various growth stages, ranging in thickness from eight c-axis perpendicular unit cells to ∼220 nm. On MgO (lattice mismatch ∼9%) even the thinnest films grow unit cell-by-unit cell by an island growth mechanism. However, on SrTi03 (mismatch ∼1%), a transition from a layer-like growth mode to island growth is observed as the film thickness increases. Islands with clear spiral growth structures are observed in even the thinnest films on MgO, but for films grown on SrTiO3 the spiral growth features are found only for film thicknesses slightly greater than the critical thickness for the switch to an island growth mode. The islands consist of stacks of atomically flat terraces whose step heights are multiples of the c-axis lattice parameter. The island density decreases significantly with increasing film thickness, while their diameters range from 50–400 nm, increasing with growth temperature. The terraced island grain morphology causes a surface roughness of from 10 to 30 nm (depending on growth temperature) in films ∼200 nm thick.

Type
Research Article
Copyright
Copyright © Materials Research Society 1992

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