AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1+EM-TuA

Paper SS1+EM-TuA3
Islanding, Facetting, and the Lattice Relaxation in the Growth of @alpha@-Fe@sub 2@O@sub 3@ on @alpha@-Al@sub 2@O@sub 3@

Tuesday, October 26, 1999, 2:40 pm, Room 606

Session: Oxides: Growth and Structure
Presenter: S.I. Yi, Pacific Northwest National Laboratory
Authors: S.I. Yi, Pacific Northwest National Laboratory
Y. Liang, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
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The growth of @alpha@-Fe@sub 2@O@sub 3@ on c- and r-oriented @alpha@-Al@sub 2@O@sub 3@ by oxygen-plasma-enhanced molecular beam epitaxy has been investigated with reflection high-energy electron diffraction, non-contact atomic force microscopy, X-ray photoelectron spectroscopy, X-ray photoelectron diffraction, low-energy electron diffraction, and high-energy ion scattering. The epilayer is facetted due to compressional stress on the c-plane during growth of the first two monolayers. The epilayer structure is significantly distorted, with considerable in-plane strain. However, the film exhibits a constant Fe 2p binding energy with respect to the O 1s binding energy for all thicknesses, revealing the growth of phase-pure @alpha@-Fe@sub 2@O@sub 3@ throughout. A growth-mode transition begins at approximately two monolayers from strained wetting layer to the formation of clusters of rhombohedral islands when a relatively slow growth rate of 1 Å/min is used. However, this transition occurs over several monolayers at a growth temperature of 400 @super o@C. A film with high structural order and orientational stability grows as the islands coalesce to form new and larger terraces. This transition to island-mediated growth can be kinetically impeded for higher growth rates of 0.1-0.3 Å/sec.@footnote 1@ In contrast, the growth-mode transition will occur more rapidly if temperatures of 450 to 500 @super o@C are used along with the slower growth rate. However, sustained growth at temperatures in excess of 500 @super o@C results in the simultaneous formation of Fe@sub 3@O@sub 4@ (111) and/or @gamma@-Fe@sub 2@O@sub 3@ (111) along with @alpha@-Fe@sub 2@O@sub 3@(0001). In contrast to growth in the c-plane, the epilayer shows only facetted growth on the r-plane, regardless of the deposition rate and substrate temperature. This result may be due to the lower surface symmetry of the r-plane compared to the c-plane. @FootnoteText@ @footnote 1@ S. I. Yi, Y. Liang, S. A. Chambers, to be published in JVST A, Jul/Aug, 1999