Growth of Single-Crystal and Polycrystalline Thin Films of MgAl2O4 and MgFe2O4 |
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Authors: | J J COMER N C TOMBS J F FITZGERALD |
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Affiliation: | Sperry Rand Research Center, Sperry Rand Corporation, Sudbury, Massachusetts 01776 |
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Abstract: | Single-crystal and polycrystalline films of Mg-Al2O4 and MgFe2O4 were formed by two methods on cleavage surfaces of MgO single crystals. In one procedure, aluminum was deposited on MgO by vacuum evaporation. Subsequent heating in air at about 510°C formed a polycrystalline γ-Al2O8 film. Above 540°C, the γ-Al2O, and MgO reacted to form a single-crystal MgAl2O4 film with {001} MgAl2O4‖{001} MgO. Above 590°C, an additional layer of MgAl2O4, which is polycrystalline, formed between the γ-Al2O3 and the single-crystal spinel. Polycrystalline Mg-Al2O4 formed only when diffusion of Mg2+ ions proceeded into the polycrystalline γ-Al2O3 region. Corresponding results were obtained for Mg-Fe2O4. MgAl2O4 films were also formed on cleaved MgO single-crystal substrates by direct evaporation, using an Al2O3 crucible as a source. Very slow deposition rates were used with source temperatures of ~1350°C and substrate temperatures of ~800°C. Departures from single-crystal character in the films may arise through temperature gradients in the substrate. |
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