Preparation of (111)-Oriented Epitaxial Fe3−xO4 Films on α-Al2O3 (0001) Substrates by Coating-Pyrolysis Process Using Postepitaxial Topotaxy via (0001)-Oriented α-Fe2O3
✍ Scribed by Iwao Yamaguchi; Tsuyoshi Terayama; Takaaki Manabe; Tetsuo Tsuchiya; Mitsugu Sohma; Toshiya Kumagai; Susumu Mizuta
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 593 KB
- Volume
- 163
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
We have succeeded in preparing the (111)-oriented epitaxial 5lms of magnetite (Fe 3 O 4 ) and maghemite ( -Fe 2 O 3 ), or Fe 3؊x O 4 , on the C-planes of sapphire [ -Al 2 O 3 (0001)] by a coating-pyrolysis (CP) process using postepitaxial topotaxy (PET). In this set of 5lm and substrate, not only the structure type is di4erent, i.e., the cubic spinel type versus hexagonal corundum type, but the lattice mismatch is large, i.e., 8.0%. The PET process consists of one epitaxial growth and one or more topotactic reaction steps. In the present work, a (0001)-oriented epitaxial 5lm of hematite ( -Fe 2 O 3 ) [corundum-type iron (III) oxide] was 5rst formed on an -Al 2 O 3 (0001) substrate by CP process. Second, -Fe 2 O 3 was reduced to Fe 3 O 4 in a gas 6ow of an argon+hydrogen gas mixture with a hydrogen partial pressure of 0.023 atm. Finally, the Fe 3 O 4 was oxidized in air to -Fe 2 O 3 , or Fe 3؊x O 4 . Pole-5gure analysis exhibited that both the products, Fe 3 O 4 and -Fe 2 O 3 , were (111)-oriented and epitaxially grown on the substrate surface. The crystallographic relationship is Fe 3 O 4 , -Fe 2 O 3 (111) "" -Al 2 O 3 (0001) and Fe 3 O 4 , -Fe 2 O 3 [11 0]"" -Al 2 O 3 111 002, 11 1002. This implies that -Fe 2 O 3 (0001) has been topotactically converted to Fe 3 O 4 (111) and -Fe 2 O 3 (111). Magnetic properties and surface morphology of the 5lms were also investigated using SQUID and atomic force microscopy, respectively.