Abstract
We have investigated the heteroepitaxial growth and materials properties of pure and Co-doped TiO2 anatase on SrTiO3(001) and LaAlO3(001), grown by oxygen plasma assisted molecular beam epitaxy. This material is a promising new diluted magnetic semiconductor that shows large magnetization and a Curie temperature well above room temperature. We have found that epitaxial films with the highest crystalline quality and most uniform distribution of Co result when a rather slow growth rate (∼0.01 nm/s) is used over a substrate temperature range of 550-600 °C on LaAlO3(001). These conditions result in layer-by-layer growth of single-crystal films and a very low density of extremely small nanocrystalline inclusions. In contrast, growth at a higher rate (∼0.04 nm/s) leads to extensive formation of secondary-phase rutile nanocrystals to which Co diffuses and segregates. The rutile nanocrystals nucleate on the evolving anatase film surface in such a way that lattice strain between the two phases is minimized. Cobalt appears to substitute for Ti in the lattice and exhibits a +2 formal oxidation state. Both pure and Co-doped films can be grown as n-type semiconductors by controlled incorporation of oxygen atom vacancies. Free electrons are required to couple the Co(II) spin to a ferromagnetic state.
| Original language | English |
|---|---|
| Pages (from-to) | 197-210 |
| Number of pages | 14 |
| Journal | Thin Solid Films |
| Volume | 418 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 15 Oct 2002 |
| Externally published | Yes |
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Keywords
- Magnetic properties and measurements
- Molecular beam epitaxy (MBE)
- Semiconductors
- Titanium oxide
ASJC Scopus subject areas
- Surfaces, Coatings and Films
- Condensed Matter Physics
- Surfaces and Interfaces
Cite this
Epitaxial growth and properties of MBE-grown ferromagnetic Co-doped TiO2 anatase films on SrTiO3(001) and LaAlO3(001). / Chambers, S. A.; Wang, C. M.; Thevuthasan, S.; Droubay, T.; McCready, D. E.; Lea, A. S.; Shutthanandan, V.; Windisch, Jr F.
In: Thin Solid Films, Vol. 418, No. 2, 15.10.2002, p. 197-210.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Epitaxial growth and properties of MBE-grown ferromagnetic Co-doped TiO2 anatase films on SrTiO3(001) and LaAlO3(001)
AU - Chambers, S. A.
AU - Wang, C. M.
AU - Thevuthasan, S.
AU - Droubay, T.
AU - McCready, D. E.
AU - Lea, A. S.
AU - Shutthanandan, V.
AU - Windisch, Jr F.
PY - 2002/10/15
Y1 - 2002/10/15
N2 - We have investigated the heteroepitaxial growth and materials properties of pure and Co-doped TiO2 anatase on SrTiO3(001) and LaAlO3(001), grown by oxygen plasma assisted molecular beam epitaxy. This material is a promising new diluted magnetic semiconductor that shows large magnetization and a Curie temperature well above room temperature. We have found that epitaxial films with the highest crystalline quality and most uniform distribution of Co result when a rather slow growth rate (∼0.01 nm/s) is used over a substrate temperature range of 550-600 °C on LaAlO3(001). These conditions result in layer-by-layer growth of single-crystal films and a very low density of extremely small nanocrystalline inclusions. In contrast, growth at a higher rate (∼0.04 nm/s) leads to extensive formation of secondary-phase rutile nanocrystals to which Co diffuses and segregates. The rutile nanocrystals nucleate on the evolving anatase film surface in such a way that lattice strain between the two phases is minimized. Cobalt appears to substitute for Ti in the lattice and exhibits a +2 formal oxidation state. Both pure and Co-doped films can be grown as n-type semiconductors by controlled incorporation of oxygen atom vacancies. Free electrons are required to couple the Co(II) spin to a ferromagnetic state.
AB - We have investigated the heteroepitaxial growth and materials properties of pure and Co-doped TiO2 anatase on SrTiO3(001) and LaAlO3(001), grown by oxygen plasma assisted molecular beam epitaxy. This material is a promising new diluted magnetic semiconductor that shows large magnetization and a Curie temperature well above room temperature. We have found that epitaxial films with the highest crystalline quality and most uniform distribution of Co result when a rather slow growth rate (∼0.01 nm/s) is used over a substrate temperature range of 550-600 °C on LaAlO3(001). These conditions result in layer-by-layer growth of single-crystal films and a very low density of extremely small nanocrystalline inclusions. In contrast, growth at a higher rate (∼0.04 nm/s) leads to extensive formation of secondary-phase rutile nanocrystals to which Co diffuses and segregates. The rutile nanocrystals nucleate on the evolving anatase film surface in such a way that lattice strain between the two phases is minimized. Cobalt appears to substitute for Ti in the lattice and exhibits a +2 formal oxidation state. Both pure and Co-doped films can be grown as n-type semiconductors by controlled incorporation of oxygen atom vacancies. Free electrons are required to couple the Co(II) spin to a ferromagnetic state.
KW - Magnetic properties and measurements
KW - Molecular beam epitaxy (MBE)
KW - Semiconductors
KW - Titanium oxide
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U2 - 10.1016/S0040-6090(02)00709-5
DO - 10.1016/S0040-6090(02)00709-5
M3 - Article
VL - 418
SP - 197
EP - 210
JO - Thin Solid Films
JF - Thin Solid Films
SN - 0040-6090
IS - 2
ER -