Epitaxial Growth and Properties of MBE Grown Ferromagnetic Co-doped TiO₂ Anatase Films on SrTiO₃(001) and LaAlO₃(001)

Journal Article · Tue Oct 15 04:00:00 EDT 2002 · Thin Solid Films, 418(2):197-210

DOI:https://doi.org/10.1016/S0040-6090(02)00709-5· OSTI ID:15006939

Chambers, Scott A.; Wang, Chong M.; Thevuthasan, Suntharampillai; Droubay, Timothy C.; McCready, David E.; Lea, Alan S.; Shutthanandan, V.; Windisch, Charles F.

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/sec) is used over a substrate temperature range of 550 degrees Celcius to 600 degrees celcius. 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/sec) 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. Co appears to substitute for Ti in the lattice and exhibits a ⁺² formal oxidation state. Both pure and Co-doped films are typically n-type semiconductors despite the lack of intentional n-type doping, although a wide range of conductivities is observed.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15006939
• Report Number(s): PNNL-SA-35981
• Journal Information: Thin Solid Films, 418(2):197-210, Journal Name: Thin Solid Films, 418(2):197-210
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
OPA-MBE
anatase
rutile
single-crystal films
thin films