Co-doped Anatase TiO₂ Heteroepitaxy on Si(001)

Journal Article · Fri Apr 01 04:00:00 EST 2005 · Journal of Applied Physics, 97(7):073511-073511-10

DOI:https://doi.org/10.1063/1.1868854· OSTI ID:15016049

Kaspar, Tiffany C.; Droubay, Timothy C.; Wang, Chong M.; Heald, Steve M.; Lea, Alan S.; Chambers, Scott A.

Pure anatase TiO₂ and CoxTi₁-x O₂ (0.01 < x < 0.04) epitaxial thin films were deposited by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) on Si(001) for evaluation as a potential dilute magnetic semiconductor material suitable for Si-based spintronic devices. Epitaxial growth on Si(001) was facilitated by the deposition of ¼or ½ ML Sr metal on the clean Si(001) surface to form an oxidation resistant silicide layer, followed by deposition of a thin SrTiO₃ buffer layer. Using ½ ML Sr metal to form the silicide allowed the deposition of 10 ML SrTiO₃ without oxidation of the Si interface. Epitaxial anatase could be grown on this heterostructure, although use of the oxygen plasma during deposition resulted in significant SiO₂ formation. Pure anatase films consisted of epitaxial anatase surface particles on a continuous anatase film. For Co-doped films, Co segregation to surface particles of epitaxial anatase was observed by Auger electron spectroscopy and transmission electron microscopy (TEM); faceting of the particles was observed for low Co doping concentrations. Although no secondary phases containing Co were observed in Co-doped anatase films by x-ray diffraction or TEM, x-ray absorption near edge spectroscopy indicated Co was present in the films as a mixture of Co(0), Co(II), and Co(III). All samples were ferromagnetic at room temperature; for lower Co concentrations, the ferromagnetic remanence (9%) and coercive field (100 Oe) were similar to phase-pure Co:TiO₂ / LaAlO₃. However, the presence of Co(0) under strongly oxidizing growth conditions known to oxidize the Si interface implies that under no deposition conditions can Co metal be eliminated while simultaneously protecting the Si interface from oxidation.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15016049
• Report Number(s): PNNL-SA-42653; 6292; KC0203020
• Journal Information: Journal of Applied Physics, 97(7):073511-073511-10, Journal Name: Journal of Applied Physics, 97(7):073511-073511-10 Journal Issue: 7 Vol. 97; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION
AUGER ELECTRON SPECTROSCOPY
BUFFERS
DEPOSITION
Environmental Molecular Sciences Laboratory
MAGNETIC SEMICONDUCTORS
MIXTURES
MOLECULAR BEAM EPITAXY
OXIDATION
OXYGEN
SEGREGATION
SILICIDES
SPECTROSCOPY
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION