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Low-temperature processing and control of structure and properties of TiO2/c-sapphire epitaxial heterostructures

Published online by Cambridge University Press:  24 April 2013

Mohammad Reza Bayati*
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907
Shivani Joshi
Affiliation:
Amity Institute of Nanotechnology, Noida, Uttar Pradesh-201301, India
Roger Jay Narayan
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907; and Joint Department of Biomedical Engineering, UNC Chapel Hill and North Carolina State University, Raleigh, North Carolina 27695-7115
Jay Narayan
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907
*
a)Address all correspondence to this author. e-mail: [email protected]
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Abstract

We have investigated the formation of the rutile and the anatase polymorphs of TiO2, with emphasis on epitaxial growth characteristics, and defect content as a function of laser and substrate variables. X-ray diffraction (XRD) studies revealed that the rutile phase is more stable at higher substrate temperatures and lower oxygen pressures; in contrast, decreasing the temperature and increasing the oxygen pressure gave rise to formation of anatase. Epitaxial rutile films with a <100] orientation were obtained at 450 °C using the pressure of 5 × 10−4 Torr, and laser energy of 3.5–4.0 J/cm2. The epitaxial relationship, determined by 2θ−θ and φ scan of XRD and confirmed by transmission electron microscopy (TEM) diffraction patterns, was shown to be rutile(100)||sapphire(0001), rutile[001]||sapphire[10$\bar 1$0] and rutile[010]||sapphire[1$\bar 2$10]. An atomically sharp interface between the rutile epitaxial film and the sapphire substrate was observed in the scanning transmission electron microscopy (STEM) images. The films exhibited a transmittance of 75–90% over the visible region. The absorption edge was observed to shift toward longer wave lengths at higher deposition temperatures or lower pressures. X-ray photoelectron spectroscopy and photoluminescence results showed that concentration of lattice point defects, namely oxygen vacancies and titanium interstitials, increased at lower oxygen pressures. Formation of nanostructured films with a surface roughness of -1.5–13.1 nm was confirmed by atomic force microscopy investigations.

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Copyright © Materials Research Society 2013 

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References

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