On growth of epitaxial vanadium oxide thin film on sapphire (0001)
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On growth of epitaxial vanadium oxide thin film on sapphire (0001) Tsung-Han Yanga) Department of Materials Science and Engineering, North Carolina State University, EB-I, Centennial Campus, Raleigh, North Carolina 27695-7907
Chunming Jin Joint Department of Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina 27599
Ravi Aggarwal Department of Materials Science and Engineering, North Carolina State University, EB-I, Centennial Campus, Raleigh, North Carolina 27695-7907
R.J. Narayan Joint Department of Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina 27599
Jay Narayan Department of Materials Science and Engineering, North Carolina State University, EB-I, Centennial Campus, Raleigh, North Carolina 27695-7907 (Received 5 June 2009; accepted 26 August 2009)
We report the characteristics of epitaxial growth and properties of vanadium oxide (VO2) thin films on sapphire (0001) substrates. Pulsed laser deposition was used to grow (002) oriented VO2 films on sapphire (0001). Transmission electron microscopy studies showed that the orientation relationship between the substrate and the thin film is: (002)f2k(0006)sub3 and [010]f2 k½21 10sub. It was also established that VO2 has three different orientations in the film plane which are rotated by 60 from each other. The epitaxial growth of vanadium oxide on sapphire (0001) has been explained in the framework of domain matching epitaxy (DME). Electrical resistivity measurements as a function of temperature showed a sharp transition with a hysteresis width 5 C, and large resistance change (1.5 104) from the semiconductor phase to the metal phase. It is interesting to note that in spite of large angle twin boundaries in these VO2 films, the SMT characteristics are better than those observed for polycrystalline films. The higher width of thermal hysteresis for the VO2 film on c-sapphire compared to a bulk single VO2 crystal and a single-crystal VO2 film on r-sapphire can be attributed to the existence of these large-angle twin grain boundaries. These findings can provide insight into the phase transformation characteristics of VO2, which has important applications in switching and memory devices. Vanadium dioxide (VO2) is an attractive material for memory and optical switching applications due to its unique characteristic semiconductor to metal transition (SMT). Vanadium dioxide has a tetragonal structure at temperatures higher than 340 K, and it shows metallic electrical behavior. At temperatures below 340 K, the tetragonal vanadium dioxide transforms into a semiconducting monoclinic phase. This phase transformation is accompanied by a sharp change in electrical conductivity a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0059
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 3, Mar 2010 Downloaded: 16 Mar 2015
and optical reflectivity in the infrared region.1–3 The tetragonal to monoclinic phase transition in VO2 is a first-order phase transi
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