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Condensed Matter Seminars

ics Condensed Matter
Thursday, April 19, 2012
3:30 PM
Physics Building, Room 204
Note special time.
Note special room.
Salinporn Kittiwatanakul [Host: Stu Wolf]
University of Virginia
"Transport Properties of VO2 Films near the Metal-Semiconductor Transition"
Vanadium dioxide (VO2) exhibits a metal semiconductor transition (MST) at 340 K. This transition is accompanied by the abrupt change in the electrical conductivity, optical transmittance and reflectance in infrared region, which can be used in the electronic devices such as temperature sensors and electric switches. In this study, Reactive Bias Target Ion Beam Deposition was used for epitaxial VO2 growth on TiO2 (100) substrates with fixed O2 flow rate at 5.0 sccm to study transport anisotropy, and for highly textured VO2 growth on c-plane Al2O3 substrates to study the effect of different O2 flow rates (4.5-6.0 sccm). The conductivity anisotropy ratio σc/σb of VO2/TiO2 film was found to be ~41.5 at 300 K, much larger than that of single crystal VO2 and it is the largest among those previously reported. The temperature dependent anisotropy of the carrier concentration and the mobility is to be discussed. With XPS and XAS, the valence state of vanadium on different VO2/c-Al2O3 films was investigated. As the O2 flow rate increases, the XRD results show decreasing lattice parameter, hence increasing compressive strain along b-axis of monoclinic VO2; the transport measurements also show the increasing transition temperature (TMST) and the increasing change in resistivity associated with the strain. The correlation among the valence state, the strain and MST in VO2 will be discussed.

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