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O: Oberflächenphysik
O 27: Phasenüberg
änge
O 27.3: Vortrag
Samstag, 5. März 2005, 15:30–15:45, TU EB107
Metal-to-semiconductor phase transitions in VO2 films — •Helena Prima Garcia1, Tatjana Gießel1, Emily Hooker2, Martin Polcik2, and Wolf Widdra3 — 1Max-Born-Institute, Berlin, Germany — 2Fritz-Haber-Institute der Max-Planck-Gesellschaft, Berlin, Germany — 3Martin Luther University, Halle, Germany
VO2 films were grown by subsequent vanadium deposition and oxidation on TiO2(110) with film thickness’ ranging from less than one monolayer to approximately 100 nm and additionally thicker VO2 films (thickness 200 nm) grown by reactive RF sputtering.
While ultrathin films up to a few monolayers grow nearly epitaxially preserving the structure of the substrate, thicker films grown by subsequent vanadium deposition and oxidation show a polycrystalline structure with a preferential azimuthal orientation of the high symmetry directions in the crystallites parallel to the high symmetry directions of the TiO2(110) surface. All thermally grown films show only subtle changes in the V 3d region of the valence band as a function of temperature at which VO2 undergoes a metal-to-semiconductor phase transitions (MSPT at 340 K).
In contrast the thicker VO2 films grown by reactive RF sputtering show a substantial change in the region of the V 3d level. The spectral analysis of the change at V 3d region reveals the transition temperature around 310K and the width of the hysteresis loop of ∼ 15 K. The relatively broad transition range of ∼ 71 K could be explained by the different size of the VO2 particles as observed by AFM.