Berlin 2005 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

O: Oberflächenphysik

O 27: Phasenüberg
änge

O 27.3: Talk

Saturday, March 5, 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.