Dresden 2011 – scientific programme
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O: Fachverband Oberflächenphysik
O 14: Clean surfaces: Metals, semiconductors, oxides and insulators I
O 14.7: Talk
Monday, March 14, 2011, 16:30–16:45, WIL B122
Epitaxial films of praseodymia on Si(111): controlled modification from Pr2O3 to PrO2 via plasma and thermal treatment — •Sarah Röhe1, Andreas Schaefer1, Volkmar Zielasek1, Thomas Schroeder2, and Marcus Bäumer1 — 1IAPC, Universität Bremen — 2IHP, Frankfurt (Oder)
A cold RF oxygen plasma treatment is demonstrated as a successful route to prepare clean, well-ordered and stoichiometric PrO2 layers on silicon which are very difficult to obtain by other techniques. As a starting point, cubic PrO2−Δ films are obtained by growing hexagonal Pr2O3 on Si(111) by MBE and annealing these layers to 720 K in oxygen atmosphere. The subsequent plasma treatment is performed in a plasma cell directly attached to a UHV chamber so that samples can be transferred to XPS without breaking vacuum. The Pr 3d XP spectra show so far unobserved spectral characteristics presenting a fingerprint for PrO2. The XPS data provide insight into the special role of praseodymia among the rare earth oxides. They also reveal that former XP studies of praseodymia suffered from significant reduction at the surface. Starting with PrO2 films prepared by oxygen plasma, different oxidation states of praseodymia can be obtained by reducing the oxide in a controlled way via thermal treatment. Several temperature-programmed desorption peaks of O2 are observed in the range from 300 to 900 K and indicate phase transitions. The different praseodymia phases are studied with respect to their activity towards CO oxidation at their surface under UHV conditions.