Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 14: Clean surfaces: Metals, semiconductors, oxides and insulators I

O 14.7: Vortrag

Montag, 14. März 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 PrO_2−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.