Surface oxides on Pd(111): STM and density functional calculations

Author(s): J Klikovits, E Napetschnig, Michael A. Schmid, Nicola Seriani, Orest Dubay, Georg Kresse, Peter Varga
Abstract: The formation of one-layer surface oxides on Pd(111) has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). Besides the Pd5 O4 structure determined previously, structural details of six different surface oxides on Pd(111) will be presented. These oxides are observed for preparation in oxygen-rich conditions, approaching the thermodynamic stability limit of the PdO bulk oxide at an oxygen chemical potential of -0.95 to -1.02 eV (570-605 K, 5× 10-4 mbar O2). Sorted by increasing oxygen fraction in the primitive unit cell, the stoichiometry of the surface oxides is Pd5 O4, Pd9 O8, Pd20 O18, Pd23 O21, Pd19 O18, Pd8 O8, and Pd32 O32. All structures are one-layer oxides, in which oxygen atoms form a rectangular lattice, and all structures follow the same rules of favorable alignment of the oxide layer on the Pd(111) substrate. DFT calculations were used to simulate STM images as well as to determine the stability of the surface oxide structures. Simulated and measured STM images are in excellent agreement, indicating that the structural models are correct. Since the newly found surface oxides are clearly less stable than Pd5 O4, we conclude that Pd5 O4 is the only thermodynamically stable phase, whereas all newly found structures are only kinetically stabilized. We also discuss possible mechanisms for the formation of these oxide structures. © 2007 The American Physical Society.
Organisation(s): Computational Materials Physics
External organisation(s): Technische Universität Wien
Journal: Physical Review B
Volume: 76
No. of pages: 9
ISSN: 1098-0121
DOI: https://doi.org/10.1103/PhysRevB.76.045405
Publication date: 2007
Peer reviewed: Yes
Austrian Fields of Science 2012: 1030 Physics, Astronomy
Portal url: https://ucrisportal.univie.ac.at/en/publications/a38cf1b1-f032-48aa-bc0c-bf4fc7a19564