"Stability of Pt-Modified Cu(111) in the Presence of Oxygen and Its Implication on the Overall Electronic Structure"

Henrik Öberg: Toyli Anniyev, Aleksandra Vojvodic, Sarp Kaya, Hirohito Ogasawara, Daniel Friebel, Daniel J. Miller, Dennis Nordlund, Uwe Bergmann, Mathias P. Ljungberg, Frank Abild-Pedersen, Anders Nilsson, and Lars G. M. Pettersson; The Journal of Physical Chemistry, 07/18/13.

Additional Authors: Toyli Anniyev, Aleksandra Vojvodic, Sarp Kaya, Hirohito Ogasawara, Daniel Friebel, Daniel J. Miller, Dennis Nordlund, Uwe Bergmann, Mathias P. Ljungberg, Frank Abild-Pedersen, Anders Nilsson, and Lars G. M. Pettersson

Abstract:

The electronic structure and stability of Cu(111)-hosted Pt overlayers with and without the presence of atomic oxygen have been studied by means of core-level spectroscopy and density functional theory (DFT). Because of lattice mismatch, Pt(111) overlayers grown on Cu(111) are compressively strained, and hard X-ray photoelectron spectroscopy together with Pt L3-edge X-ray absorption spectroscopy (XAS) reveals a pronounced downshift of the Pt d-band owing to the increased overlap of the d-orbitals, an effect also reproduced theoretically. Exposure to oxygen severely alters the surface composition; the O–Cu binding energy largely exceeds that of O–Pt, and DFT calculations predict surface segregation of Cu atoms. Comparing the adsorbate electronic structure for O on unstrained Pt(111) with that of O on Pt-modified Cu(111) using O K-edge XAS and X-ray emission spectroscopy salient differences are observed and calculations show that Cu-segregation to the topmost layer is required to reproduce the measured spectra. It is proposed that O is binding in a hollow site constituted by at least two Cu atoms and that up to 75% of the Pt atoms migrate below the surface.