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H. Li, J. Choi, W. Mayr-Schmölzer, C Weilach, Ch. Rameshan, F. Mittendorfer, J. Redinger, M. Schmid, G. Rupprechter:
"The growth of an ultrathin zirconia film on Pt3Zr examined by-HR-XPS, TPD, STM and DFT";
Journal of Physical Chemistry C, 119 (2015), 2462 - 2470.

ABSTRACT: Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline
Pt3Zr(0001) substrate by oxidation in 1 × 10−7 mbar of O2 at 673 K, followed by annealing
at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for
reforming catalysts and fuel cell anodes. The atomic and electronic structure and
composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray
photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron
diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory
(DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O−Zr−O) films on the
alloy; only a small area fraction (10−15%) is covered by ZrO2 clusters (thickness ∼0.5−10
nm). The amount of clusters decreases with increasing annealing temperature. Temperatureprogrammed
desorption (TPD) of CO was utilized to confirm complete coverage of the
Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and
DFT calculations show that the core level shifts of Zr in the trilayer ZrO2
films are between
those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core
level shifts to substoichiometric ZrOx is not necessarily correct, because these XPS signals may equally well arise from ultrathin
ZrO2
films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts
by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.

http://dx.doi.org/10.1021/jp5100846