The versatile catalytic activity of palladium in combination with the tendency of its (110) surface towards restructuring upon gas or alkali adsorption intrigues researchers to investigate and understand the interaction of gasses with this surface for many decades now. Particularly interesting are the oxygen adsorption phenomena and a new burst came with the application of density functional theory (DFT) where many adsorption phases were revisited with the focus on atomic details.
The complexity of the oxygen-Pd(110) system manifests itself in a number of observed phases which depend on oxygen coverage. According to the plain low energy electron diffraction (LEED) measurements [1-4] the following patterns have been reported: (1x3), (1x2), c(2x6), c(2x4), (2x3)-1D, and a "complex" pattern. The adsorption structures were related to submonolayer oxygen coverages and the earliest studies were suggesting models in which the palladium (110) surface does not reconstruct [1-3]. As the complexity of systems was better understood and combinations of more structure-sensitive measurements were conducted, the resulting descriptions included also models of a reconstructed surface [4,5].
As to the mentioned observed O/Pd(110) structures the mojority of data has been published in relation to the c(2x4) LEED pattern, which is easy to reproduce in the experiment, obviously indicating that the c(2x4) structure represents the most stable oxygen induced surface phase. In this work we explored the O/Pd(110) phase diagram in greater extent where we applied DFT calculations to precisely understand the atomistic arrangements of possible surface oxide structures. In the experiment we have focused on very low oxygen coverages resulting in globally less stable surface oxide phases which were then characterized with atomically resolving scanning tunneling microscopy (STM). In particular, we have characterized the (3x2) phase and find that the measured data are in very good agreement with the theoretical predictions.
[1] Ertl, Rau, Surf. Sci. 15 (1969) 443.
[2] Nishijima, et al., Solid State Commun. 60 (1986) 257.
[3] Jo, et al., Chem. Phys. Lett. 131 (1986) 106.
[4] Goschnick, et al., Surf. Sci. 178 (1986) 831.
[5] He, et al., J. Chem. Phys. 90 (1989) 5082. |