Oxygen on Rare Earth Metal Surfaces

First it will be reported on the investigation of oxygen adsorbed on rare earth metal surfaces using tunable VUV photoelectron spectroscopy [40] followed by the description of scanning tunneling microscopy experiments [3] which were used to determine the very first steps of the adsorption process. 

The underlying background of secondary electrons exhibits no CDAD. These electrons have been inelastically scattered several times and lost their prior angular distribution. Not only the oxygen feature but also the rare earth metal valence bands show different photoelectron intensities indicating that CDAD effects do also arise for thin films and bulk material, respectively. 

In order to extract quantitative information from the photoelectron spectra, an asymmetry function is defined as follows 

The system 0/Gd/W(l 10) exhibits a significantly different behavior for angles smaller than 20°. A pronounced feature overlaps the general shape of the asymmetry curve an additional change of sign and a high maximum of 15% at = —10° (deep minimum of —18% at 10°, respectively) occurs. This observation directly points to different chemical or electronic properties in the adsorbate overlayer. 

For an aligned p valence level of a free atom, the general shape of /cdad should follow sin20 as shown for comparison in Fig. 4.30 [41]. The asymmetry contains 

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