کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5424856 | 1395839 | 2007 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: The specific oxidation mechanism in the initial stages of O2 adsorption on submonolayer Ba covered W(1 1 0) surface The specific oxidation mechanism in the initial stages of O2 adsorption on submonolayer Ba covered W(1 1 0) surface](/preview/png/5424856.png)
The initial oxidation of a polarized 0.35-ML Ba-covered W(1 1 0) surface has been investigated in detail by high-resolution photoemission spectroscopy using synchrotron radiation. Upon small exposures (⩽0.15 L) to O2, both interfacial W 4f (Ba-coordinated W) and Ba 4d core levels shift simultaneously toward smaller binding energies and then fix during 0.15-0.25 L, finally disappear at 0.6 L. The concurrent negative shifts of both interfacial W 4f and Ba 4d peaks can be attributed to be a consequence of the increased occupancy of 5d states. This explanation is supported by the variations of 5d stats in valence band spectra upon the initial oxidation. Our results clearly demonstrate that charge rearrangement is the dominant effect in the surface reactivity of our oxidized surface. We also found that this charge redistribution is associated with a structural change during oxidation, which is in contrary to previous studies of alkali-metal promotion. That is, oxygen is first chemisorbed atop the polarized Ba adlayer, then incorporates beneath Ba adatoms to form a covalent Ba-O-W complex upon further dosage, and reacts strongly with the Ba overlayer to become an ionic Ba+2Oâ2 surface dipole layer at 0.6 L.
Journal: Surface Science - Volume 601, Issue 7, 1 April 2007, Pages 1726-1735