Structural and spectroscopic investigation of the Yb/Al(001) interface in the submonolayer coverage range

The formation of submonolayer Yb overlayers on Al(001) has been studied by angle-scanned full-hemispherical X-ray photoelectron diffraction and angle-resolved ultraviolet photoelectron spectroscopy. It is shown that different phases, as observed by low-energy electron-diffraction, are formed up to a coverage of 0.5 ML where the first Yb layer is completed. An intimate connection of spectroscopic and structural properties is observed, reflected by marked changes of the Yb 4f core level spectra with increasing coverage. The surface Yb atoms are found to remain in the divalent 4f(14) state for the full coverage range. Upon formation of YbAl3-like nuclei at coverages above 0.5 ML, mixed valence of incorporated subsurface Yb atoms is observed, whereas the surface atoms persist in the divalent state. (C) 1997 Elsevier Science B.V.