Influence of sputtering on the valence band of Mo, Ni and MoNi3 alloy

The valence band spectra (VBS) of Mo, Ni and MoNi3 alloys were recorded after different surface treatments: (i) after sputtering by 1 keV and 3 keV Ar+ ions, (ii) after annealing at 673 K and (iii) after scraping in situ. In the case of Mo it has been found that contamination of the surface by up to 3 at.% oxygen is responsible for only a small intensity increase on the high energy side, while a carbon concentration of 0.6 at.% plus 3.5 at.% of oxygen smears the fine structure of Mo VBS. After Ar+ ion sputtering and scraping in situ the VBS are almost identical. This indicates that the surface of Mo after Ar+ ion bombardment still has some crystalline order. The photoemission from polycrystalline Mo is determined mainly by the electronic structure of the bulk material and is in good agreement with theoretical predictions. The final-state effect only slightly affected the calculated DOS. This is not valid for the XPVB spectrum of Ni. Sputtering of MoNi3 alloys changes the surface composition and the shape of the valence band. Annealing of the sputtered alloys at 673 K did not restore their initial composition.