Combined work function and STM study on growth, alloying and oxidation of epitaxial aluminum films on Ru(0001)

We have investigated growth, thermal alloying and initial oxidation stages of thin epitaxial Al films on Ru(0001) by work function measurements and scanning tunnelling microscopy. A characteristic break in the work function versus coverage relation, at 0.15 monolayers, can be related to a structural change in the growing film. After 3.5 layer deposition the work function saturates at the value of clean Al(111). Annealing leads to surface alloying, which is accompanied by a dramatic increase of the work function. The work function changes during oxygen uptake resemble those obtained on bulk Al(111); the stronger absolute decrease and the shift of characteristic break points to lower exposure indicate an earlier onset of oxidation, consistent with the higher defect density on the film as compared to bulk Al surfaces.