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 st ages of thin epitaxial Al films on Ru(0001) by work function measureme nts and scanning tunnelling microscopy. A characteristic break in the work function versus coverage relation, at 0.15 monolayers, can be rel ated to a structural change in the growing film. After 3.5 layer depos ition the work function saturates at the value of clean Al(111). Annea ling leads to surface alloying, which is accompanied by a dramatic inc rease of the work function. The work function changes during oxygen up take resemble those obtained on bulk Al(111); the stronger absolute de crease and the shift of characteristic break points to lower exposure indicate an earlier onset of oxidation, consistent with the higher def ect density on the film as compared to bulk Al surfaces.