BA DEPOSITION ON NI(110)

The deposition of Ba on Ni(110) at room temperature was studied by AES , TDS, LEED, as well as SEECC and work function measurements. Ba was f ound to form a first layer consisting of a mixture of random c(2 X 2) domains and disordered adatoms. The first break in the AES uptake curv e is estimated to be similar to 3/4 ML. A second, more weakly bound di sordered layer follows. Heating to similar to 200 degrees C turns simi lar to 0.35 ML to a subsurface phase which is stable up to 800 degrees C. The system becomes mobile at similar to 500 degrees C opening up t wo kinetic channels: (a) desorption of some of the second layer atoms at similar to 500 degrees C, (b) conversion of the rest of these atoms to long-range c(2 X 2). Finally, desorption from the c(2 X 2) phase o ccurs at similar to 780 degrees C. The binding energy of the first lay er atoms is similar to 2.9 eV at all coverages contrary to alkali meta ls deposition where it decreases with coverage, whereas the initial di pole moment is similar to 13 D, i.e. similar to the alkali metals.