STACKING OF AG LAYERS ON PT(111)

Ultrathin Ag films grown epitaxially on Pt(111) were studied by photoe lectron forward scattering using synchrotron radiation. The complete a ngular distributions of the Ag 3d electrons at similar to 500 eV kinet ic energy were recorded in a cone with 88 degrees opening angle using a two-dimensional display-type analyzer. The images reveal that the se cond Ag layer grows at room temperature predominantly in a hcp stackin g sequence with respect to the pseudomorphic first Ag layer, After ann ealing to 750 K most of the second layer Ag atoms assume fee sites, Fu rther Ag layers continue to grow in a fee stacking sequence relative t o the first two Ag layers. Annealing does not change the stacking of t hicker films. Thick fee Ag films can be grown in a twin orientation wi th respect to the Pt(111) substrate at room temperature or in the subs trate orientation if the second Ag layer is annealed.