THE GROWTH OF SILVER ON A RUTHENIUM (10(1)OVER-BAR 0) SURFACE

摘要

The interaction of Ag with a Ru() surface has been examined between 80 and 500 K using LEED, AES, TPD and chemisorptive titration techniques. Interestingly, we observe a stable Ag-induced c(2 x 2) LEED phase over the large coverage (Theta) range (0.06 less than or equal to Theta less than or equal to 0.65), indicating the formation of two-dimensional ordered Ag islands due to attractive Ag-Ag interactions. As Theta reaches similar to 0.6, further Ag deposition causes parallel first-layer filling and gradual 3D-clustering, accompanied by the successive development of(incomplete)(10 x 1) and c(14 x 5) structures. This latter phase remains stable up to the largest silver coverages studied (similar to Theta approximate to 6 - 8). Titration with CO and/or hydrogen reveals that even for Theta = 5 a few Ru sites remain accessible pointing to a somewhat porous Ag overlayer. In TPD, two binding states appear which we associate with chemisorbed and condensed Ag, respectively, whereby the first state exhibits an increase of the binding energy at medium Theta due to attractive interactions, and the second (multilayer state) corresponds to the sublimation enthalpy of bulk silver. Our combined results indicate a simultaneous multilayer (SM) or a pseudo-Frank-van-der-Merwe growth leading to relatively rough Ag films whose structure is determined by the corrugation of the Ru substrate: true epitactic growth of Ag cannot be observed up to 8 nominal Ag monolayers. References: 65