Growth of Rh, Pd, and Pt films on Cu(100).

The growth of vapor-deposited films of Rh, Pd, and Pt on Cu(100) at 300 K was followed by Auger-electron and low-energy ion scattering spectroscopies. A tendency (strong for Rh, weaker for both Pd and Pt) for Cu to remain on the surface as the film grows was observed, consistent with expectations based on surface energy considerations. The much smaller difference in behavior between Pt and Pd than between Pt and Rh can be related to the heat of mixing, the sign of which is positive for Cu-Rh but negative for both Cu-Pd and Cu-Pt. While agglomeration does not appear to be significant, the experimental results suggest that a fraction of the deposited metal forms clusters, islands, or other configurations which are relatively stable against the surface diffusional processes thought to be responsible for incorporation of adatoms into the bulk. The ordered 50-50 surface alloy phase previously found for Pd on Cu(100) was not observed in the case of Pt, although a c(2×2) low-energy electron-diffraction pattern is produced by the nearly pure Cu surface which results from heating a monolayer (deposited) of either metal to 450 K. Photoemission and chemisorption results reveal other differences among the three combinations of metals.