Growth of metastable fcc Co on Ni(001)

Abstract

We have used high-energy Auger-electron diffraction and associated kinematical scattering calculations to determine that Co, which is hcp at room temperature and atmospheric pressure, can be grown as a stable, unstrained fcc film on Ni(001). Studies of the early stages of growth show that the first monolayer equivalent does not cover the surface uniformly but rather forms two-dimensional patches with limited amounts of a second layer. The second monolayer equivalent adds to the second layer of each patch and provides a limited number of third-layer atoms. When the total Co coverage exceeds two monolayer equivalents, the overlayer coalesces into a continuous fcc film with no detectable strain up to 30 monolayers (the highest coverage studied). For comparison, we have measured angular distributions for Cu/Ni(001) with 0.5 and 1.0 monolayer of Cu. From surface thermodynamic considerations, Cu is expected to wet the surface uniformly. However, Cu also tends to form two-layer-deep patches at a coverage of one monolayer equivalent. These results demonstrate that limited surface mobility is significant in determining the morphology of monolayer metal films, in agreement with theoretical models of overlayer growth behavior.