Growth of Ce on Rh(1 1 1)

We have studied the growth of cerium films on Rh(1 1 1) using STM (scanning tunneling microscopy), LEED (low energy electron diffraction), XPS (X-ray photoelectron spectroscopy) and AES (Auger electron spectroscopy). Measurements of the Ce films after room temperature deposition showed that Ce is initially forming nanoclusters in the low coverage regime. These clusters consist of 12 Ce atoms and have the shape of pinwheels. At a coverage of 0.25 ML (monolayer, ML) an adatom layer with a (2 × 2) superstructure is observed. Above 0.4 ML, Rh is diffusing through pinholes into the film, forming an unstructured mixed layer. Annealing at 250 °C leads to the formation of ordered Ce-Rh compounds based on the bulk compound CeRh₃. At a coverage of 0.1 ML, small ordered (2 × 2) surface alloy domains are observed. The exchanged Rh atoms form additional alloy islands situated on the pure Rh(1 1 1) surface, showing the same (2 × 2) superstructure as the surface alloy. At a coverage of 0.25 ML, the surface is completely covered by the surface alloy and alloy islands. The (2 × 2) structure is equivalent to a (1 1 1)-plane of CeRh₃, contracted by 6%. Annealing a 1 ML thick Ce layer leads to a flat surface consisting of different rotational domains of CeRh₃(1 0 0). The Rh needed for alloy formation comes from 50 Å deep pits in the substrate. Finally we show that LEIS (low energy ion scattering) is not suitable for the characterization of Ce and CeRh films due to strong effects of neutralization.