Structural analysis of the intermetallic surface compound CePt sub(5)/Pt(111)

We report on a detailed low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM) study of the intermetallic surface compound CePt sub(5) on Pt(111). Depending on the thickness we observe various diffraction patterns and superstructures. In the low-thickness regime a slightly compressed (2 x 2) superstructure is aligned along the [left angle bracket]110[right angle bracket] direction of the Pt(111) substrate. STM reveals another, much larger superstructure with a periodicity of (9.02 + or - 0.45) nm presumably responsible for the strongly broadened LEED spots. At about 3 unit cells (u.c.) the surface is dominated by a (3[radical]3 x 3[radical]3) R30[degrees] pattern as revealed by LEED satellites and Fourier-transformed high-resolution STM images. It is interpreted as a moire pattern between the film and the substrate. We precisely determine the superstructure of the intermetallic film to ([10/9][radical]3 x [10/9][radical]3) R30[degrees] with respect to the Pt(111) substrate. Above 3 u.c. the satellites progressively disappear. A model is developed that consistently describes this thickness-dependent transition. For CePt sub(5) films with a thickness between 6 and 11 u.c. the lattice of the compressed (2 x 2) superstructure rotates back into the substrate's [left angle bracket]110[right angle bracket] directions.