Structural analysis of the intermetallic surface compoundCePt5/Pt(111)

Abstract

We report on a detailed low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM) study of the intermetallic surface compound ${\mathrm{CePt}}_{5}$ on Pt(111). Depending on the thickness we observe various diffraction patterns and superstructures. In the low-thickness regime a slightly compressed $(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure is aligned along the $\ensuremath{\langle}1\overline{1}0\ensuremath{\rangle}$ direction of the Pt(111) substrate. STM reveals another, much larger superstructure with a periodicity of ($9.02\ifmmode\pm\else\textpm\fi{}0.45$) nm presumably responsible for the strongly broadened LEED spots. At about 3 unit cells (u.c.) the surface is dominated by a $(3\sqrt{3}\ifmmode\times\else\texttimes\fi{}3\sqrt{3})R{30}^{\ensuremath{\circ}}$ pattern as revealed by LEED satellites and Fourier-transformed high-resolution STM images. It is interpreted as a moir\'e pattern between the film and the substrate. We precisely determine the superstructure of the intermetallic film to $(\frac{10}{9}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\frac{10}{9}\sqrt{3})R{30}^{\ensuremath{\circ}}$ 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 ${\mathrm{CePt}}_{5}$ films with a thickness between 6 and 11 u.c. the lattice of the compressed $(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure rotates back into the substrate's $\ensuremath{\langle}1\overline{1}0\ensuremath{\rangle}$ directions.