Atomic structure of a metastable, c(2 x 2) mn surface alloy on Pd(001)

Abstract

We investigate the atomic structure of an ordered Mn surface alloy on Pd(001) by low energy electron diffraction (LEED) I/V (diffraction spot intensity versus beam energy) analysis. A 0.5 monolayer of Mn forms a checkerboard-like c(2 x 2) Mn0.5Pd0.5 alloy confined in the very surface layer (surface-confined alloy) on an almost bulk-like Pd(001) substrate. This structure is contrasted with that of the recently reported subsurface alloy in which the alloyed layer resides 1 ML below the Pd capping layer. First-principles total energy calculations suggest that the surface-confined alloy is unstable with respect to the subsurface alloy. With regard to the previous results on the kinetic behavior of the Mn sublayer, the observed metastable structure of the surface-confined alloy is considered to be a diffusion-limited phase with the Mn sublayer on its way to the subsurface position.