Thermal stability of the Ta(1 1 1) surface covered with chemisorbed metal layer. Part I: Au

When the Ta(1 1 1) surface is covered with at least one pseudomorphic layer of Au, after annealing to 700 K the pyramids are created. Their base is a regular triangle of side length 14 Å corresponding to a threefold lattice constant of the substrate. Thermal instability of the substrate is observed when the surface is covered with less than three layer of Au. Heating at T<1100 K leads to the formation of an elevations which are a form of adsorbate agglomeration. Inclination of the steep sides equals to 11° with respect to the substrate surface. No faceting occurs, like that observed for the W(1 1 1) surface. The transition of the pseudomorphic layer into the close packed Au(1 1 1) layer at θ>1.5 ML caused by the concentration change occurs, as well as the reverse transition at θ>2.6 ML.