Dimensionality in the alloy–de-alloy phase transition of Ag/Cu(1 1 0)

Abstract

The surface morphology and electronic structure of Ag nanostructures on the Cu(1 1 0) surface have been studied with scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). The atomic and electronic dimensionality and the bonding nature of the phases formed upon submonolayer vapor deposition of the Ag are probed. At very low Ag coverages, <0.4 ML, the Ag atoms substitutionally alloy into the Cu surface layer and form a surface-alloy phase. Due to compressive strain along the close-packed direction of the Cu(1 1 0) surface plane, the substituted Ag atoms preferentially align along the [0 0 1] direction. For the Ag d-states, this tendency reveals a two-dimensional-like electronic structure along the [0 0 1] direction and a one-dimensional structure along the [ 1 1 ¯ 0 ] direction due to the weak interaction of the uncoordinated Ag atoms in this direction. At Ag coverages above 0.4 ML, a de-alloy phase transition occurs resulting in the formation of an Ag dimer- and trimer-chain structure with alloyed Ag atoms confined in between the chains. It is shown that, electronically, this phase has a three-dimensional structure. For even higher Ag coverages (0.65 ML), the dimer and trimer chains coalesce and develop into a broader and more ordered striped structure, resulting in one-dimensional electronic behavior of the Ag d-states along to the stripes. However, the strong interaction between the Ag atoms and hybridization of Ag sp and Cu d-states induce two-dimensional electronic structure in the direction perpendicular to the stripes.