Alloy formation of Y with Pd investigated by photoemission and electron diffraction

The structure of Pd capped Y films for an application as a switchable mirro r was studied. The surface structures are investigated by reflecting high e nergy electron diffraction and Auger electron spectroscopy. The alloy forma tion between Y and Pd leads to different structural and electronic properti es of the surface, which are compared to the switching behavior of the unde rlying Y film when exposed to hydrogen. The electronic structure of the int ermetallic compound YxPd1-x(0 <x <0.25) was studied by angular-resolved ult raviolet photoemission spectroscopy. The samples were prepared by Y deposit ion on Pd (111) surfaces of epitaxial films. The electronic structure of th e alloy is discussed in the framework of a qualitative tight-binding approa ch. The reactivity of the Y-Pd alloy surfaces is estimated using the chemis orption model of Hammer and Norskov [Nature 376, 238 (1995)]. We show that exposure to air leads to an oxygen induced surface segregation of the Y-Pd alloy, which hinders hydrogen adsorption. (C) 2001 American Institute of Ph ysics.