Comparison of Features for Au and Ir Adsorbed on the Ge (110) Surface*

Single atoms of Au and Ir adsorbed, respectively, on the Ge(110) surface are studied by a first-principles algorithm based on density functional theory. The surface is modeled by a slab consisting of 108 Ge atoms with a 10 Å vacuum region. Hydrogen atoms are used to saturate the dangling orbitals at the other side of the vacuum region. The relaxed surface with the Au or Ir adatom shows the following distinct features: (1) Au is located at the top of the surface while Ir is located below the top layer of the Ge atoms, as a results of the smaller 1.423Å atomic radius of Ir vs. 1.503Å for Au. (2) No bond formation occurs between the metallic adatoms and the Ge atoms because the more tightly bound nature of the d-states in the metal elements do not allow hybridization to form sp³-type directional orbitals, as seen in charge density plots. (3) The Ir charge density is more deformed than Au, because the partially filled d-shell in Ir can be more easily polarized than the completely filled d- states of Au. Comparisons will be made to Ir/Ge(111) and Au/Ge(110) data measured by STM and LEEM.