Formulation Bond Geometry and Atomic Valence

Unlike the nanometric Cu(001)-c(2 x 2)-0 precursor state, in which oxygen forms an off-centered pyramid (4(0 + Cu ) or 20 -I- Cu ) with its surface neighbors, the oxygen adsorbates in the Co(1010)-p(2 x l)-0 phase prefer the atop atomic positions. In contrast, in the 0-(Rh, Pd)(l 10) precursor states, occupies the C2v-hollow site and bonds to the atom underneath first. Obviously, the 0 performs quite differently at these surfaces because of the difference in the scale and geometry of the host lattice and the electronegativity between the host surfaces. 

With increasing oxygen exposure, the evolves into 0 and the oxide tetrahedron forms through a process of rebonding, as shown in Fig. 3.18. The basic quasi-tetrahedron denoted as (1233) is expressed as (B = Ru, Co)  

The honeycomb-like or oval-shaped protrusions in the STM image are composed of four CqP that head toward the center of the oval. In the C02O tetrahedron, the lack of one Co atom for the bond is compensated by the polarized electron cloud (as denoted 2) as do the (Rh, Pd)(110)-c(2 x 2)pmg-20  

The contribution from the electron clouds of the dipoles to the oxide tetrahedron formation in the (Co, Ru)(1010)-(2 x 4)-40 , the (Co, Ru)(1010)-(2 x l)p2mg-20 , and the Cu(110)-c(6 x 2)-80 phases evidences that the ip-orbit hybridization of an 0 is independent of its bonding constituents. Oxygen can bond to any component whether it is an atom or electron cloud of a single or a cluster of dipoles, which is able to supply electrons to fill the hybridized orbital of the oxide tetrahedron. 

The (Co, Ru)(1010)-(2 x l)p2 mg-20 phase, as shown in Fig. 3.19, interlocks with the c(2 x 4)-20 phase by adding the zigzagged 0-0 chains at positions between the pairing-dipole rows. The chemical reaction follows the relationship in the unit cell  

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