THE sp HYBRID BONDING OF C, N AND O TO THE fcc(001) SURFACE OF NICKEL AND RHODIUM

Abstract

This brief review focuses on the nature, kinetics, dynamics and consequences of the sp-orbital hybrid bonding of C, N and O to the Ni/Rh(001) surfaces which give rise to the same kind of "radial and then the p4g clock" reconstruction. It is identified that the "radial" and the subsequent "clock" reconstruction result from the adsorbate–substrate bond formation with sp-orbital hybridization, and that the driving force behind the reconstruction originates from the electrostatic interaction along the <11> direction. At the initial stage, A-1 (A=C, N or O adsorbate) sinks into the fourfold hollow site and forms one bond with a B (B = Ni or Rh host atom) underneath, giving rise to an AB5 cluster with four dipoles at the surface. As A-1 evolves into the hybridized-A-n (n=4, 3, 2), the AB5 cluster evolves into an AB4 tetrahedron. Meanwhile, the AB4 tetrahedron redefines three of the four surface dipoles as B+, B2+, B+/ dipole or Bdipole, depending on the valence value of the adsorbate. The electrostatic force arises upon repopulating the valence electrons, which creates rhombus strings along the <11> direction. With the presence of nonbonding lone pairs, the clock rotation on Ni(00l)-(2×2)p4g-2N-3 and Rh(00l)-(2×2)p4g-2O-2 surfaces is initiated by the alternate attraction and repulsion in the <11> direction and the rotation is stabilized by bond tension; whereas the clock rotation on the Ni(00l)-(2×2)p4g-2C-4 surface is driven by the nonequivalent electrostatic repulsion in the <11> direction and the rotation is balanced by strong bond compression. The findings so far have led to technical innovation for the adhesion between diamond and metals by designing a gradient TiCN transition layer to neutralize the bond stress.