Oxygen adsorption on the Ru(101¯0) surface: Anomalous coverage dependence

Abstract

Oxygen adsorption on to Ru͑10 1 0͒ results in the formation of two ordered overlayers, i.e., a c(2 ϫ4)-2O and a (2ϫ1)p2mg-2O phase, which were analyzed by low-energy electron diffraction ͑LEED͒ and density functional theory ͑DFT͒ calculation. In addition, the vibrational properties of these overlayers were studied by high-resolution electron loss spectroscopy. In both phases, oxygen occupies the threefold coordinated hcp site along the densely packed rows on an otherwise unreconstructed surface. The O atoms are attached to two atoms in the first Ru layer Ru͑1͒ and to one Ru atom in the second layer Ru͑2͒, forming zigzag chains along the troughs. While in the low-coverage c(2ϫ4)-O phase, the bond lengths of O to Ru͑1͒ and Ru͑2͒ are 2.08 and 2.03 Å, respectively, corresponding bond lengths in the high-coverage (2 ϫ1)-p2mg-2O phase are 2.01 and 2.04 Å ͑LEED͒. Although the adsorption energy decreases by 220 meV with O coverage ͑DFT calculations͒, we observe experimentally a shortening of the Ru͑1͒-O bond length with O coverage. The v(Ru-O) stretch mode is found at 67 meV ͓c(2ϫ4)-2O͔ and 64 meV ͓(2 ϫ1)p2mg-2O͔. ͓S0163-1829͑98͒00824-8͔

Oxygen-inducedp(2×3)reconstruction on Mo(112) studied by LEED and STM

“…It is interesting to note that RuO 2 is found to grow with ͑100͒ orientation on the trough-and-row Ru(101 0) surface structure 48 where oxygen adsorption has been proven to take place in the herepostulated threefold hcp adsorption sites. 46 If the situation for the MoO 2 growth on Mo͑112͒ is similar, then the herestudied oxygen-induced surface reconstruction of the Mo͑112͒ surface can indeed be regarded as a precursor state of the MoO 2 lattice. The surface reconstruction provides the trigonal coordination sphere of the oxygen atoms in the MoO 2 lattice in the form of the hcp adsorption sites.…”

“…This idea results from many studies on oxygen adsorption on transitionmetal surfaces 18 and an example is given by the appearance of the structure c(4ϫ2)-2O-Ru(101 0) before, at higher O coverages, Ru atoms are shared in the (2ϫ1) p2mg-2O phase. 46 That oxygen atoms are not willing to do so before the O coverage is substantially increased, can again be understood in the EMT framework. Competition for the same charge density will force the oxygen atoms in search for the ''optimum'' charge density to approach closer to the surface that will raise the elastic lattice energy by distorting the adsorption site environment.…”

Oxidation electronics: bond–band–barrier correlation and its applications

“…Furthermore, chemisorption of oxygen causes a significant expansion ($ 25%) of the first Co interlayer spacing and a slight contraction ( $ 5%) of the second Co interlayer spacing with respect to those of the bulk. A LEED, DFT and HREELS study conducted by Schwegmann et al [63] consider this less-ordered p(2Â1)-O phase as the precursor state because we have found, using VLEED, that the annealing supplies a disturbance rather than a driving force to enhance the reaction and that the O-Cu bonding processes are reversible [99]. À2 structure [63].…”

“…A LEED, DFT and HREELS study conducted by Schwegmann et al [63] consider this less-ordered p(2Â1)-O phase as the precursor state because we have found, using VLEED, that the annealing supplies a disturbance rather than a driving force to enhance the reaction and that the O-Cu bonding processes are reversible [99]. À2 structure [63]. A tetrahedron is framed by a dotted square.…”

“…High-resolution EELS from O-Ru [63,64] and O-Rh surfaces showed that the stretch modes of dipole vibration were around $ 0.05 eV energy. The peak shifts towards higher binding energy when oxygen coverage increases.…”