Stability, structure, and electronic properties of chemisorbed oxygen and thin surface oxides on Ir(111)

Abstract

We present ab initio calculations for atomic oxygen adsorption on Ir͑111͒ for a wide range of oxygen coverages, ⌰, namely from 0.11 to 2.0 monolayers ͑ML͒, including subsurface adsorption and thin surfaceoxide-like structures. For on-surface adsorption, oxygen prefers the fcc-hollow site for all coverages considered. Similarly to oxygen adsorption on other transition metal surfaces, as ⌰ increases from 0.25 ML to 1.0 ML, the binding energy decreases, indicating a repulsive interaction between the adsorbates. For the coverage range of 0.11 to 0.25 ML, there is an attractive interaction, suggesting the possible formation of a local ͑2 ϫ 2͒ periodicity with a local coverage of ⌰ = 0.25 ML. Pure subsurface oxygen adsorption is found to be metastable and endothermic with respect to the free O 2 molecule. For structures with coverage beyond one full ML, we find the incorporation of oxygen under the first Ir layer to be exothermic. As the subsurface O coverage increases in these structures from 0.5 to 1.0 ML, the energy becomes slightly more favorable, indicating an attractive interaction between the O atoms. The structure with the strongest average O binding energy is however a reconstructed trilayer-like structure that can be described as a ͑ ͱ 3 ϫ ͱ 3͒R30°oxide-like layer in p͑2 ϫ 2͒ surface unit cell, with coverage 1.5 ML. Through calculation of the surface Gibbs free energy of adsorption, taking into account the pressure and temperature dependence through the oxygen atom chemical potential, the calculations predict only three thermodynamically stable regions, namely, the clean surface, the p͑2 ϫ 2͒-O phase, and bulk IrO 2 . Thin trilayer surface oxide structures are predicted only to form when kinetic hindering occurs, in agreement with recent experimental work.

Understanding intercalation structures formed under graphene on Ir(111)

“…1(a) and are also given in Table I. In agreement with a previous computational study [41], we find on the clean Ir surface that the potential energy increases (corresponding to a decrease in stability) when the O coverage is increased from 0.25 to 0.50 ML. In the same study, the authors found also an increase in potential energy for coverages lower than 0.25 ML.…”

Deoxygenation of IrO2(110) surface: Core-level spectroscopy and density functional theory calculation

“…And E O/surf stands for the total energy of the oxygen adsorbate on the surface. This definition is the same with the one used in DFT calculation of binding energy for adsorbed oxygen on Ir(1 1 1) [15].…”

“…This binding energy value of O top is slightly higher than the binding energy value of 4.21 eV, which is a sum of the adsorption energy of oxygen atom 1.17 eV [4] for single O-Ir-O trilayer (6 Â 6) surface oxide on Ir(1 1 1)À(7 Â 7) and the binding energy of O 2 3.04 eV/O atom [15]. Hence, it is impractical to subtract two separate O top atoms and combine them in the gas phase.…”

Oxygen orders differently under graphene: new superstructures on Ir(111)

“…Low energy electron diffraction (LEED) of the ordered ad-layer displays a diffraction pattern with a (2 × 2) periodicity. [23][24][25][26] Already early work interpreted the (2 × 2) LEED pattern to be the result of the superposition of three O-(2 × 1) superstructure domains consistent with a room temperature saturation coverage of 0.5 ML with respect to the Ir surface atom density. [23][24][25][26] Already early work interpreted the (2 × 2) LEED pattern to be the result of the superposition of three O-(2 × 1) superstructure domains consistent with a room temperature saturation coverage of 0.5 ML with respect to the Ir surface atom density.…”

“…[32][33][34] Oxygen binds strongly to the Ir(111) substrate with an energy gain of more than 4 eV per oxygen adatom (referred to the energy of a free oxygen atom) [23][24][25][26] and, because it is saturated by its strong bond to Ir, binds only weakly to Gr. [32][33][34] Oxygen binds strongly to the Ir(111) substrate with an energy gain of more than 4 eV per oxygen adatom (referred to the energy of a free oxygen atom) [23][24][25][26] and, because it is saturated by its strong bond to Ir, binds only weakly to Gr.…”