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

High-Resolution X-ray Photoelectron Spectroscopy of an IrO2(110) Film on Ir(100)

“…The intense peak at 61.7 eV is attributed to 6-fold coordinated Ir atoms (Ir 6f ) in the IrO 2 bulk and surface; the small peak at 60.8 eV is assigned to bulk Ir metal underneath the IrO 2 film as discussed above, and the peak at 61.3 eV is assigned to the 5-fold coordinated Ir cus atoms at the surface. The peak attributed to Ir cus atoms exhibits a core-level shift (CLS) of −0.4 eV relative to the main peak for Ir 6f atoms, in good agreement with the CLS of −0.7 eV predicted from DFT calculations (Table ) and a prior study . The intensity of the peak at 61.3 eV also increases with decreasing photoelectron kinetic energy (Figure S5 and Table S4), consistent with the assignment of this peak to surface Ir cus atoms.…”

“…XPS demonstrates that a thick IrO 2 film was generated on Ir(100) during oxidation in ∼3 Torr of O 2 at 775 K, in good agreement with prior results. , Ir 4f spectra obtained from the clean Ir(100) substrate exhibit an Ir 4f 7/2 peak at 60.8 eV arising from Ir atoms in the bulk metal as well as a component near 60.3 eV that originates from surface Ir atoms (Figure ); the peak from surface metal is more intense in the Ir 4f spectrum obtained at lower electron kinetic energy (∼190 vs 660 eV) as expected, and its binding energy lies close to that reported previously for clean Ir(100) (see the Supporting Information). After oxidizing the Ir(100) surface, the Ir 4f spectrum exhibits a dominant Ir 4f 7/2 peak at 61.7 eV, shifted by about +0.9 eV relative to metallic Ir, in good agreement with prior reports of the Ir 4f 7/2 binding energy for IrO 2 . − ,− The Ir 4f spectra obtained from the IrO 2 (110) film exhibit strong asymmetry that arises from shakeup processes during photoelectron generation (section S2); this characteristic of the core-level spectra is intrinsic to IrO 2 . , …”

Kinetics of the Thermal Oxidation of Ir(100) toward IrO2 Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy

“…O Ot -terminated as long as the sample is exposed to 1 mbar of O 2 . 10,27 The resulting ratio is still slightly higher than the expected 2:1 oxygen to iridium ratio in IrO 2 which can be caused by a number of effects, such as, e.g., X-ray photoelectron diffraction (XPD) effects. 24 For example, our previous XPD measurements on an isomorphic rutile RuO 2 (110) surface showed azimuthal intensity modulations of 15% for O 1s and 5% for Ru 3d for a polar emission angle of 30°.…”

“…If a model of stoichiometric IrO 2 (110) is used instead, the calculated average atomic ratio is 2.8 ± 0.1, which is unrealistic. Thus, the model of oxygen-rich IrO 2 (110) was chosen since the surface is expected to be O Ot -terminated as long as the sample is exposed to 1 mbar of O 2 . , The resulting ratio is still slightly higher than the expected 2:1 oxygen to iridium ratio in IrO 2 which can be caused by a number of effects, such as, e.g., X-ray photoelectron diffraction (XPD) effects . For example, our previous XPD measurements on an isomorphic rutile RuO 2 (110) surface showed azimuthal intensity modulations of 15% for O 1s and 5% for Ru 3d for a polar emission angle of 30°.…”

Structural phase transition associated with van Hove singularity in 5d transition metal compound IrTe2

“…A set of peaks (labeled as A in figure 1(b)) induced by the spin-orbit coupling is observed above T s . The binding energy (E B ) of Ir 4f 7 2 in IrTe 2 is 60.3 eV at 300 K, which is obviously lower than in IrO 2 (62.0 eV, Ir 4+ ) [21] and CuIr 2 S 4 (∼61.0 eV, + Ir 3.5 ) [22]. This suggests that the valence of Ir in IrTe 2 is less than +3.5 in the high temperature phase.…”