Oxygen Adsorption on the Fe(110) Surface: The Old System – New Structures

Abstract

Adsorption of oxygen on the (110) surface of epitaxial iron films on tungsten (110) was studied using lowenergy electron diffraction (LEED), low-energy electron microscopy (LEEM), and Auger electron spectroscopy within an exposure range of 0−300 Langmuir (L). Selected oxygen adsorption structures on Fe(110) reported in the literature were critically compared and revised in reference to the present study. The initial adsorption of 1/4 oxygen monolayer resulting in the commonly observed (2 × 2) structure was followed by a structure that was frequently termed as (3 × 1). Its complex LEED pattern was ultimately resolved and interpreted as originating from two structural domains of a large oblique unit cell (eight times larger than the substrate unit cell) and 3/8 oxygen coverage. A new (3 × 2) structure was identified at a coverage of 2/3. The domain interpretation of last two structures was verified by LEEM and confirmed by density functional theory calculations. The onset of oxygen−iron bonding formation was recognized by the change in the symmetry of the LEED pattern and the shape of the iron AES signal. Finally, the formation of an iron oxide FeO(111) monolayer was evidenced at the oxygen exposure of ∼300 L.

Controlling the Electronic and Structural Coupling of C60 Nano Films on Fe(001) through Oxygen Adsorption at the Interface

“…This phenomenology is quite different with respect to that typically observed upon deposition of transition metals on the Fe(001)- p (1 × 1)­O, where oxygen floats on top of the growing film. − Recently, the occurrence of oxygen buried at the interface has been observed in the case of NaCl films deposited on the Fe(001)- p (1 × 1)O substrate . In the low kinetic energy region (see Figure b), the Fe MVV transition is characterized by a metallic peak at about 46 eV and by a shoulder at lower kinetic energy, related to the presence of Fe–O bonds. − The shoulder is present also after C 60 deposition, confirming that the Fe–O bonds are preserved. The low energy electron diffraction patterns acquired on 0.8 ML C 60 /Fe­(001)- p (1 × 1)O (not shown) are characterized by the same square symmetry of the Fe(001)- p (1 × 1)O surface, suggesting that the oxygen atoms retain a well-ordered p (1 × 1) structure with respect to the substrate also after C 60 deposition.…”

“…55 In the low kinetic energy region (see Figure 4b), the Fe MVV transition is characterized by a metallic peak at about 46 eV and by a shoulder at lower kinetic energy, related to the presence of Fe−O bonds. 56−60 The shoulder is present also after C 60 O is detected at 2.4 ± 0.05 eV below the Fermi level (E F ), while the LUMO and LUMO+1 orbitals are placed at 0.9 ± 0.05 and 2.2 ± 0.05 eV above E F , respectively. In the case of C 60 islands nucleated on the Fe(001)-p(1 × 1)O substrate, the HOMO is 2.6 ± 0.05 eV below E F , and the LUMO (LUMO+1) is 0.8 ± 0.05 (2.1 ± 0.05) eV above E F .…”

Fabrication of Isolated Iron Nanowires

“…An atomically resolved image of the surface of the pseudohexagonal island in Figure 1 B is displayed in Figure 1 C. The surface is composed of regular parallel rows of bright atomic-scale features aligned in the [001] direction of TiO 2 (110) and parallel to the long growth direction of the nanowires and resembles a modified Fe(110)-O “A” surface formed by O 2 adsorption on Fe(110), as described by Freindl et al 17 The atomic-scale surface structure of the nanowires was observed in STM to be identical to that of the pseudohexagonal islands (see Figure S3 ). The presence of O on the surface of the nanostructures is expected due to facile migration/spillover of oxygen from the TiO 2 (110) substrate promoted by the elevated temperature during deposition, a clear indication of a strong metal support interaction (SMSI).…”

Incipient FeO(1 1 1) monolayer formation during O-adsorption on Fe(1 1 0) surface

“…conducted a combined DFT and experimental study [35]. They discovered a new (3×2) phase using LEED, corresponding to a 0.67 ML coverage, and verified its existence using DFT.…”

“…They deduced that O atoms adsorb at long-bridge (lb) sites for low exposure, with a single vibration at around 500 cm Theoretical calculations using density functional theory (DFT) of the adsorption of O atoms on the Fe(110) surface were first reported in the early 2000s. These DFT studies primarily investigated the (2×2), (3×1) and (1×1) geometries [29][30][31][32][33][34][35]. There is consensus in the literature regarding the adsorption energy, which linearly increased from ~1.40 eV to 3.50 eV per O atom from low to high coverage [30,34].…”