Structural, electronic, and magnetic properties of clean and Ag-covered Fe monolayers on W(110)

Oxygen on an Fe monolayer on W(110): From chemisorption to oxidation

The adsorption of oxygen on a pseudomorphic iron monolayer deposited on a W(110) surface was studied experimentally and theoretically. Standard surface characterization methods, such as Auger electron spectroscopy and low energy electron diffraction, and specific nuclear methods, such as conversion electron Mössbauer spectroscopy (CEMS) and nuclear resonant scattering of synchrotron radiation, combined with theoretical calculations based on the density functional theory allowed us to determine the structure of the oxygen adsorbate and the electronic properties of iron atoms with different oxygen coordinations. The oxygen-(3 × 2) structure on the iron monolayer was recognized and was interpreted to be a state with oxygen chemisorbed on the non-reconstructed surface with modest electron transfer from iron to oxygen. A transition from chemisorbed oxygen to the onset of Fe-oxidation is revealed by distinct changes in the CEMS spectra.

Optical reflectance anisotropy of the growth of Fe monolayers on W(110)

We report measurements of the optical anisotropy of Fe layers grown on the W(110) surface using reflection anisotropy spectroscopy (RAS). As the first monolayer of Fe is deposited onto W(110), the resonance-like RAS profile of the clean surface is reduced in intensity. We find evidence for the surface state on W(110) surviving as an interface state following Fe deposition. We observe an anisotropic optical response from Fe layers grown on top of the first two monolayers, where a broad peak at 3 eV dominates the RAS response. The results are simulated in terms of a layered Fresnel reflection model incorporating either a strained Fe overlayer or an Fe overlayer whose dielectric properties are approximated by a simple Lorentzian oscillator. Both approaches are found to produce simulated RA spectra that are in good agreement with experiment. The former approach provides evidence that RAS can detect anisotropy in strained overlayers and that 7 ML films have bulk-like electronic and optical properties.

Soft X-Ray Photoelectron Spectroscopy Of Bi-Metallic Interfacial Bonding

We report the first application of Soft X-ray Photoelectron Spectroscopy (SXPS) to probe the bonding at epitaxial, bi-metallic interfaces with atomic-layer spatial selectivity. Specifically, we have measured the W(4f)7/2 levels of interfacial tungsten atoms for (1×1)Fe/W(110), (1×1)Ni/W(110), and (1×1)PtW(110). For clean W(110), the surface atoms exhibit a W(4f)7/2 peak at -320 meV binding energy with respect to the bulk W(4f)7/2 peak. Upon formation of the metallic overlayers, the interfacial tungsten atoms contribute W(4f)7/2 peaks at -225 meV (Fe/W), -140 meV (Ni/W), and +70 meV (Pt/W) with respect to the bulk W(4f)7/2 peak. The systematic reduction in the binding energy difference between interfacial and bulk tungsten atoms for Fe, Ni, and Pt correlates with increasing heats of adsorption on W(110), as determined by Temperature Programmed Desorption. This suggests that SXPS, in combination with first principles calculations and Born-Haber thermochemical cycle analyses, can be used as a non-destructive probe of bi-metallic interfacial bonding energies.