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Abstract: To investigate the initial growth of Fe films on Si(0 0 1) and the Fe/Si interface, Fe films at various thicknesses have been systematically studied by soft X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). The Fe L edge XAS spectrum shows a strong thickness dependence with broader line-width for thinner films. Detailed analysis of the Fe absorption signal as a function of the thickness shows that the broad linewidth of Fe L edge XAS spectra is mostly contributed by the first Fe layer at the Fe/Si interface. In contrast to XAS, Fe 2p photoemission spectra for these films are identical. However, valence band photoemission also shows a strong thickness dependence. Comparing the valence band photoemission spectra of the thin Fe/Si(0 0 1) films with that of pure Si and the thickest Fe film, the difference spectra at all thicknesses show almost identical shape indicating the same origin: the Fe/Si interface. Thus, it is mainly the first Fe layer at Fe/Si layer that is reactive with the Si substrate changing its electronic structure. [Copyright &y& Elsevier]

Abstract: Soft-magnetic FeCo alloy nanoparticles with diameters less than 100 nm are prepared by ball milling. X-ray photoemission spectroscopy (XPS) and X-ray magnetic circular dichroism (XMCD) are used to characterize these particles. While the XPS spectrum from the as-prepared sample clearly shows Co photoemission peaks, no sign of Fe is observed in the same spectrum. However, Fe photoemission peaks appear after 1 h of Ar ion sputtering. A quantitative analysis of the XPS spectra shows an increase of Fe concentration versus sputtering time until the Fe:Co ratio of the bulk alloy is reached. In addition, the narrow scan Fe and Co 2p XPS spectra show that Co is more oxidized than Fe. All these measurements indicate that the nanoparticles have a Co shell and an Fe-rich core. They further demonstrate the usefulness of XPS combined with depth-profiling via sputtering to obtain element- and chemically-sensitive structural information on nanoparticles. XMCD as an element-specific magnetic analysis tool further reveals that Fe and Co are ferromagnetically coupled in these particles. The information obtained is useful for establishing a structure–property relation for the studied material that is expected to have applications as a soft magnetic material at high temperatures. [Copyright &y& Elsevier]

In order to test the presence of interatomic multi-atom resonant photoemission (MARPE) in 3d magnetic ultrathin films, 2p photoelectron emission of various ferromagnetic 3d metals was studied while the excitation energy was tuned around the L2,3 core level absorption edge of a different 3d metal. Both elements were in direct contact either as bilayer or as alloys to maximize this possible effect. Systems under study were Fe/Co, Fe/Ni, Fe30Ni70, Co, Co90Mn10, and Ni90Mn10, all grown as epitaxial films on Cu(001). No measurable change in intensity of the 2p photoemission intensities in normal emission for 45° incidence of more than 2.5–5% was found as a result of resonant excitation of neighboring atoms in any of these systems. We can thus exclude the presence of significant MARPE in these metallic systems in the present experimental geometry. This is further confirmed by the photon energy dependence of the linear magnetic dichroism in the Fe 2p photoemission of a Fe/Co film, which is not influenced by Co L2,3 edge resonant absorption. [Copyright &y& Elsevier]

Abstract: The first soft X-ray facility at the Singapore Synchrotron Light Source was built by FMB and commissioned in 2003. Dubbed SINS for surface, interface, and nanostructure science, it covers a photon energy range from 50 to 1200eV. The photon beam can be set to left circular, right circular or linear polarization by changing the pitch and vertical position of the vertical focusing mirror of the prefocusing optics. The typical resolution (E/ΔE) and flux are about 1000 at 1010 photons/s or exceeding 4000 at 108 photons/s in a spot of about 1.5mm×0.2mm on the sample. The performance of the beamline was measured using gas photoionization spectra of Ar, He, Kr, and N2 as well as an XMCD spectrum of a Ni sample. From the Ni XMCD signal, calculation shows that the degree of circular polarization can reach 95% at 850eV photon energy. The end-station is presently equipped with a hemispherical electron energy analyzer and typical surface science diagnostics including LEED and ion sputtering. Upgrading with an in situ STM/AFM and a growth chamber is underway which will make SINS a unique tool for in situ surface and nanoscale science studies. [Copyright &y& Elsevier]