High energy spectroscopies and magnetism

We present a review of high energy spectroscopy (HES) techniques in the field of magnetism, and show that the use of HES techniques can give valuable information on magnetic systems. There is a wide range of HES techniques, so that a large number of parameters relevant to magnetism can be probed. This review will present some illustrations thereof.     

X-ray photoelectron spectroscopy (XPS) of adsorbate valence bands

The CO valence levels for a monolayer of CO adsorbed on the basal (001) face of ruthenium have been observed by XPS. The assignment of the observed peaks is discussed.     

The Ba/Si(100)-2 × 1 interface: II. XPS, BIS and synchrotron PS studies of Schottky-barrier formation

In the preceding paper [Surf. Sci. 260 (1992) 97] we have reported the results of XPS and XAES studies of silicide formation at the Ba/Si(100) interface at elevated temperatures. In this paper we present the results of XPS, BIS, and synchroton PS studies on the same system but at room temperature. We find that Ba grows layer by layer on the Si substrate and that electron energy losses and final state effects are important for the correct interpretation of the data. Observed shifts in the Si 2p core levels are ascribed to a lowering of the Schottky barrier and are explained with the model presented by Mönch [Phys. Rev. Lett. 58 (1987) 1260], while measured shifts in the Ba 4d core levels are related to the reduction of the silicon work function. This model requires the presence of metal induced gap states (MIGS) which are indeed observed with BIS. Here we find increasing spectral intensity near the Fermi level upon Ba deposition. This intensity is assigned to Ba 5d states which probably fulfill the role of the MIGS in Mönch's model.     

Chemical changes induced by sputtering in TiO2 and some selected titanates as observed by X-ray absorption spectroscopy

We studied the chemical changes induced by Ar⁺-bombardment in TiO₂ and some selected titanates by means of soft X-ray absorption spectroscopy. The O 1s and Ti 2p spectra provide unique information on hybridization, valency and crystal-field effects. In TiO₂, we found that some Ti ions are partly reduced but no metallization is observed. On the other hand, the effect of ion-bombardment in titanates depends on the counter-ions. In Al₂TiO₅, the central Ti ions are strongly reduced while Al₂O₃ remains unaffected. In NiTiO₃, by contrast, we found the opposite behaviour with strong reduction of the counter Ni ions. This contrasting behaviour seems to be related to differences in the relative heat of formation of the sub-species. In PbTiO₃, both central- and counter-ions are affected by sputtering. Finally, the electronic structure of BaTiO₃ presents very little changes upon ion-bombardment.     

Valence bands of aluminium noble-metal alloys studied by X-ray photoelectron spectroscopy

The valence bands of aluminium noble-metal alloys are studied by XPS using Al Kα-radiation. The alloys were prepared by evaporation followed by interdiffusion of the components under ultra-high vacuum within the analyzer chamber of the spectrometer. In the absence of surface contamination the alloys exhibit more intense spectra, with sharper features, than those observed for previously studied bulk samples.