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We have made in situ investigations of epitaxial ultrathin Fe films on Ag(100). This system is known to exhibit a reorientation of the magnetization, dependent of Fe thickness and temperature. Our aim here is to correlate the local structure with the magnetic properties of this system. The X-ray absorption fine structure has been recorded in situ both in the near edge as well as in the extended X-ray absorption fine structure (EXAFS) range. Using X-ray magnetic circular dichroism we find that, below 300 K, films between 2 and 6 monolayers show an out-of-plane remanent magnetization whereas for thicker films the magnetization lies in-plane. By making use of the Fe L-edge EXAFS we obtain information on the local structure around the Fe atoms, such as the interatomic distances, the coordination number, and the mean square relative displacement of the first neighbor shells. (C) 2003 Elsevier Science B.V. All rights reserved. (Less)

The interaction of a monolayer and submonolayer N2O with the Cu(1 0 0) and Ag(1 1 0) surfaces has been studied using near-edge X-ray absorption fine structure spectroscopy. From a detailed analysis of the angular dependent intensity of the molecular resonances we derive a substrate and coverage dependent bent of the N2O molecules upon adsorption. From the comparison of the π* resonance intensity from the terminal Nt, and central Nc nitrogen atoms we conclude that the N2O molecules couple with the Cu surface through the terminal Nt atom in contrast to the Ag surface where the Nc atom is involved.

We report temperature- and angular-dependent surface extended X-ray absorption fine structure spectroscopy (SEXAFS) measurements of the p4g(2 x 2)C/Ni(100) system. Both a Ni(100) single crystal and ...

High-resolution photoabsorption spectra at the N 1s→π∗ resonance of N2 physisorbed on the Cu(100) surface are reported. The vibrational fine structure of this resonance could be resolved, allowing the determination of the vibrational constants, the lifetime and intramolecular distances of the core-excited states of the physisorbed molecules. The obtained fundamental vibrational constants are compared with the corresponding vibrational parameters for the gas phase.

We present soft X-ray magnetic circular X-ray dichroism (MCXD) measurements at the Ni L edges of thin Ni films on Cu(100) with a thickness between 1 and 7 monolayers. The data were measured around the L 3 edge covering the whole temperature range up to the critical temperature. Furthermore, measurements around both the L 3 and L 2 edges were performed at low temperatures. The temperature variation of the MCXD signal and the critical temperatures of the films as a function of their thickness are discussed and compared to results of other studies

A refined NEXAFS analysis of ethylene physisorbed, chemisorbed and condensed on Cu(100) and Ag(100) will be given. Through deuteration we clearly identify CH and CC vibrations. Applying a simple linear coupling model the Franck-Condon factors for the core excitation process are derived. The only fit parameters are ħω and one single intensity factor S for each vibrational progression, and one linewidth γ for all lines. Form these, we determine the change in bond length for the molecules in the excited state and the decrease of the core hole lifetime upon increasing strength of chemisorption. From the change of the S factors upon chemisorption we determine the force constant that couples the molecule to the substrate. The approach of our analysis will be compared to the recent calculation by Gaeda et al.

The position of the π and σ resonances in the C K edge spectra are determined for multilayer and submonolayer coverages of C2H2, C2H4 and C2H6 at 60 K, on a Cu(100) surface. The majority of the molecules are found lying flat on the surface in submonolayer coverages. We determine an elongation of the C-C bond length, for C2H2 and C2H4 on Cu(100) of 0.21(2) A and 0.10(2) A respectively, using the position of the σ resonance on a common energy scale with the gas phase. The results are compared with the ones of strong chemisorption on Pt(111). The σ-shape resonance of C2H6 chemisorbed on a metal substrate is reported for the first time. The molecule shows no elongation.

We report the first X-ray absorption fine structure measurements above the carbon K-edge recorded by fluorescence detection (FD). Studies for ethylene chemisorbed on Cu(100) were carried out with high-flux ( > 1010 photons/s) synchrotron radiation using an ultra-high vacuum compatible proportional counter. Our results show that K-edge studies by means of FD allow the measurement of extremely dilute concentrations of C corresponding to about 0.02 monolayers on the surface or 20 ppm in the bulk.