T. Lederer
Free University of Berlin
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Featured researches published by T. Lederer.
Surface Science | 1994
M. Tischer; Dimitri Arvanitis; Toshihiko Yokoyama; T. Lederer; L. Tröger; K. Baberschke
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
Chemical Physics Letters | 1993
Dimitri Arvanitis; Comelli G; T. Lederer; H. Rabus; K. Baberschke
Abstract By means of temperature-dependent surface extended X-ray absorption fine-structure measurements, two different chemisorption states of O atoms on a Cu(100) surface were confirmed. From a systematic discussion of N and O on Ni(100) we deduce that for reconstructed substrates the bond is more covalent, for the unreconstructed ones more ionic. For the latter case we can determine the charge transfer to the ad-atom to be 0.92(3) e in agreement with theoretical calculations, based on a Madelung form of the pair potential.
Applied Physics A | 1989
Dimitri Arvanitis; H. Rabus; M. Domke; A. Puschmann; G. Comelli; H. Petersen; L. Tröger; T. Lederer; G. Kaindl; K. Baberschke
Using plane grating, ellipsoidal mirror, grazing incidence monochromators at the storage ring BESSY, a resolution of ≦ 150meV was achieved for a photon energy of 285 eV. This high energy resolution considerably extends the range of possible studies using core level Spectroscopy. Some of the new opportunities are illustrated at the CK edge by resolving the vibrational fine structure of condensed C2H4 multilayers in the (1s−1, π*) state by means of photoabsorption spectroscopy. For the sake of comparison with other high resolution instruments, the vibrational fine structure of condensed N2 multilayers at the NK edge (∼ 400eV) was also measured, yielding a resolving power of 3000.
Journal of Magnetism and Magnetic Materials | 1994
M. Tischer; Dimitri Arvanitis; A. Aspelmeier; M. Russo; T. Lederer; K. Baberschke
Abstract We report Magnetic Circular X-ray Dichroism (MCXD) measurements of ultrathin monolayers (ML) and bulk-like Co films grown on a Cu(100) surface. No increase is observed in the orbital magnetic moment of the Co atoms for the ultrathin films in contrast to expectations due to symmetry lowering on the surface. We developed a new ac field modulated MCXD-susceptibility technique permitting accurate measurements of the critical temperature T c . At about 1.8 ML, T c suddenly increases by more than 150 K when the film structure changes from hetero-to homoepitaxial growth.
Japanese Journal of Applied Physics | 1993
Dimitri Arvanitis; T. Lederer; Giovanni Comelli; M. Tischer; Toshihiko Yokoyama; L. Tröger; K. Baberschke
The temperature dependent Surface EXAFS of O and N on Ni(100) and O on Cu(100) is analyzed. The first moments of the Pair Distribution Function (PDF) are determined, including anharmonic contributions. From a systematic analysis of the pair potentials it is proposed that for the reconstructed surfaces the bond is more covalent, for the unreconstructed ones more ionic. The value of the charge transfer to the adatom is found to be ~0.63 electrons for the ionic cases. Upon the reconstruction of the Cu(100) surface the static part of the disorder is found to increase. The dissociation process of O2 molecules on Cu(100) is studied. The differences in the PDF moments between the different adsorption states are shown to correlate to the strength of chemisorption.
Japanese Journal of Applied Physics | 1993
L. Tröger; Dimitri Arvanitis; J. J. Rehr; T. Lederer; Toshihiko Yokoyama; K. Baberschke; Ehrenfried Zschech
High quality fluorescence yield oxygen EXAFS spectra of Cu2O and CuO demonstrate the transferability of the O-Cu EXAFS phase-shift in contrast to earlier findings. This allows a precise O-Cu distance determination. It is shown for the copper oxides that theoretical calculations by means of the FEFF code yield reliable distance standards also in the soft x-ray region. These advances improve the distance determination by means of oxygen EXAFS and open up cases where reliable experimental standards are not available. Following a discussion of the oxygen EXAFS of NiO, the consequences with respect to the surface systems O/Cu and O/Ni are presented. In particular, a systematic error of +0.05? in previous surface EXAFS distance determinations of O/Ni systems is established.
Physical Review B | 1994
L. Tröger; Toshihiko Yokoyama; Dimitri Arvanitis; T. Lederer; M. Tischer; K. Baberschke
Physical Review B | 1993
T. Lederer; D. Arvanitis; Comelli G; L. Tröger; K. Baberschke
Physical Review B | 1993
T. Lederer; Dimitri Arvanitis; M. Tischer; Comelli G; L. Tröger; K. Baberschke
Physical Review Letters | 1990
L. Wenzel; D. Arvanitis; H. Rabus; T. Lederer; K. Baberschke; Comelli G