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Dive into the research topics where T. Lederer is active.

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Featured researches published by T. Lederer.


Surface Science | 1994

Temperature dependent MCXD measurements of thin Ni films on Cu(100)

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

Characterization of two different adsorption states for O on Cu(100). Ionic versus covalent bonding

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

High resolution photoabsorption spectroscopy at the carbonK-Edge

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

Local magnetism of Co monolayers: A new type of magnetic circular x-ray dichroism measurement

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

Bonding on Surfaces: The SEXAFS Point of View

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

Improved Distance Determination in Oxygen EXAFS: Soft X-ray Fluorescence Measurements versus Theoretical Standards

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

Determination of bond lengths, atomic mean-square relative displacements, and local thermal expansion by means of soft-x-ray photoabsorption

L. Tröger; Toshihiko Yokoyama; Dimitri Arvanitis; T. Lederer; M. Tischer; K. Baberschke


Physical Review B | 1993

Adsorption of oxygen on Cu(100). I. Local structure and dynamics for two atomic chemisorption states.

T. Lederer; D. Arvanitis; Comelli G; L. Tröger; K. Baberschke


Physical Review B | 1993

Structural determination of c (2×2)N/Cu(100): A multiple-scattering surface-EXAFS study

T. Lederer; Dimitri Arvanitis; M. Tischer; Comelli G; L. Tröger; K. Baberschke


Physical Review Letters | 1990

Enhanced anharmonicity in the interaction of low-Z adsorbates with metal-surfaces.

L. Wenzel; D. Arvanitis; H. Rabus; T. Lederer; K. Baberschke; Comelli G

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K. Baberschke

Free University of Berlin

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L. Tröger

Free University of Berlin

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M. Tischer

Free University of Berlin

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Toshihiko Yokoyama

Graduate University for Advanced Studies

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Comelli G

Free University of Berlin

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H. Rabus

Free University of Berlin

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L. Wenzel

Free University of Berlin

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A. Aspelmeier

Free University of Berlin

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