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Experimental techniques available
- High Resolution Photoemission
Many important phenomena in condensed-matter physics are determined by the low binding energy electronic states. Very recently, the combination of third-generation synchrotron sources with the last developments in the field of electrons analysers has offered information about these low-energy excitations near the Fermi level.
- Angle-Resolved Photoelectron Spectroscopy (ARPES)
Photoemission spectroscopy is known as a powerful technique to directly probe the occupied electronic structure, bonding and chemical nature of a material. In an ARPES experiment, besides the kinetic energy (E) of the ejected photoelectrons one measures their momentum (k). In this way, one obtain information not only about the energy distribution, but also about the band structure E(k). For more details, see a recent
review , by A. Damascelli et al.
- Resonant Photoemission Spectroscopy
Photoemission spectroscopy near Mn 3p-3d threshold can provide information about the electronic structure. For 3d transition metal compounds, the 3d photoemission is strongly enhanced when the energy of the incoming light equals the energy necessary to excite an electron from the 3p core level to the unoccupied 3d state. The intermediate excited state may decay into a final state identical to that obtained after (direct) photoemission of the 3d electrons. The interference of the two processes is denoted as resonant photoemission (RPES) at the 3p-3d threshold. Example:
resonant photoemission of single crystalline manganites .
To map Fermi surfaces directly one measures the intensities of the photoelectrons emitted as a function of emission angles to the crystal axes, and thus of the momentum component k parallel to the surface. At positions where a band crosses the Fermi level, the photoemission intensity at the Fermi edge rises sharply, contributing to the measured contour of the Fermi surface map. Example:
Ni (111) by M. Hoesch et al.
- Spin-Dependent Photoemission/ Complete Photoemission (COPHEE)
The COPHEE spectrometer at the SIS beamline consists of a high resolution electrostatic hemispherical electron energy analyser equipped with a pair of 50 kV classical Mott detectors. The two Mott detectors in the COPHEE instrument are mounted such that the out-of-plane component of the polarization can be measured directly within the small angular range of ±7 covered in the experiment. The in-plane component is accessible by both polarimeters, with a 45 inclination of the sensitive axes with respect to the in-plane transverse direction of the spin polarization. The polarimeter is sensitive to all three components of the polarization vector. The sample is mounted on an in-vacuum sample goniometer for the free rotation about an axis in the surface plane and around the surface normal, which allows the measurement of spectra for any emission angle above the surface. For more informations, see
Dissertation,
by M. Hoesch, Univ. Zurich, 2002
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- Low Energy Photoelectron Diffraction
- X-Ray Absorption Spectroscopy (XAS) - soon available
- X-Ray Emission Spectroscopy (XES)
The end-station of the Surface/Interface Spectroscopy (SIS) beamline was recently extended with the implementation of an X-ray emission spectrometer XES-350 produced by Gammadata Scienta. The experimental setup allows the performing of both high-resolution Angle Resolved Photoemission (ARPES) and Resonant Inelastic X-ray Scattering (RIXS) in the same main chamber, thus offering a unique tool for the investigation of the electronic structure in advanced materials. X-ray emission is a powerful “photon-in photon-out” experimental method which delivers element sensitive information on the occupied part of the band structure. Tuneable high-intensive synchrotron radiation is employed to generate selected core-holes which then decay either through electron or light emission. The information contained in spectral features can range from direct band structure information, partial density of states to information on correlation effects.
Research examples
First test-experiments at SIS beamline
F. Clerc et al., First experiments at the SIS beamline: ARPES on quasi-2D materials (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 47)
C. Sondergaard et al., The electronic structure of ZrTe3 (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 43)
Research examples during the first few months of user-operation
F. Baumberger et al., Observation of a step induced gap in the Fermi surface of vicinal Cu (443) (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 61)
M. C. Falub et al., Electronic structure of LA1-xSrxMnO3 single crystals (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 46)
M. Hoesch et al., Fermi surface mapping on ultrathin films of Ni/Cu(001)(PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 49)
K. Hricovini et al., Polarizations dependent surface states on InAs (100) (8x2) (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 48)
A. Scheybal et al., Dispersion and interaction of molecular and metallic electrons at the interface C60/Ag(111) (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 45)
A. Scheybal et al., Shockley tupe surface state vs. LUMO: the interaction of C60 and Ag(111) (PSI-Scientific Report 2002, Vol. VII, Synchrotron Radiation/Micro- and Nanotechnology, ISSN 1660-4709, March 2003, PSI Villigen, p. 98)
Research examples during 2003
PSI-Scientific Report 2003, soon available at http://www.psi.ch/news_events/news_events_info_material.shtml
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Beamline status
