First Test of the VOLPE Project at the ESRF: VOLume Sensitive PhotoEmission from Solids using Synchrotron Radiation

16-06-2004

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Since the first experiment performed in the 50's by Siegbahn (Nobel price in 1981) and co-workers, the PhotoEmission (PE) technique (known with different acronyms XPS, ESCA, PES etc.) is one of the most powerful spectroscopic tools to investigate electronic properties and is characterised by strong surface sensitivity (< 10 Angstrom), an aspect fully exploited in the last four decades for studying the topmost atomic layers is solids and interfaces. However, the presence of the surface, i.e. the reduced dimensionality and the broken symmetry that the surface represents, often prevents us from obtaining information on the bulk. Important examples of this difficulty can be found in the analysis of strongly correlated systems, as high temperature superconductors and heavy fermions systems. Even at the highest electron kinetic energies normally analysed (up to 2 keV), the PE process is still surface sensitive, which turns into a limitation if bulk sensitivity is what one is seeking.

The aim of the EU-RTD VOLPE (VOLume PhotoEmission from solids) project, joining five different institutions in Switzerland, France and Italy from December 2001 to November 2004, is to measure the volume electronic properties of solids via Photoemission using Synchrotron Radiation, fully exploiting the high brilliance of the ESRF beam.

The VOLPE setup was assembled at the ESRF in January 2004 and installed in February 2004 on beamline ID16 for a first experiment.

The main results are:

  1. A negligible contribution of the signal coming from the surface, as revealed from the intensity measured on the d and s bands of Ag without any preparation of the sample (neither scraping nor sputtering), in a 10-7 mbar vacuum.
  2. PE spectra with good statistics and sufficient energy resolution, when compared to the results of standard PE experiments carried out in surface sensitive mode.
  3. Bulk sensitivity at about 5 keV and 7 keV kinetic energy, measuring 2p core level emission from Co buried under a capping layer 120 Å thick.
  4. An overall energy resolution (photons + analyser) of 125 meV, measured on the Fermi level of polycristalline Ag.

 

 

Fig. 1: Ag valence band and Fermi level as measured at h=5925 eV.

 

 

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Fig. 2: Ag 3d core level as measured at h=7987 eV.

 

 

 

Authors
G. Panaccione (a), G. Cautero (b), R. Tommasini (b), P. Lacovig (b), M. Cautero (b), B. Krastanov (b), P. Pittana (b), G. Paolicelli (c), F. Offi (c), A. Fondacaro(c), G. Stefani (c), P. Torelli (d), M. Sacchi (d), M. Grioni (e), G. Monaco (f), C. Henriquet (f), S. Huotari (f), G. Vankó (f), R. Verbeni (f).
(a) Lab. TASC INFM, Trieste (Italy)
(b) Sincrotrone Trieste S.C.p.A. (Italy)
(c) Dip. Fisica Univ. Rome III (Italy)
(d) Lab. LURE, Orsay (France)
(e) EPFL (Switzerland)
(f) ESRF (France)

Top image: VOLume Sensitive PhotoEmission from Solids