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ALOISA Beamline

ALOISA - Advanced Line for Overlayer, Interface and Surface Analysis

ALOISA is a multipurpose beamline dedicated to SURFACE SCIENCE studies. The ultra-wide energy range (130-1500 eV and 2800-8000 eV) of the beamline and the complete set of detectors in the end-station, allow the users to combine in-situ both structural and chemical investigation techniques, such as:
- X-ray Photoemission Spectroscopy, XPS
- Photoelectron Diffraction, PED
- Resonant X-ray Photoemission Spectroscopy, RESPES
- Resonant X-ray Photoelectron Diffraction, RESPED
- Near Edge X-ray Absorption Fine Spectroscopy, NEXAFS
- Surface X-Ray Diffraction, SXRD
- Auger-Photoelectron Coincidence Spectroscopy, APECS

The HASPES branch line exploits the low energy section of the dispersive system and offers a flexible output for coupling to users owned instrumentation. At present, the branch line is equipped in alternative:
- with a fluorescence detector for XAS study at the K-edge of low-Z dopants in solids (contact: Prof. Federico Boscherini, Univ. of Bologna, e-mail: federico.boscherini@unibo.it).
- with a Helium Atom Scattering apparatus, where it is possible to perform in real time He diffraction and XPS (contacts: Luca Floreano, CNR-IOM; Alberto Morgante, Univ. Trieste; Dean Cvetko, Univ. Ljubljana. See Aloisa staff and collaborators)



The Grating-Crystal Monochromator

A peculiar monochromator has been developed which covers a very wide energy range from 130 eV to 8000 eV. The light is produced by a wiggler/undulator insertion device, selected in angle by a pinhole and collimated by a paraboloidal mirror in sagittal configuration. The parallel light beam impinges on the energy dispersing device which can be selected to be a plane mirror - plane grating for the low energy range (130-1500 eV) or Si channel-cut for the high energy range (2800 to 8000 eV).

The light is focused onto the exit slits by a second paraboloidal mirror and refocused at the centre of the experimental chamber by a toroidal mirror. In the low energy range, thanks to the sagittal configuration of the mirrors and the small emittance of the source, the monochromator reaches high resolutions (see table) with a resolving power higher than 10000 in the energy region around 400 eV. In the high energy region, covered by the Si(111) crystal, the resolving power is about 7500. The spot size at the centre of the experimental chamber is 20-30x150-200 µm. The flux at the sample is above 1011 photon/s for a resolving power exceeding 5000 in the low energy range. A flux of around 5x1010 photon/s is typical in the high energy range.
 


 




The experimental chamber hosts six emispherical electron energy analysers, one of them (66 mm mean radius) with ~2 degrees angular resolution and two angular degrees of freedom. Also two photon detectors are available working in counting mode for Grazing Incidence X-ray Diffraction (GIXD). The sample is mounted on a high resolution manipulator with six degrees of freedom. The preparation chamber offers four deposition cells in a liquid Nitrogen cooled flange (Knudsen cells and electron bombardment cells), a RHEED system, a sputter gun, a fast entry system for rapid change of the sample.

The combination of GIXD and photoelectron diffraction allows fast and reliable structural determination of in situ grown films. Moreover the growth can be monitored in real time by RHEED. The very wide range of geometrical configurations of the sample manipulator + detection system allows Photoelectron Diffraction measurements in near node geometry.

The possibility to perform resonant spectroscopies and Auger Photoelectron Coincidence Spectroscopy (APECS) is an efficient way of studying complex Auger lines. Angle resolved APECS is a unique feature of the beamline.



Experimental chamber instrumentation

  • AXIAL FRAME
    • 5 electron analysers (33 mm mean radius; resolution: 50 meV; acceptance angle 2°) for APECS.
    • 1 phosphorum plate with CCD camera for 2D reflectivity measurements and sample alignment
  • BIMODAL FRAME
    • 1 electron analyzer (66 mm mean radius) equipped with a 2D-delay line detector for XPS and PED
    • 1 energy resolved photodiode for surface X-ray diffraction (SXRD)
    • 1 channeltron for partial yield measurements (XAS)
    • 2 total current photodiodes for in-plane X-ray diffraction and reflectivity
  • PREPARATION CHAMBER
    • Sample transfer system with fast entry-lock;
    • RHEED apparatus;
    • MBE cryopanel with 4 slots for Knudsen and electron bombardment evaporators, 2 quartz microbalances, shutters;
    • ion gun;
    • gas line.
  • MANIPULATOR
    • six degrees of freedom (0.004° accuracy for azimut and incidence angles)
    • main rotation arm coaxial to the photon beam for free orientation of the surface with respect to the photon polarization at constant grazing angle
    • temperature range 150-1100 K

 




rotating element rotation axis extension resolution
Experimental Chamber SR beam ±120° 0.00015°
Axial Frame SR beam ±120° 0.0002°
Bi-modal Frame perpendicular to the SR beam ±100° 0.0002°
Sample Holder SR beam -90˚; +185° 0.001°
Sample Holder grazing angle -2°; +15° 0.001°
Sample Holder surface normal ±95° 0.001°



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Last Updated on Tuesday, 07 May 2013 10:33