Info for Users

Here you'll find info for users

Proposal Submission

- Since 2014, the fluorescence detector for XAS is no longer available at the branchline.
- The branchline endstations (HASPES and ANCHOR) are not open to public access.

NEW POLICY: The Users must contact in advance the beamline responsible to evaluate 1) the proposal feasibility and 2) the most appropriate Review Panel. The local contact can also help the Users to single out which alternative beamlines are better suited to their requirements.

We encourage Users and collaborators to discuss their proposals with the beamline local contacts before the submission deadline. This is very important for a careful assessment of the experiment feasibility and may lead to improvements in the proposed experimental plan. For the proposal submission procedures see  http://www.elettra.trieste.it/UserOffice/

Sample holder

- only one sample at a time (due to grazing incidence with manipulator coaxial to the x-ray beam);
- ideal sample: circular, Ø 10 mm (minimum 5 mm due to grazing geometry);
- mounting: Mo clips on lateral notches (2 to 3 mm thickness), surface must be fully exposed;
- heating: either radiative (max 850 K) or electron bombardment (max 1100 K); 2 Cr-Al thermocouples;
- cooling: LN2 cold finger (minimum 140-150 K);

 

Spectroscopic measurements @ ALOISA

XPS
- grazing incidence (typically 4-6˚)
- free emission angle, by spectrometer rotation from normal to horizon (acceptance angle ~2˚)
- free surface orientation with respect to electric field from p to s polarization
  (by sample rotation around the beam axis at constant grazing angle)
- optimal software for Resonant XPS
LIMITS:
- minimum useful photoelectron kinetic energy ~30 eV
- maximum photoelectron kinetic energy ~1300 eV (HV power supply limited)
- 2D detector saturation: 106 counts/sec

NEXAFS
- partial electron yield detection with channeltron with grid bias
- free surface orientation with respect to electric field from p to s polarization
  (by sample rotation around the beam axis at constant grazing angle)
- high flux at the Carbon edge (average reduction by 50%)
- simultaneous NEXAFS acquisition during Resonant XPS for energy calibration
LIMITS: no drain current (total yield) measurements

Structural measurements @ ALOISA

PED
- angular PED made by simultaneous rotation of the sample azimuth and the spectrometer polar angle at constant grazing incidence
- mapping emission with constant solid angle steps (reduced oversampling at normal emission)
- best suited for poorly ordered systems
LIMITS: long deadtime due to rotation of the spectrometer (from 6 to 10 hours for a 90-120˚ azimuthal range)

SXRD
- out of plane diffraction (rod scans) at 7 keV
- UHV mounted photodiode allows scanning up to the surface normal (no Be window)
- radial scans by photon energy scans (3 to 8 keV)
- Best suited to study the displacement of surface atoms upon overlayer deposition
LIMITS:
- asymmetric exit slits with fixed width (~0.1˚x0.9˚) limits δh resolution → max 4-5 layer thick films
- photodiode orientation by rotation of experimental chamber and bimodal frame increases deadtime with respect to conventional diffractometers (up to 2 order of magnitudes) → best suited for measurement of surface structure modification rather than crystalline structure determination (no conventional multistacked semiconductors and oxide samples)
 

Ultima modifica il Lunedì, 12 Gennaio 2015 14:43