A Coincidence Doppler Broadening Spectrometer (CDBS) and its simpler version, Doppler Broadening Spectrometer (DBS),
are available for experiments. For the CDBS, two couples of two HPGe detectors, facing each other, are used to detect
annihilation 𝛾-rays in time and energy condition coincidence. Electron momentum distributions extracted from CDBS
spectra carry information on the chemical surrounding of the e+ annihilation sites, extremely valuable
for identifying the type of defects in metals and semiconductors. For the DBS, the detectors operate independently.
- HPGe detectors efficiency: 25%, resolution: ~1.3 keV (fwhm) @ 511 keV
- slow positron energy range: 0.2 -30 keV, i.e. depth profiling to depths of up to few µm.
- sample size for beam measurements: max: 14.5×14.5 mm2, thickness 3 mm, min: ø5 mm
- sample size for measurements with fast positrons: 2 samples of each type, minimum thickness calculated in
mm is 1.7/ρ(g/cm3); min size is ø6 mm, note that 1 sample of type and thinner samples are possible to be
measured but with enhanced uncertainty
- min. acquisition time for DBS spectrum at a fixed e+ energy: 8 min
- min. acquisition time for CDBS spectrum at a fixed e+ energy: 400 min
- typical type to load into the load lock a set of 10 samples: 30 min
- typical time to exchange a sample for measurement < 1 min
A Positron Annihilation Lifetime Spectroscopy (PALS) with slow e+ is under construction.
A pulsed section of the e+ beam has been designed. The e+ pulses will arrive at the target with
a time spread of about 100 ps (fwhm). A BaF2 crystal,
coupled to a photomultiplier, will be placed closely behind the sample, and will provide the PALS stop signal.
PALS measurements are particularly powerful for determining the size (type) of open volume defects, as well as
their relative concentrations. Additionally, in a wide range of materials where positronium is formed, PALS is
used as a porosimetry tool sensitive to both open and closed nano- and micro-pores.
The PALS spectrometer with fast positrons is currently operational.
- time resolution with the BaF2 detector: < 250 ps (fwhm)
- sample size for measurements with fast positrons: 2 samples of each type, minimum thickness calculated
in mm is 1.7/ρ(g/cm3); min size is ø6 mm, note that 1 sample of type and thinner samples are possible
to be measured but with enhanced uncertainty
- min. acquisition time for a PALS spectrum is 200 min
- room temperature measurements are performed with a 22Na source
- measurement can be performed in air or in vacuum and also at elevated temperatures up to 600º C since 48V source is used.
The CDBS/DBS is analogous to the CDBS/DBS system with slow positrons. The sample's requirements are the same as for the PALS with fast positrons.
The multi-functional X-ray Photoelectron Spectroscopy (XPS), and electron- and X-ray induced AES setup allows for studies
in a broad temperature range, from 130 K up to 1073 K. It consists of two vacuum chambers: one with double function
- as a load lock and sample cleaning (with an IR heating unit and a sputter gun), and the analysis chamber.
The main components of the analysis chamber are: 150 mm hemispherical analyzer with a 1D detector, dual anode
Al/Mg X-ray source, electron gun for AES studies, a flood gun, a sample stage with 4-axis manipulator, and a MCP detector.
The instrument is coupled to the positron beam line by termination of the guiding magnetic field and by applying an
electrostatic focusing of the e+ on the target. Positron annihilation induced AES (PAES) upgrade is under
construction.
The XPS and AES techniques are fully functional with the following specifications:
- analysis chamber vacuum: < 1×10-9 mbar
- X-ray source: dual Al/Mg
- sample size: max 14×12 mm2 with thickness ≤ 3 mm
- sample temperature: 130 K to 1070 K
- mild Ar etching for surface cleaning
- typical acquisition time for a XPS/AES survey spectrum: 2 min
- typical acquisition time for a XPS/AES high resolution single peak spectrum: 5 min
- typical time to load a sample: 15 min
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