Positron Spectroscopy Laboratory ELI-NP

The positron spectroscopy laboratory is located in the ERA2 room of the experimental building. Positron Annihilation Lifetime Spectroscopy (PALS), Doppler Broadening Spectroscopy (DBS), and Coincidence Doppler Broadening Spectroscopy (CDBS) are available for performing studies with 48V as a source of fast positrons. DBS, CDBS, and PALS are also available for conducting experiments with a beam of slow positrons of variable energy up to 30 keV.
Additionally, the laboratory is equipped with a photo- and Auger electron spectroscopy system for studying the surface chemistry of a material and the electronic state of the elements within a material.

Main Activities

Positron spectroscopy measurements of solid state materials by CDBS, DBS, and PALS using source of fast positrons. Study of the defect structure, micro- and nano-porosity.
Positron spectroscopy measurements with an intense beam of slow positrons. Depth profiles by DBS.
Surface analysis conducted using X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy.

Equipment

An intense beam of slow positrons obtained by solid Neon moderation with a cryocooler
Magnetic guidance transport beamlines equipped with a steering coil system
Beam monitor units with imaging MCP detectors and 3, 5, and 8 mm apertures for selectable beam spot sizes
Vacuum pumps and gauges
Ultrasonic bath for cleaning of components to be used in UHV
Chamber for heating up to 2500 ºC by electron bombardment
CDBS/DBS sample end-station equipped with a 30 kV accelerator
PALS sample end-station with a 30 kV accelerator
HPGe detectors for performing CDBS and DBS measurements
Fast scintillator (BaF2) detectors for PALS measurements
Load lock chambers for the sample end-stations
Digitizers for the DAQ of the signals from HPGe and scintillator detectors
Photo- and Auger electron spectroscopy system for surface studies
Access to TR19 cyclotron for the production of 48V sources for conventional positron spectroscopy with fast positrons
Software for remote slow control and DAQ

Topics

Study of the defect structure, micro- and nano-porosity of various bulk materials by fast positrons
Examination of the defect structure, micro- and nano-porosity in the subsurface layer of various materials, up to a few microns, using an intense beam of slow positrons with controllable energy
Surface investigation through photoelectron spectroscopy of advanced multifunctional materials, nanomaterials, and nanostructures, aimed at developing devices for industrial applications

Spectrometer specifications and requirements

Coincidence Doppler-Broadening Spectrometer (CDBS)

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

Positron Annihilation Lifetime Spectrometer (PALS)

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: < 300 ps (fwhm)
  • spectrum time range: 25 ns
  • 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
  • measurement can be performed in air or in vacuum and also at elevated temperatures up to 1000º C since 48V source is used.

X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) system

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

Photo Gallery

Positron focusing lens for PAES

Positron focusing lens for PAES

Power supplies

Power supplies

PALS pulsing line

PALS pulsing line

Slow & DAQ Control

Slow & DAQ Control

General view

General view

XPS & AES & PAES

XPS & AES & PAES

Source of slow positrons

Source of slow positrons

CDBS chamber

CDBS chamber

Sample exchange

Sample exchange

Sample exchange

Sample exchange

Sample manipulation in XPS

Sample manipulation in XPS

Sample conditioning in XPS

Sample conditioning in XPS

Team

Name Position Info
Nikolay DJOURELOV Senior Researcher CV     Info
Andreea Bianca ȘERBAN Postdoctoral Fellow, PhD Info
Andrei COVALI Engineer


Former group members

Andreea OPRIȘA
Doru DINESCU
Cosmina NEDELCU

Application procedure for measurements

Potential applicants for laboratory beam time should provide the following information:

  • Description of the sample types (this can include not only one series, but a set of series of samples).
  • Explanation of why it is worth studying the described samples.
  • An overview of the spectroscopy methods available in the laboratory that can be applied to the samples.
  • Expectations for scientific output from the analysis using the chosen spectroscopy method.
Information on measurement conditions or preliminary treatment that should be applied to the samples. The request form in free text should not exceed 1 page and will be considered by a local program committee.

Publications, Abstracts, and Conference Presentations

Contact Us

Secretary

office.sdeli-np.ro