PLEPS

Pulsed low energy positron system

PLEPS is a unique tool for depth profiling of defects with positron annihilation lifetime spectroscopy using a pulsed positron beam of variable energy.

Positron lifetime measurements allow the determination of type and size of open volume defects (such as vacancies, vacancy-clusters, dislocations, grain boundaries etc., and free volumes in polymers) in a wide variety of materials and provide information on defect-concentration. In combination with a monoenergetic positron beam of variable energy depth-resolved defect analysis becomes possible.

Typical applications

Defect identification in thin layers and layered structures of semiconductors and insulators
Radiation induced defects in materials for fusion and fission reactors
Characterisation of free volumes in polymers and glasses

Technical Data

Beam properties

Positron implantation energy: 0.5 – 20 keV
Beam spot Ø ~ 1 mm
Count rate: ~ 5000 – 10000 cps

Sample

Limited to 5 × 5 mm² – 9 × 9 mm²

Typical measurement times

< 10 min per spectrum (> 3 · 10⁶ counts in the spectrum)
Depth-profile: 4 – 5 h (15 – 20 implantation energies, > 3 · 10⁶ counts in the spectrum)
Time-window: 20 or 40 ns
Time-resolution: 260 – 280 ps
Peak/ background > 50000 : 1

Instrument Scientist

Dr. Werner Egger
Phone (office TUM): +49 (0)89 289-12299
Phone (office UniBW): +49 (0)89 6004-3507
E-Mail: werner.egger@unibw.de

Operated by

Instrument-DOI

doi:10.17815/jlsrf-1-52

Gallery

PLEPS

Positron lifetime spectrum

Typical positron lifetime spectrum in an epoxy-based industrial adhesive. The positron implantation energy was 18 keV according to a mean implantation depth of 4 µm. The spectrum can be decomposed into three exponentials with three different lifetimes. From the longest lifetime of 2.3 ns the mean size of free volume cavities in the polymer is estimated to be 0.13 nm3.

AMoC spectrum

Age-Momentum Correlated (AMoC) spectrum in Kapton measured with a BaF2 scintillation detector and a HP-Ge detector in coincidence. AMoC measurements contain information about the type of defect and its chemical environment, thus giving a more complete picture of the annihilation site than lifetime measurements and Doppler broadening measurements alone.

PLEPS components

MLZ is a cooperation between:

> Technische Universität München

> Helmholtz-Zentrum Hereon

> Forschungszentrum Jülich

MLZ is a member of:

> LENS

> ERF-AISBL

MLZ on social media: