scholarly journals On the Limitations of Positron Annihilation Spectroscopy in the Investigation of Ion-Implanted FeCr Samples

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1689
Author(s):  
Vladimir Slugen ◽  
Jarmila Degmova ◽  
Stanislav Sojak ◽  
Martin Petriska ◽  
Pavol Noga ◽  
...  
Keyword(s):  
Ion Implantation ◽  
Positron Annihilation ◽  
Neutron Irradiation ◽  
Surface Region ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Radiation Embrittlement ◽  
Nuclear Facilities ◽  
Near Surface ◽  
Slow Positron

New materials for advanced fission/fusion nuclear facilities must inevitably demonstrate resistance to radiation embrittlement. Thermal and radiation ageing accompanied by stress corrosion cracking are dominant effects that limit the operational condition and safe lifetime of the newest nuclear facilities. To study these phenomena and improve the current understanding of various aspects of radiation embrittlement, ion bombardment experiments are widely used as a surrogate for neutron irradiation. While avoiding the induced activity, typical for neutron-irradiated samples, is a clear benefit of the ion implantation, the shallow near-surface region of the modified materials may be a complication to the post-irradiation examination (PIE). However, microstructural defects induced by ion implantation can be effectively investigated using various spectroscopic techniques, including slow-positron beam spectroscopy. This method, typically represented by techniques of positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy, enables a unique depth-profile characterisation of the near-surface region affected by ion bombardment or corrosion degradation. One of the best slow-positron beam facilities is available at the pulsed low-energy positron system (PLEPS), operated at FRM-II reactor in Munich (Germany). Bulk studies (such as high energy ion implantation or neutron irradiation experiments) can be, on the other hand, effectively performed using radioisotope positron sources. In this paper, we outline some basics of the two approaches and provide some recommendations to improve the validity of the positron annihilation spectroscopy (PAS) data obtained on ion-irradiated samples using a conventional 22Na positron source.

scholarly journals Study of Microvoids in High-Rate a-Si:H Using Positron Annihilation

1997 ◽  
Vol 467 ◽  
Author(s):  
X. Zou ◽  
D. P. Webb ◽  
S. H. Lin ◽  
Y. W. Lam ◽  
Y. C. Chan ◽  
...  
Keyword(s):  
Thin Films ◽  
Positron Annihilation ◽  
Surface Region ◽  
Positron Beam ◽  
High Rate ◽  
Doppler Broadening ◽  
Slow Positron ◽  
Depth Profiles ◽  
Vacancy Type Defect ◽  
Low Rate

ABSTRACTIn this paper, we have carried out the positron annihilation measurement on high-rate and low-rate a-Si:H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. We have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.

Positron spectroscopy of bulk and near-surface defects in semiconductors

1989 ◽  
Vol 67 (8) ◽  
pp. 813-817
Author(s):  
P. Hautojārvi
Keyword(s):  
Positron Annihilation ◽  
Positron Lifetime ◽  
Surface Defects ◽  
Positron Beam ◽  
Near Surface ◽  
Slow Positron ◽  
Positron Spectroscopy ◽  
Positron Lifetime Spectroscopy ◽  
Defects In Semiconductors ◽  
Ion Implanted

The use of positron annihilation to study defects in semiconductors is discussed. Positron-lifetime spectroscopy reveals As vacancies in as-grown GaAs and gives information on ionization levels. The vacancy profiles in ion-implanted Si are investigated by slow positron beam.

scholarly journals Development of Positron Microbeam in AIST

2008 ◽  
Vol 607 ◽  
pp. 238-242 ◽  
Author(s):  
Nagayasu Oshima ◽  
Ryoichi Suzuki ◽  
Toshiyuki Ohdaira ◽  
Atsushi Kinomura ◽  
T. Narumi ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Spatial Resolution ◽  
Transport System ◽  
Linear Accelerator ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Beam Size ◽  
Electron Linear Accelerator ◽  
Slow Positron ◽  
Magnetic Transport

To improve the spatial resolution of positron annihilation spectroscopy (PAS), a system to produce an intense positron microbeam was developed in AIST. A slow positron beam, which was produced by an electron linear accelerator, was focused by a lens onto a remoderator to enhance its brightness. The brightness-enhanced beam with an intensity of ≈1 × 106 e+/s was extracted from the remoderator and focused onto the sample by a lens. The beam size at the sample was 25 μm, which is more than two and half orders of magnitude smaller than that in the magnetic transport system (≈10 mm). Hence, the spatial resolution of PAS with an AIST positron microbeam can be drastically improved relative to PAS using conventional methods.

Slow positron annihilation studies of vacancy-type defects in the near-surface region of Cu and Nb before and after wear

1999 ◽  
Vol 68 (3) ◽  
pp. 325-327
Author(s):  
H.D. Gu ◽  
T.M. Wang ◽  
W.J. Wang ◽  
K.M. Leung ◽  
C.Y. Chung
Keyword(s):  
Positron Annihilation ◽  
Surface Region ◽  
Near Surface ◽  
Slow Positron ◽  
Before And After

scholarly journals A new approach to near-surface positron annihilation analysis of ion irradiated ferritic alloys

2021 ◽  
Author(s):  
Vladimir Krsjak ◽  
Petr Hruška ◽  
Jarmila Degmova ◽  
Stanislav Sojak ◽  
Pavol Noga ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Ion Beam ◽  
Positron Beam ◽  
Ion Beam Irradiation ◽  
Near Surface ◽  
Slow Positron ◽  
New Approach ◽  
Ferritic Alloys ◽  
Positron Annihilation Lifetime ◽  
Variable Energy

The present work provides an innovative approach to the near-surface slow-positron-beam (SPB) study of structural materials exposed to ion-beam irradiation. This approach enables the use of variable-energy positron annihilation lifetime...

Diffusion Processes in the Sintering of Zirconia-Based Nanomaterials

2013 ◽  
Vol 26 ◽  
pp. 25-31
Author(s):  
Oksana Melikhova ◽  
Jakub Čížek ◽  
Ivan Procházka ◽  
Wolfgang Anwand ◽  
Tetyana E. Konstantinova ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Elevated Temperatures ◽  
Diffusion Processes ◽  
High Sensitivity ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Atomic Scale ◽  
Slow Positron ◽  
Co Precipitation ◽  
Non Destructive

In the present work, zirconia-based nanomaterials with various stabilizers were prepared by a co-precipitation technique. Defects in these nanomaterials were characterized by positron annihilation spectroscopy which is a non-destructive technique with a high sensitivity to open volume defects and atomic scale resolution. It was found that zirconia-based nanomaterials contain vacancies and also nanoscale and meso-scale pores. Diffusion processes which occur in the nanomaterials sintered at elevated temperatures were investigated by depth sensitive positron annihilation studies on a variable energy slow positron beam. It was found that sintering causes intensive grain growth and residual porosity is removed from samples by diffusion to the surface.

scholarly journals Microscopy studies on magnetron sputtered thin films with preferred orientation for positron moderation

2019 ◽  
Vol 1 (1) ◽  
pp. 62-63
Keyword(s):  
Thin Films ◽  
Positron Annihilation ◽  
Branching Ratio ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Structure Characterization ◽  
Near Surface ◽  
Positron Annihilation Lifetime ◽  
Pass Through ◽  
Intrinsic Characteristic

Doppler-broadening Spectroscopy (DBS) and positron annihilation lifetime spectroscopy (PALS) are two positron annihilation spectroscopy techniques used for identifying near surface vacancies and lattice dislocations. Positrons manifest a broad energy distribution of about several MeV and in order to generate a low-energy positron beam, the positrons need to pass through a material called “moderator” so that a narrow positron kinetic energy bandwidth can be obtained, without losing too much intensity. The moderator must possess certain properties, among which a large negative positron work function and a large branching ratio to free positrons. The first can be assessed to an intrinsic characteristic of the material, that is usually correlated to the material bandgap, and in order to attain the second, a defect free, epitaxial thin film should be obtained. Due to its 3.4 eV bandgap, GaN represents a very promising candidate for positron moderation and field assisted moderation, that might manage longer average positron diffusion lengths. The aim of the present study is to obtain semi-insulating GaN thin films by magnetron sputtering GaN on different substrates (ZnO, TiO2, Al2O3) with fewer impurities incorporated, which should hold promises of increasing the positron diffusion length in the material. Preliminary depositions made in this study are to be discussed, highlighting both their advantages and limitations derived from their structure characterization.

Positron Annihilation Spectroscopy at LEPTA Facility

2012 ◽  
Vol 733 ◽  
pp. 322-325 ◽  
Author(s):  
Aleksey A. Sidorin ◽  
Igor Meshkov ◽  
E. Ahmanova ◽  
M. Eseev ◽  
A. Kobets ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Condensed Matter ◽  
Positron Beam ◽  
Positron Annihilation Spectroscopy ◽  
Layered Structures ◽  
Low Energy ◽  
Slow Positron ◽  
Monochromatic Beam

The Low Energy Positron Toroidal Accumulator (LEPTA) at JINR proposed for generation of positronium in flight can be used for positron annihilation spectroscopy (PAS) [1]. The positron injector of the LEPTA facility can generate continuous a slow positron beam with the intensity up to 1∙107s-1 at the energy in the range of a few eV to 100 keV and width of the spectrum 1 – 2 eV. The injector is based on radioactive 22Na isotope. The solid neon is used as a moderator to generate monochromatic beam. The parameters of the positron beam allow scanning the condensed matter in depth up to 10 microns with resolutions less than 10 nanometers and investigating layered structures for microelectronics and properties of a surface.

Application of Positron Annihilation Spectroscopy to the Study of Irradiated Fe-Cr Alloys

2012 ◽  
Vol 331 ◽  
pp. 165-179 ◽  
Author(s):  
Maik Butterling ◽  
Frank Bergner ◽  
Cornelia Heintze ◽  
Wolfgang Anwand ◽  
Andreas Ulbricht
Keyword(s):  
Ion Implantation ◽  
Positron Annihilation ◽  
Neutron Irradiation ◽  
Early Stage ◽  
Positron Annihilation Spectroscopy ◽  
Cr Content ◽  
Induced Defects ◽  
Irradiation Induced Defects

The aim of this work was to investigate the effect of Cr on the microstructure of neutron-irradiated Fe-Cr alloys. Neutron irradiation-induced damage at its early stage was simulated by ion implantation. Positron Annihilation Spectroscopy was applied to identify irradiation-induced defects depending on the Cr-content in Fe-Cr alloys. Different irradiation scenarios were used to investigate the influences of irradiation step by step.

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