Positron Annihilation Spectroscopy of As Vacancies in As-Grown GaAs

1987 ◽  
Vol 104 ◽  
Author(s):  
C. Corbel ◽  
M. Stucky ◽  
P. Hautojärvi ◽  
K. Saarinen ◽  
P. Moser
Keyword(s):  
Fermi Level ◽  
Positron Annihilation ◽  
Conduction Band ◽  
Direct Evidence ◽  
Positron Lifetime ◽  
Positron Annihilation Spectroscopy ◽  
Lifetime Measurements ◽  
Positron Trapping ◽  
P Type

ABSTRACTPositron lifetime measurements give direct evidence on positron trapping in monovacancy defects in n-type, but not in p-type nor in semi-insulating LEC-grown GaAs. The defects are identified as As vacancies. Two Fermi level controlled transitions have been found in positron lifetime spectra at 0.03±0.01 eV and at 0.10±0.01 eV below the conduction band. We attribute them to the 2-/- and - / 0 ionisation levels of the As vacancy.

scholarly journals Direct evidence of impurity decoration of Ga vacancies inGaNfrom positron annihilation spectroscopy

2006 ◽  
Vol 73 (19) ◽  
Author(s):  
S. Hautakangas ◽  
I. Makkonen ◽  
V. Ranki ◽  
M. J. Puska ◽  
K. Saarinen ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Direct Evidence ◽  
Positron Annihilation Spectroscopy

Positron Annihilation Lifetime Measurements in Collagen Biopolymer

1998 ◽  
Vol 530 ◽  
Author(s):  
S. Siles ◽  
G. Moya ◽  
X.H. Li ◽  
J. Kansy ◽  
P. Moser
Keyword(s):  
Positron Annihilation ◽  
Amorphous Region ◽  
Positron Annihilation Spectroscopy ◽  
Lifetime Data ◽  
Spectroscopy Technique ◽  
Lifetime Measurements ◽  
Lifetime Distributions ◽  
Positron Annihilation Lifetime ◽  
Coincidence System ◽  
Three Components

AbstractLifetime measurement in Positron Annihilation Spectroscopy (PAS) is applied to the study of free-volume collagen characteristics as a function of concentration. The lifetimes of positrons were obtained by a conventional fast-fast coincidence system. All lifetime data are fitted in three components by using the computer program POSITRON FIT and resolved. For each concentration, lifetime distributions were analyzed in order to obtain the different components, thus we have observed three components of which a long component τ3. This long lived component can be associated with a pick-off annihilation of ortho-positronium (o-Ps) trapped in free volumes of amorphous region. This investigation shows the potential of the positron annihilation spectroscopy technique in the study of biopolymer microstructures.

Study of PRIMAVERA steel samples by positron annihilation spectroscopy technique II – Lifetime measurements

2012 ◽  
Vol 421 (1-3) ◽  
pp. 97-103 ◽  
Author(s):  
V. Krsjak ◽  
V. Grafutin ◽  
O. Ilyukhina ◽  
R. Burcl ◽  
A. Ballesteros ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Positron Annihilation Spectroscopy ◽  
Spectroscopy Technique ◽  
Lifetime Measurements

Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation

2012 ◽  
Vol 733 ◽  
pp. 219-223 ◽  
Author(s):  
P.M.G. Nambissan ◽  
O. Mondal ◽  
C. Chakrabarty ◽  
M. Pal
Keyword(s):  
Positron Annihilation ◽  
Spinel Structure ◽  
Positron Lifetime ◽  
Drastic Change ◽  
Doppler Broadening ◽  
Positron Trapping ◽  
Normal Spinel ◽  
Ni Substitution ◽  
Positron Lifetimes ◽  
Coincidence Doppler Broadening

We report in this work about the inversion of the spinel structure of ZnFe2O4induced by the substitution of Zn2+by Ni2+ions. Positron lifetimes were measured in Zn1-xNixFe2O4with different concentrations (x) of doped Ni2+ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni2+is smaller in size than Zn2+, defects due to non-stoichiometry are less in NiFe2O4than in ZnFe2O4. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.

Positron state and Lifetime in C60/C70 Fullerites

1992 ◽  
Vol 270 ◽  
Author(s):  
H.-E. Schaefer ◽  
M. Forster ◽  
R. WÜrschum ◽  
F. Banhart
Keyword(s):  
Electron Microscopy ◽  
Hydrostatic Pressure ◽  
High Resolution ◽  
Positron Annihilation ◽  
Positron Lifetime ◽  
High Resolution Electron Microscopy ◽  
Lattice Defects ◽  
Lifetime Measurements ◽  
Resolution Electron ◽  
Positron State

ABSTRACTThe present paper reports on positron lifetime measurements on Ceo/C 70 fullerite powder as a function of temperature and quasi-hydrostatic pressure in order to give an estimate of the positron annihilation site in the fullerite lattice. A single-component positron lifetime of 402 ps is observed which significantly decreases under quasi-hydrostatic pressure. From this and the soft intermolecular properties of the fullerites one can conclude that the positron is annihilated rather in the intermolecular space than inside the fullerene molecules. However, positron trapping at lattice defects, which are observed by high-resolution electron microscopy, cannot be ruled out.

Defects Distribution of Pr2Fe14B Hard Magnetic Magnet from Amorphous to Nanostructures Characterized by Positron Annihilation Spectroscopy

2005 ◽  
Vol 475-479 ◽  
pp. 2123-2126
Author(s):  
Yu Cheng Wu ◽  
W. Sprengel ◽  
K. Reimann ◽  
K.J. Reichle ◽  
D. Goll ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Grain Growth ◽  
Melt Spinning ◽  
Positron Lifetime ◽  
Positron Annihilation Spectroscopy ◽  
Amorphous Structure ◽  
Defect Distribution ◽  
Positron Lifetime Spectroscopy ◽  
Positron Lifetimes ◽  
Shape And Size

The defect distributions have been investigated using positron lifetime spectroscopy on amorphous and nanocrystalline Pr2Fe14B samples, produced by melt-spinning and nanocrystallization route. The main two components can be concluded that were ascribed to vacancy-like defects in the intergranular layers or the interfaces, and microvoids or large free volumes with size compared to several missing atoms at the interactions of the atomic aggregates or the crystallites. The remarkable changes in the positron lifetimes from the amorphous structure to the nanocrystalline with varied sizes can be interpreted, indicating that the structural transformation and the grain growth induce the defect distribution changes occurring at the interfaces with different shape and size.

scholarly journals POSITRON LIFETIME MEASUREMENTS IN NATURAL RUBBER WITH DIFFERENT FILLERS

2013 ◽  
Vol 22 ◽  
pp. 112-117 ◽  
Author(s):  
A. MANDAL ◽  
S. MUKHERJEE ◽  
S. PAN ◽  
A. SENGUPTA
Keyword(s):  
Natural Rubber ◽  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Amorphous Region ◽  
Filler Concentration ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

Positron annihilation lifetime spectra (PLAS) have been measured for natural rubber polymer with different fillers (Titenium dioxide, Nanosilica and Nanoclay) as a function of filler concentration to investigate how these fillers affect the microstructure of free volume of natural rubber. The lifetime spectra is analyzed by using LT9.0 and the longest lived component(τo-Ps) is attributed to the pick- off annihilation of o-Ps in free volume sites, available mostly in the amorphous region of polymer. On the basis of the τo-Ps values the radii of the free volume holes (Rh) are calculated. The PALS results show that o-Ps lifetime as well as the size of free volume decreases with the increase of filler concentration.

Positron annihilation spectroscopy in doped p-type ZnO

2011 ◽  
Author(s):  
Sayanee Majumdar ◽  
D. Sanyal ◽  
Alka B. Garg ◽  
R. Mittal ◽  
R. Mukhopadhyay
Keyword(s):  
Positron Annihilation ◽  
Positron Annihilation Spectroscopy ◽  
P Type

Positron Lifetime Studies of Polyaniline Conducting Polymers

1995 ◽  
Vol 413 ◽  
Author(s):  
C. M. Huang ◽  
J. Liu ◽  
T. C. Sandreczki ◽  
Y. C. Jean
Keyword(s):  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
The Other ◽  
Chemical Compositions ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime ◽  
Positron Lifetimes ◽  
Lifetime Studies ◽  
Made In

ABSTRACTPositron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.

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