Positrons in Imperfect Solids: Theory

Nieminen, Risto M.; Manninen, M.

doi:10.1007/978-3-642-81316-0_4

Cited by 48 publications

(30 citation statements)

References 139 publications

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“…Such assertion can be deduced from the experimental results and ab-initio calculations of positron lifetimes obtained in similar materials. From the experimental point of view, it is well-known that positron lifetime in pure well-annealed Mg is above of 230 ps [7]. This value is in excellent agreement with that obtained by ab-initio calculations (details are given in Ref.…”

supporting

confidence: 84%

Age‐hardening in a commercial Mg‐based alloy

Macchi

Somoza

Nie

2007

Phys. Status Solidi (c)

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Age-hardening phenomena induced by thermal and thermo-mechanical treatments in the commercial Mgbased alloy WE54 were studied by positron annihilation lifetime spectroscopy and Vickers microhardness. To this aim, samples were plastically deformed and subsequently aged at 250 °C for times ranging from 0 to 1000 hours. The results obtained are discussed in terms of the role of vacancies in the solute transport and therefore they contribute to the discussion on the vacancy-solute clusters (and/or intermediate precipitates) interactions during the precipitation sequence of the WE54. Besides, we show that cold work previous aging not only accelerates but increases the hardening response of the alloy.

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supporting

confidence: 84%

Age‐hardening in a commercial Mg‐based alloy

Macchi

Somoza

Nie

2007

Phys. Status Solidi (c)

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“…For the metals the acoustic longitudinal phonon scattering dominates, and its contribution can be calculated using the deformation-potential approximation (Bardeen and Shockley, 1950) The decomposition of the positron lifetime spectrum is explained by the trapping model (Bertolaccini et al , 1971;Brandt, 1974) (West, 1979) 1. It is generally accepted that the trapping coe%cients for vacancies in metals are of the order of 10' -10' s (Nieminen and Manninen, 1979;West, 1979 Hodges (1970).…”

Section: Fig 4 Transmission Probabilities For Positrons and Electronsmentioning

confidence: 99%

“…The aim of this review is to update the series of earlier general summaries of positron theory (Nieminen and Manninen, 1979;Nieminen, 1983},which (a) vacancy in fcc Ni; (b) vacancy in Si with diamond structure; (c) divacancy in Si. The calculations were performed using the superimposed-atom method (Puska and Nieminen, 1983a).…”

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confidence: 99%

Theory of positrons in solids and on solid surfaces

1994

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Various experimental methods based on positron annihilation have evolved into important tools for researching the structure and properties of condensed matter. In particular, positron techniques are useful for the investigation of defects in solids and for the investigation of solid surfaces. Experimental methods need a comprehensive theory for a deep, quantitative understanding of the results. In the case of positron annihilation, the relevant theory includes models needed to describe the positron states as well as the different interaction processes in matter. In this review the present status of the theory of positrons in solids and on solid surfaces is given. The review consists of three main parts describing (a) the interaction processes, {b) the theory and methods for calculating positron states, and {c)selected recent results of positron studies of condensed matter. CONTENTS

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“…It should, however, be noted that the binding energy of a positron in a Li monovacancy is too low to cause trapping. [49][50][51] Neither positron lifetime nor 1D-ACAR measurements in the alkali metals have indicated evidence of trapping by vacancies. 52,53 Future investigations including measurements at low temperature to reduce the thermal generation of vacancies are necessary to accurately quantify the fraction of annihilations in Li vacancies and to identify the type of vacancies.…”

Section: Discussionmentioning

confidence: 99%

Electronic structure and orientation relationship of Li nanoclusters embedded in MgO studied by depth-selective positron annihilation two-dimensional angular correlation

et al. 2002

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Quantum-confined positrons are sensitive probes for determining the electronic structure of nanoclusters embedded in materials. In this work, a depth-selective positron annihilation 2D-ACAR ͑two-dimensional angular correlation of annihilation radiation͒ method is used to determine the electronic structure of Li nanoclusters formed by implantation of 10 16 -cm Ϫ2 30-keV 6 Li ions in MgO ͑100͒ and ͑110͒ crystals and by subsequent annealing at 950 K. Owing to the difference between the positron affinities of lithium and MgO, the Li nanoclusters act as quantum dots for positrons. 2D-ACAR distributions for different projections reveal a semicoherent fitting of the embedded metallic Li nanoclusters to the host MgO lattice. Ab initio KorringaKohn-Rostoker calculations of the momentum density show that the anisotropies of the experimental distributions are consistent with an fcc crystal structure of the Li nanoclusters. The observed reduction of the width of the experimental 2D-ACAR distribution is attributed to positron trapping in vacancies associated with Li clusters. This work proposes a method for studying the electronic structure of metallic quantum dots embedded in an insulating material.

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Positrons in Imperfect Solids: Theory

Cited by 48 publications

References 139 publications

Age‐hardening in a commercial Mg‐based alloy

Age‐hardening in a commercial Mg‐based alloy

Theory of positrons in solids and on solid surfaces

Electronic structure and orientation relationship of Li nanoclusters embedded in MgO studied by depth-selective positron annihilation two-dimensional angular correlation

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