Temperature dependence of the source component in positron annihilation measurements

MacKenzie, I. K.; Fabian, Jaroslav

doi:10.1007/bf02899885

Cited by 13 publications

(12 citation statements)

References 10 publications

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“…These results provide clear evidence for a dominant single positron lifetime component with a value of 385(1) ps in Kapton HN for both foil thickness studied. This is in agreement with the early bulk PALS reports of a single lifetime value of 382 ps [16], and 382(3) ps [10], and with the most recent study giving 385(3) ps [13]. The measurements provide further evidence that previously reported two component fits result from an artefact of the fitting process [11,12,14].…”

Section: Resultssupporting

confidence: 92%

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Positron annihilation lifetime spectroscopy study of Kapton thin foils

Kanda

Ravelli

Löwe

et al. 2015

J. Phys. D: Appl. Phys.

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Variable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.

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Section: Resultssupporting

confidence: 92%

“…The adoption of Kapton foils for use in PALS followed a study by MacKenzie and Fabian [16], that reported a single lifetime component of 382 ps and a weak temperature dependence. Subsequently studies on stacked Kapton foils reported lifetime values of 386(7) ps [9], and of 382(3) ps [10].…”

Section: Introductionmentioning

confidence: 99%

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Kanda

Ravelli

Löwe

et al. 2015

J. Phys. D: Appl. Phys.

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“…Indeed, recent works demonstrate the existence of positron surface states on topological insulators [56]. The second lifetime component is related with the positron annihilation in Kapton, which is 382 ps [57,58]. The calculated intensity [59] for the positrons annihilating in Kapton has been 25%, whereas the experimentally obtained value of the intensity that minimizes the χ 2 in the spectra has been 24.5%.…”

Section: Experimental Methodsmentioning

confidence: 90%

Observation of a charge delocalization from Se vacancies inBi2Se3: A positron annihilation study of native defects

et al. 2016

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By means of positron annihilation lifetime spectroscopy, we have investigated the native defects present in Bi 2 Se 3 , which belongs to the family of topological insulators. We experimentally demonstrate that selenium vacancy defects (V Se1 ) are present in Bi 2 Se 3 as-grown samples, and that their charge is delocalized as temperature increases. At least from 100 K up to room temperature both V 0Se1 and V + Se1 charge states coexist. The observed charge delocalization determines the contribution of V Se1 defects to the n-type conductivity of Bi 2 Se 3 . These findings are supported by theoretical calculations, which show that vacancies of nonequivalent Se1 and Se2 selenium atoms are clearly differentiated by positron annihilation lifetime spectroscopy, enabling us to directly detect and quantify the most favorable type of selenium vacancy. In addition to open-volume defects, experimental data indicate the presence of defects that act as shallow traps, suggesting that more than one type of native defects coexist in Bi 2 Se 3 . As will be discussed, the presence of a dislocation density around 10 10 cm −2 could be the source of the detected shallow traps. Understanding the one-dimensional defects and the origin of the charge delocalization that leads Bi 2 Se 3 to be an n-type semiconductor will help in the development of high-quality topological insulators based on this material.

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“…The positron source, 22 Na from a carrier free neutral solution, was deposited between two identical 7.5 µm ®Kapton foils (in which positronium is not formed ), glued together and inserted in the specimen to be studied in the usual sandwich configuration. Care was taken to prevent the glue from reaching the region involved in annihilation.…”

Section: Methodsmentioning

confidence: 99%

Thermomechanical and large deformation behaviors of antiplasticized epoxy resins: Effect of material formulation and network architecture

Pandini

Bignotti

Baldi

et al. 2017

Polymer Engineering & Sci

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A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric ratio and the relative amounts of diepoxide and monoepoxide resin to chemically control the material composition and macromolecular architecture (chain segments flexibility; crosslink density; amounts of dangling groups). Positron Annihilation Lifetime Spectroscopy was used to investigate the free volume associated to the various epoxy formulations, while dynamic-mechanical analysis was employed to investigate their network density and their primary and secondary mechanical relaxations. The mechanical behavior at small and large strain was studied by means of tensile and compression tests. The results pointed out that deviations from the ideal stoichiometric composition and the addition of monoepoxide resins lead to significant room temperature stiffening, together with a reduction of the crosslink density and glass transition temperature. This behavior, phenomenologically associated to antiplasticization, was interpreted according to the specific macromolecular architecture and ascribed to chain mobility hindrance, as revealed by secondary transitions, whereas no significant contribution from the free volume could be evidenced. Furthermore, it was shown that depending on the strain scale and on the corresponding deformational mechanisms, the mechanical response may be differently influenced either by the presence of dangling groups or by the network density

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Temperature dependence of the source component in positron annihilation measurements

Cited by 13 publications

References 10 publications

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Positron annihilation lifetime spectroscopy study of Kapton thin foils

Observation of a charge delocalization from Se vacancies inBi2Se3: A positron annihilation study of native defects

Thermomechanical and large deformation behaviors of antiplasticized epoxy resins: Effect of material formulation and network architecture

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