Positron-trapping mechanism at dislocations in Zn

Abstract

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Effect of thermal treatment condition on the Ag precipitates in Al–Ag alloy studied by positron annihilation

“…They are more effective at low temperatures due to small positron binding energy (< 100 meV) and thus the positron wave function is weakly localized, while at higher temperature, positrons can get detrapped from these sites. A number of temperature dependence investigations have been performed on pure metals and alloys, and the observed temperature dependence phenomena were attributed to the escaping of positron from shallow traps via thermal processes [26,[28][29][30]. It is generally accepted that grain boundaries and dislocations in metals can act as shallow traps.…”

Study of Interaction Mechanism between Positrons and Ag Clusters in Dilute Al–Ag Alloys at Low Temperature

“…We attempted to quantitatively describe the positron trapping mechanism in Al-Ag alloys at varied temperatures utilizing the three state trapping model [20,33]. At 15-200 K, there were two positron trapping states in the Al-Ag alloy: free annihilation (bulk state) and deep trapping (Ag-V complex).…”

“…One is the deep positron trapping sites, such as vacancies and voidssince the positron affinity of these defects is less than −1 eV [19], positrons encounter a deep potential well from which it is thereby difficult to escape; the other type is the shallow positron trapping sites-e.g., dislocations. The positron affinities of these defects are greater than −100 meV [20]. Hidalgo et al [21] studied positron annihilation in deformed copper and found that dislocations can also trap positrons, and the positron trapping rate increased when the temperature was below 77 K. In addition to the two above-mentioned typical types of positron trapping sites, in recent years, some clusters have been shown to be able to act as shallow positron trapping sites; e.g., in 2002, Huis et.al [22] found that lithium nanoclusters are able to trap positrons in MgO, and the trapping ability is enhanced at low temperatures.…”

A model for interpreting the positron annihilation characteristics of deformed metals; application to vanadium

“…metals and alloys are determined by the dislocation lines. In contrast there exist other experimental results indicating that the observed positron lifetimes for deformed metals are due to positrons trapped at defects associated with dislocations rather than to positrons annihilating at the dislocation core [5][6][7][8]. Calculations using molecular dynamics simulation and density functional theory support the latter interpretation [9,10].…”