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Ligament coarsening in nanoporous gold: Insights from positron annihilation study
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Image of FIG. 1.
FIG. 1.

Evolution of microstructure of np-Au up on temperature annealing. (a) SEM micrographs of np-Au obtained after annealing at various temperatures 30, 55, 85, 110, 155, 210, 255, and 500 °C for 6 h. Closed pore structure develops in the sample at higher annealing temperatures. (b) Increase in the ligament diameter with annealing temperature. (c) Decrease in the ratio A/A of pore to ligament area with annealing temperature. Beyond 300 °C, the nanoporous morphology changes to a disconnected closed pore structure and densification takes place.

Image of FIG. 2.
FIG. 2.

Positron lifetime spectra in np-Au compared with those in annealed and cold-worked bulk Au. Measurements were carried out under vacuum of ∼10 mbar to avoid the effects of trapped gases in the pores. The spectrums are area normalized.

Image of FIG. 3.
FIG. 3.

Variation of positron lifetime parameters. (a) τ; (b) τ; (c) I; and (d) τ with annealing temperature in np-Au. The right ordinate in panel (c) shows the increase in the ligament diameter with temperature, as obtained from SEM studies. The vertical dotted lines mark the distinctive stages, inferred from positron experiments, corresponding to the migration of vacancies at 85 °C, instability at the surface of ligaments at ∼175 °C and the transition to closed pore structures at ∼500 °C.


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Table I.

Positron annihilation lifetime parameters, τ, τ, I, I for as-dealloyed np-Au, compared with reference samples of master alloy AgAu used for the dealloying and cold worked and annealed bulk Au. The bulk Au and AgAu samples were annealed, respectively, at 850 °C and 700 °C in vacuum better than 10 mbar and subjected to air cooling to obtain nearly defect free samples.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Ligament coarsening in nanoporous gold: Insights from positron annihilation study