Nanostructured samples were prepared, via inert-gas condensation and  in situ  vacuum compaction (0.15 to 1.50GPa), and were investigated by means of positron lifetime spectroscopy. The results indicated that there was a common characteristic, in that only 3 lifetime components could be resolved in the lifetime spectrum. Three types of defect (traps) corresponded to the 3 lifetime components. These were: vacancy-like defects, vacancy-cluster defects and larger voids. It was noted that the compaction pressure and annealing treatment had marked effects upon the positron annihilation behavior. The lifetimes and the corresponding intensities decreased irreversibly with compacting pressure and annealing temperature; thus indicating that the defects were mechanically and thermally unstable, and could not be considered to be structural elements of nanostructured Ag. The interfaces in these samples could also be considered to be superpositions of defects on normal ordered boundaries and, since the numbers and sizes of the defects changed with the external conditions, the interfaces could remain in various metastable states. This implied that its interfacial structure could range from totally random states (gas-like) to completely ordered structures; depending upon the numbers and sizes of the associated defects. The formation of bulk nanostructured Ag, as revealed by positron lifetime spectroscopy, could be divided into 3 stages. These were an interface formation stage (compaction pressures of up to 0.6GPa), rapid elimination of the 3 types of defect (0.6 to 1.1GPa) and gradual elimination (above 1.1GPa).

Formation Process of Interfaces and Micro-Defects in Nanostructured Ag Studied by Positron Lifetime Spectroscopy X.Y.Qin, J.S.Zhu, L.D.Zhang, X.Y.Zhou: Journal of Physics - Condensed Matter, 1998, 10[13], 3075-88