MUON DIFFUSION IN NANOCRYSTALLINE COPPER

A systematic mu SR study on nano-Cu has demonstrated that the diffusio n of mu(+) in nanocrystalline metals is influenced by both features of the nanostructure, i.e., by the very small grain size and by the comp aratively large fraction of grain boundaries. The former feature yield s a size effect of the phonon-assisted muon tunneling, but only at par ticle diameters below 20 nm. The latter feature, in samples with cryst allite sizes above 20 nm diameter, i.e., with bulk diffusional behavio ur, establishes a connection between mu(+) diffusion coefficient and p article size: if one of these quantities is known, the other could be evaluated.