Self-diffusion and defect annihilation in nanocrystalline Fe films probed by neutron reflectometry

Nanoscale diffusion in Pt/56Fe/57Fe thin-film system

“…This would mean that the effective diffusion coefficients correspond to bulk diffusion. As we will see below these investigations [4,5], although provided very interesting results, raised also questions related to the surprisingly low activation energy and time dependence of the effective diffusion coefficients. Thus, in this communication, on the basis of experiments carried out by depth profiling on 56 Fe/ 57 Fe thin films, we provide a simple model for the interpretation of the time dependence of the effective diffusion coefficients obtained at fixed temperatures.…”

“…More recently publications on diffusion in isotope bi-or multilayered systems indicated that it is possible to investigate, with the use of sophisticated techniques like neutron reflectivity in isotope multilayers [4] or nuclear resonant scattering of synchrotron radiation [5], diffusion intermixing even on bulk diffusion lengths in the order of 0.5-1 nm. At these penetration distances, in epitaxial structures or in stable nanostructures with grain sizes several times larger than the bulk penetration distance, it would be expected the grain boundary contributions can be excluded.…”

“…4 that Fe self-diffusion can be investigated in 57 Fe(7 nm)/ nat Fe(3 nm) 15 multilayers at low temperatures using neutron reflectivity experiments.…”

“…al. [4] argued that they could diminish the grain boundary contributions since no significant grain growth during heat treatments was observed. It was concluded that, according to the Harrison's classification [17], B-type diffusion regime was implemented in which both the bulk and grain-boundary diffusion contribute to the intermixing.…”

“…al. [4] concluded that due to the small bulk diffusion lengths ( 1 nm), the role of grain boundaries could be neglected and point defect annealing processes at around the initial interfaces can explain the observed time dependence of the effective diffusion coefficient. Fe isotope bilayer using depth profiling by a Secondary Neutral Mass Spectrometer (SNMS), which provides a very good depth resolution and even about 1-2 nm [19][20][21][22] can be reached.…”