Self-diffusion of the atomic constituents in the solid state was a fundamental transport process that controlled various materials properties. With established methods of diffusivity determination it was only possible to measure diffusion processes on a length scale down to 10nm at corresponding diffusivities of 10−23m2/s. However, for complex materials like amorphous or nano-structured solids the given values were often not sufficient for a proper characterization. Consequently, it was necessary to detect diffusion length well below 1nm. Here, the method of neutron reflectometry on isotope multilayers was presented. For two model systems, an amorphous semiconductor and an amorphous metallic alloy, the efficiency of this method was demonstrated to detect minimum diffusion lengths of only 0.6 to 0.7nm. It was further shown that diffusivities could be derived which were more than two orders of magnitude lower than those obtainable with conventional methods. Prospects of this method in order to solve actual kinetic problems in materials science were given.

How to Measure Atomic Diffusion Processes in the Sub-Nanometer Range. H.Schmidt, M.Gupta, T.Gutberlet, J.Stahn, M.Bruns: Acta Materialia, 2008, 56[3], 464-70