It was noted that, when using established methods of diffusivity determination, it was possible to measure diffusion processes only on a length-scale down to 10nm; with corresponding diffusivities of 10-23m2/s. However, in the case of complex materials such as amorphous or nano-structured solids, the above limits were often insufficient to permit proper characterization. It was therefore necessary to detect diffusion lengths which were well below 1nm. Here, the method of neutron reflectometry on isotope multi-layers was presented. For 2 model systems (an amorphous semiconductor and an amorphous metallic alloy), the efficiency of this method was demonstrated by detecting minimum diffusion lengths of only 0.6 to 0.7nm. It was further shown that diffusivities could be derived which were more than 2 orders of magnitude lower than those obtained when using conventional methods.

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