We present a low temperature diffusion study on the formation of intermixing zones between periodic, nanometer thick films consisting of Mo and Si. An in-situ X-ray diffraction method at pm-accuracy was developed, including a model that explains the period change observed by diffusion limited interface growth. Experiments were carried out on Mo/Si multilayered films in the temperature range of 100-275 degrees C, resulting in the determination of diffusion coefficients. Temperature scaling showed Arrhenius-type behavior of the diffusion constant over the entire temperature range, with an activation energy of 0.5 eV. (C) 2010 Elsevier B.V. All rights reserved.