Sequential sputter deposition of amorphous 4‐nm‐thick Ta and 7‐nm‐thick Si layers leads to the formation of a periodic multilayer that can be regarded as a synthetic one‐dimensional crystal. A simple kinematical diffraction model is presented to discuss x‐ray diffraction patterns obtained from the multilayer structure during annealing. Post‐deposition annealing up to temperatures above 530 °C, where the lattice structure disappears, leads to Si diffusion into the Ta layers forming a nonstoichiometric Ta‐Si phase. The high diffusion rate of Si in Ta leads to a homogeneous distribution of Si in the Ta (silicide) regimes. As shown by cross‐sectional transmission electron microscopy, the interfaces remain sharp during the interdiffusion process. This makes the observation of low‐angle Bragg reflections up to the 12th order possible. The local atomic structure around the Ta atoms was analyzed by measuring the extended x‐ray‐absorption fine structure above the TaLIIIedge at different probing depth conditions. During annealing the local Ta environment was found to be TaSi2like, even if only a small portion of the Si has diffused into the Ta layers, and the silicide formation is far from stoichiometry. The formation of a Ta suboxide was detected in the surface region of the top Ta layer.