Ultrafast-deposition and a-Si precursor or cap layer are analyzed as possible approaches to the control upon interface intermixing and film growth process. A simple and effective design is delivered providing deposition rates up to 10(4) nm/s. XPS results evidence formation of Fe3Si in the layered structure Fe/a-Si/Si. Cross-section HRTEM data demonstrate enhanced intermixing at the a-Si/Fe film interface. Magnetic properties of the Fe-Si structures grown by the above methods are studied by in situ magneto-optic Kerr effect. Intermixing at the Fe/Si interface is the result of chemical reaction rather than diffusion. (C) 2011 Elsevier B. V. All rights reserved.