Intermetallics formation in the Fe/Ti nanometer-scale multilayers magnetron-sputtering deposited on Si(100) substrate during thermal annealing at 623-873 K was investigated by using small and wide angle X-ray diffraction and cross-sectional high-resolution transmission electron microscopy. The Fe/Ti nanometer-scale multilayers were constructed with bilayer thickness of 16.2 nm and the sublayer thickness ratio of 1:1. At the annealing temperature of 623 K, intermetallics FeTi were formed by nucleation at the triple joins of alpha-Fe(Ti)/alpha-Ti interface and alpha-Ti grain boundary with an orientational correlation of FeTi(110)//alpha-Ti(100) and FeTi[001]//alpha-Ti[001] to adjacent alpha-Ti grains. The lateral growth of intermetallics FeTi which is dependent on the diffusion path of Ti led to a coalescence into an intermetallic layer. With an increase in the annealing temperature, intermetallics Fe(2)Ti were formed between the intermetallics FeTi and the excess Fe due to the limitation of Fe and Ti atomic concentrations, resulting in the coexistence of intermetallics FeTi and Fe(2)Ti. It was found that the low energy interface as well as the dominant diffusion path constrained the nucleation and growth of intermetallics during interfacial reaction in the nanometer-scale metallic multilayers. (C) 2009 Elsevier B.V. All rights reserved.