Ni nanowries were fabricated by atomic force microscope nanolithography, evaporation, lift-off and annealing processes. Epitaxial NiSi2 nanowires on a Si(100) surface along Si(110) and (100) directions were formed by the rapid thermal annealing treatment of the Ni nanowires at 400 degrees C. The silicide nanowires along the Si(110) direction had coherent type-A Si(111) and Si(100) interfaces, while those along the Si(100) direction had a type-A Si(110) interface. Silicide nanowires were agglomerated when the Ni nanowires were annealed at high temperature (> or = 500 degrees C). The mechanism of formation of a faceted nanowire was discussed based on the minimization of the total surface energy.