Composition dependence of the nucleation energy of iron antimonides from modulated elemental reactants

Modulated elemental reactants containing iron and antimony were found to re act at low temperature (T < 200 <degrees>C) forming either FeSb2 or FeSb3 d epending on both the layer thicknesses and the overall composition of the i nitial reactant. For films containing 75% antimony and 25% iron, the metast able compound FeSb3 was observed to nucleate and grow if the layer thicknes s was below approximately 35 Angstrom. Above this critical thickness for th e modulation, annealing led to the formation of FeSb2. This, combined with low-angle diffraction data, suggests that the initial interdiffusion betwee n iron and antimony layers in an elementally modulated reactant results in the formation of an amorphous reaction intermediate if the layering thickne ss is less than 35 Angstrom. For modulated reactants with composition betwe en 70 and 90 atomic % antimony and below this critical layer thickness, the metastable compound FeSb3 formed. In more iron-rich modulated reactants Fe Sb2 nucleates. The nucleation temperature and the nucleation energy of FeSb 3 were found to be a function of the composition of the amorphous intermedi ate, while those of FeSb2 were found to be relatively independent of compos ition.