By analogy to reactive deposition epitaxy and titanium interlayer mediated epitaxy experiments, an attempt has been made to constrain the supply of reactants to the reaction interface in the solid phase reaction between Fe and Si. The goal being to change the normal phase formation sequence by using a suitable diffusion barrier, so that β-FeSi2 forms directly. Both Fe-V and Fe-Zr diffusion barriers were used to constrain the supply of the two reactants during Fe-silicide formation. Measurements with these barriers, show first phase formation of β-FeSi2, but direct formation of 3-FeSi2 as first phase has not been observed. In the case of the Fe-V diffusion barrier it was shown that the use of the diffusion barrier resulted in smoother layers of β-FeSi2 than could be formed by direct reaction of Fe on Si. In the case of the Fe-Zr barrier it is found that the barrier fails structurally at high temperatures. While it does prohibit Fe diffusion at low annealing temperatures, significant Si diffusion occurs prior to ε-FeSi formation.