A metal vapour vacuum are (MEVVA) ion source is used for the fabrication of a gamma-Fe1-xNixSi2 (x approximate to 0.4) layer via the sequential implantation of Ni and Fe into (100) oriented silicon (Si) substrate. After annealing at 500 degrees C for 30 min, a "Fe0.6Ni0.4Si2/Fe0.4Ni0.6Si2/Si" structure appears. The Fe-rich Fe0.6Ni0.4Si2 has a beta-structure, while Ni-rich Ni0.6Fe0.4Si2 has the same unit cell as NiSi2 phase. The twinned beta-Fe0.6Ni0.4Si2 layer occurs predominantly in the orientation relationships with respect to the fluorite Fe0.4Ni0.6Si2. Increasing the temperature to 700 degrees C results in the presence of the mixture of beta-FeSi2, beta-Fe0.7Ni0.3Si2 and fluorite Fe0.3Ni0.7Si2. Annealing at 850 degrees C causes transition into the beta-FeSi2 and the fluorite Fe0.3Ni0.7Si2, The implantation at the same energy and sequence but with a double dose results in the separation of the original gamma-Fe0.6Ni0.4Si2 into beta-Fe1-xNixSi2 and fluorite Fe1-yNiySi2 phases.