Transformation of amorphous a-(Fe-B) phase during nitrogen implantation

Thin iron films (120 or 240 nm thick) were amorphized by boron implantation up to doses 2x1017 and 1x1017 ions/cm2 at energies 60 and 24 keV, respectively. Amorphized iron films were then implanted with nitrogen ions in dose range 5x1016-4x1017 ions/cm2 at energies 32 and 75 keV. Thicker films were annealed at 200 deg. C, 350 deg. C and 500 deg. C after the implantation process. Implanted films were investigated by CEMS, AES and XPS methods. It was found that multi-energy implantation results in almost flat nitrogen and boron distribution. Investigations show that for low nitrogen doses an amorphous a-(Fe-B,N)m phase dominates in CEMS spectra. When the nitrogen concentration exceeds the boron one paramagnetic (Fe-B,N)p and Fe2N phases at the expense of the crystalline α-Fe were formed. Annealing at 500 deg. C leads to crystallization of a-(Fe-B,N)m through Fe2B and γ'-Fe4N formation. The formation of chemical bond of B-N type was observed by AES and XPS in iron films with equal boron and nitrogen concentrations