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

Abstract

Thin iron films (120 or 240 nm thick) were amorphized by boron implantation up to doses 2 × 10 17 and 1 × 10 17 ions/cm 2 at energies 60 and 24 keV, respectively. Amorphized iron films were then implanted with nitrogen ions in dose range 5 × 10 16–4 × 10 17 ions/cm 2 at energies 32 and 75 keV. Thicker films were annealed at 200°C, 350°C and 500°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 Fe 2N phases at the expense of the crystalline α-Fe were formed. Annealing at 500°C leads to crystallization of a-(Fe–B,N) m through Fe 2B and γ ′-Fe 4N 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.