Depth analysis of phase formation in alpha-Fe after high-dose Al ion implantation

alpha-Fe surfaces were implanted at room temperature and at 300 degrees C w ith 50 keV Al ions with a nominal dose of 5 x 10(17) cm(-2). The samples we re studied in the as- implanted state and after annealing at 300 degrees C. The depth distribution of the Fe-Al phases formed was investigated nondest ructively at RT and at 40 K by depth-selective Fe-57-conversion-electron Mo ssbauer spectroscopy (DCEMS) in the energy range of K- as well as L-convers ion electrons. Integral conversion-electron Mossbauer spectroscopy (CEMS) w as performed between 30 K and RT. In addition, secondary neutral mass spect roscopy and depth-profiling Auger-electron spectroscopy were employed for i nvestigating the element-concentration depth profiles which were observed t o extend deeper than Monte Carlo simulations predict. We found an atomicall y disordered magnetic and an atomically disordered nonmagnetic bcc phase in the as-implanted state the composition of which can be explained by the Al -concentration dependence of bulk disordered Fe-Al alloys. After annealing the nonmagnetic phase becomes atomically ordered (B2 structure) whereas the magnetic phase stays in the atomically disordered state. The layer-like st ructure of the two phases observed after annealing can be described by the magnetic phase diagram of ordered Fe-Al alloys. (C) 1998 American Institute of Physics. [S0021-8979(98)05524-8].