MICROSTRUCTURAL AND CHEMICAL EFFECTS IN AL2O3 IMPLANTED WITH IRON AT 77-K AND ANNEALED IN OXIDIZING OR REDUCING ATMOSPHERES

Implantation of Fe (160 keV) into alpha-Al2O3 at 77 K produces an amorphous surface layer for fluences in the range of 10(16) to 10(17) Fe/cm2. Measurements of short-range order were made by extended energy loss fine structure analysis (EXELFS). The structure of amorphous Al2O3 produced by implantation of iron at 77 K exhibits short-range order that differs from that produced by stoichiometric (Al + O) implants. This difference is manifested by changes in the Al-O near-neighbor bond length. The local environments of implanted iron were determined from conversion electron Mossbauer spectroscopy (CEMS). The iron resides in several different local environments consistent with the electronic states of Fe2+, Fe4+, and Fe0. The relative amount of each environment depends upon the concentration (fluence) of the implanted iron ions. Regrowth of the amorphous zone during annealing occurs in the sequence amorphous --> gamma-Al2O3 --> alpha-Al2O3. The kinetics of regrowth and phase separation vary with implanted fluence and with annealing atmosphere. The higher the concentration of implanted iron, the slower the formation of iron-aluminum oxide precipitate phases in oxidizing atmospheres and alpha-Fe precipitates in reducing atmospheres.