The Charge State of Iron Ions Implanted Into Sapphire
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THE CHARGE STATE OF IRON IONS IMPLANTED INTO SAPPHIRE C. J. MCHARGUE,* P. S. SKLAD,* C. W. WHITE,* G. C. FARLOW,** A. PEREZ,*** N. KORNILIOS,*** AND G. MAREST*** *Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37831 USA **Wright State University, Dayton, OH 45435 USA ***Universite Claude Bernard Lyon I, Villeurbanne Cedex, France ABSTRACT Single crystals of a-A1 2 03 were implanted with 5 7 Fe+ at room temperature to fluences ranging from 10"0 to 1017 ions/cm2 . The damage in the implanted zone and the valence states and local environment of implanted ions were studied by transmission electron microscopy, Rutherford backscattering-channelling, and conversion electron M~ssbauer spectroscopy. The implanted iron was distributed among the three charge states Fe2 +, Fe3 +, and Fe" (metallic clusters) with the relative amount of each varying with concentration of implanted iron. INTRODUCTION The use of ion implantation to modify the near-surface mechanical properties of ceramics is currently being explored at a number of laboratories [1-3]. The changes in hardness, apparent fracture toughness, and flexure strength have been qualitatively related to the damage microstructures. However, the variation in mechanical properties with concentration of implanted ion or between similar concentrations of different chemical species has not been accomplished because detailed information on the local defect structures has not been available. The nature of defects present in implanted insulating materials (ceramics) depends upon the residual charge state of the implanted species. In most studies to date, the implanted species has been a cation; therefore, there must be compensation for an excess positive charge. The use of conversion electron M~ssbauer spectroscopy (CEMS) has given insight into the local surroundings of iron implanted into MgO, LiF, and T10 2 [ref. 4-6]. By studying the variation in the relative amounts of the Fe3+, Fe2+, and Fel (metallic) charge states, these investigators were able to develop models for the defect structures. This work extends such studies to iron-implanted sapphire. EXPERIMENTAL CONDITIONS High-purity A1203 single crystals having normal to the surface were given an optical grade polish and then annealed 120 h at 1450 0C in flowing oxygen to remove any residual polishing damage. Following this treatment the crystals were almost defect free, as determined by Rutherford backscattering-channeling (RBS) measurements. The minimum yields, Xm (defined as the ratio of the backscattered yield from a c-axis aligned crystal to that of a random specimen), were 2% in the aluminum sublattice and 8% in the oxygen sublattice. Crystals were implanted at room temperature using a mass analyzed beam of 5 7 Fe 2 (160 or 100 keY). The fluences covered the range of 10"6 to 1017 ions/cm to give peak iron concentrations of 3 to 30% (of the cations). The crystals were implanted with the ion beam -70 off-normal to minimize channeling effects. Subsequently, the specimens were analyzed by RBS using 2 MeV He+ ions. Ma
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