Crystallisation and Diffusion in <001> Oriented Sapphire Amorphised by Zinc Ion Implantation
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CRYSTALLISATION AND DIFFUSION IN ORIENTED SAPPHIRE AMORPHISED BY ZINC ION IMPLANTATION. L.A. Bunn and D.K. Sood, Microelectronics and Materials Technology Centre, Victoria University of Technology, Royal Melbourne Institute of Technology, 124 La Trobe Street, Melbourne, Victoria 3001, Australia.
ABSTRACT High dose zinc implantation (1x10 1 6 to 6x10 1 6 ions/cm2 ) into c-axis sapphire at 77 K produces amorphous surface layer . Post-implantation annealing at temperatures at and above 800 C show that the modes of recrystallisation are strongly dependant on ion dose. At low doses formation of crystallites of a and 7 phase Al 0 is seen, with no evidence of any planar epitaxial growth a? ?he original crystalline-amorphous interface. The zinc is seen to diffuse isotropically within the crystallised layer and becomes partially substitutional within the crystallites. At high doses, however, the formation of crystallites is inhibited, with the layer remaining amorphous. A more rapid diffusion of zinc is seen in the amorphous A1 2 0 3 , with some of the zinc being lost at the surface.
INTRODUCTION Ion implantation and subsequent thermal annealing can be used to modify the near surface region of ceramics to create novel mechanical, chemical, optical and electrical properties [1]. These properties are influenced by the lattice damage, microstructure of the implanted layer, residual (compressive) stress, defect-impurity interactions and their behaviour during post-implantation annealing. Previous studies have shown that, a) lattice damage accumulates to amorphise Al 2 01 [2,3] at an optimum damage energy density, b) during annealing, intrinsic amorphous Al20 3 prepared by stoichiometric implants into c-axis AI 2 0 3 converts firstly to the y phase and then transforms to the a phase [2] by the outward motion of a well defined planar interface, and c) implanted species either undergo a recrystallisation driven migration towards the surface,or do not diffuse appreciably (3,4]. In this work we report on the study of annealing of amorphous surface layers on c-axis a-A1 2 0 3 . produced by high dose zinc implantation, and its dependance on ion dose and annealing temperature. Zinc was chosen as implant species because of its valence, ionic radius and electronegativity differing considerably from that of Al cation in Al 2 0 3 lattice. Thus the "chemical' role of the implanted species in affecting atomic transport/transformations during post implantation annealing may be studied.
Mat. Res. Soc. Symp. Proc. Vol. 201. c 1991 Materials Research Society
418
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EXPERIMENTAL Optically flat slices of c-axis Sapphire were preannealed at 1400 0 C for 120 hours in flowing 02 to remove any s 8 rface damage dye to polishing. The samples were implanted, at 77 K and withla 7 off-axis tilt, with 100key Zn ions to nominal doses of lxl6, 3x101 and 6x10 ions/cm . They were then annealed isothermally in a stepped sequence up to 24 hours in a flo
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