Crystallization, Diffusion and Phase Separation in Sapphire Amorphised by Indium Ion Implantation
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CRYSTALLIZATION, DIFFUSION AND PHASE SEPARATION IN SAPPHIRE AMORPHISED BY INDIUM ION IMPLANTATION
D.X. CAO*, D.K. SOOD AND A.P. POGANY, Microelectronics Technology Centre, Royal Melbourne Institute of Technology, GPO Box 2476V, Melbourne 3001, Australia. Permanent address: Institute Shanghai, P.O. Box 8204, China.
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ABSTRACT Indium implantation into a-axis sapphire to peak concentrations of 8-45 mol % In produces amorphous surface layers.Migration of In during isothermal 0 annealing at 600 C shows a strong ion dose dependence. For a dose of 6 2 6xlOl 1n/cm , two distinct types of In migration are seen - a) rapid diffusion of In within amorphous A1 2 0 3 and b) diffusion of In into crystalline A1 2 0 3 underlying the amorphous layer. For doses lower than 3x10 1 6 1n/cm2 , no such migration of In is seen under identical anneal conditions. However, In undergoes phase separation into crystalline In20 3 particles embedded in amorphous A1 2 0 3 at all doses. INTRODUCTION Surface modification of ceramics by ion implantation is being used to create novel optical, chemical, mechanical and electrochemical properties [1]. Many of these properties are influenced by the lattice damage, defect solute interaction and the behaviour of damage and solute atoms during post-implantation annealing. Previous studies on ion implanted A1 2 0 3 have shown - a) lattice damage accumulates to amorphise A1 2 0 3 [2,3] at an optimum damage energy density, b) during annealing, amorphous A1 2 0 3 converts first to the V-phase which then transforms to thea-phase [2] by the outward motion of a well defined planar interface, c) implanted species either undergo a recrystallization - driven migration outwards to the surface or do not diffuse appreciably [3,4]. In this work we report on a study of annealing of amorphous surface layers produced by indium implantation to high concentrations (up to 45 mol % In) in a-axis A1 2 0 3 . Crystallization, In diffusion and phase separation are studied in detail. We also provide, to the best of our knowledge for the first time, evidence of isotropic diffusion of an implanted species within the amorphous A12 03 layer and also into the underlying crystalline sapphire. This is accomplished by furnace annealing at 600 0 C - a temperature where no appreciable 8 crystallization (l1Onm/sec) of the amorphous layer is expected [2], for a self ion implanted A1 2 0 3 . EXPERIMENTAL The optically flat, a-axis A1 2 0 3 single crystals used were preannealed at 0 1400 C in an oxygen environment for 5 days, so that the sapphire slices were damage free. The indium ion implantation was carried out at 77 0 K, the chamber 7 vacuum was about 5x10- Torr. The energy used was 100 keV for doses of lxl016 , 6 16 2 3xlO1 and 6x10 In/cm . Isothermal annealing was performed in Ar gas at 0 600 C for 1,3,5,7 and 24 hours. Samples were analysed using techniques of Rutherford Back-Scattering and Channeling (RBSC), and Reflection High Energy Electron Diffraction (RHEED).
Mat. Res. Soc. Symp. Proc. Vol,
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