AMORPHIZATION OF SAPPHIRE DURING ION-BEAM MIXING

Earlier studies indicated that implantation of zirconium into sapphire at room temperature produced an amorphous layer at a critical composi tion of approximately 6.5% (cation). Further insight into the amorphiz ation of sapphire has been provided by ion beam mixing studies. Bi-lay er couples of approximately 80 nm thick polycrystalline ZrO2 films dep osited on the (0001) face of alpha-Al2O3 single crystals were irradiat ed to 4 x 10(16) ions/cm2 with Kr (475 keV, 20-degrees-C) or Cr (340 k eV, 20-degrees-C or approximately 900-degrees-C). Transmission electro n microscopy showed the unirradiated couples to have sharp, planar int erfaces between the films and substrates. Recoil mixing by both ion sp ecies gave Zr concentrations greater than 10% (cation) to depths of 10 -20 nm. An amorphous layer containing Zr was present at the interface for samples irradiated at room temperature. The sample mixed at the el evated temperature contained a sharp interface similar to the as-depos ited sample. The present results suggest that both irradiation-produce d damage (defects) and certain chemical species are required to amorph ize sapphire.