Two-stage diffusion was observed experimentally for the first time in polycrystalline alumina. Samples were heavily implanted with Ti ions, and the concentration depth profiles were determined by means of Rutherford back-scattering spectrometry with 2MeV He+ ions. The Arrhenius plot, as deduced from the Rutherford back-scattering spectra, exhibited 2 different diffusion mechanisms for the implanted Ti ions between room temperature and 900C. That is, radiation-enhanced diffusion occurred up to 730C, and transient thermal-like diffusion occurred between 730 and 900C. Extrapolation to 0 at 710C gave values which agreed well with published data. At this temperature, the annealing of F-centres was already complete. High-resolution scanning electron microscopy, with energy-dispersive X-ray analysis, revealed the presence of Ti-enriched nanoparticles having a typical diameter of 10 to 15nm in samples which had been implanted at room temperature. These nanoparticles agglomerated into larger particles at an implantation temperature of about 830C. More detailed information on the depth and lateral distributions of Ti atoms could be obtained by combining Rutherford back-scattering, high-resolution scanning electron microscopy and X-ray photo-electron spectroscopy measurements.

Two-Stage Diffusion and Nanoparticle Formation in Heavily Implanted Polycrystalline Al2O3. S.M.Duvanov, A.G.Balogh: Nuclear Instruments and Methods in Physics Research B, 2000, 171[4], 475-80