The charge state of titanium ions implanted into sapphire: An EXAFS investigation
X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) have been used to study the charge states and atomic environments of Ti+ ions implanted into a single crystal sapphire substrate. Fluorescence techniques have been shown capable of detecting signals from the implanted ions even though the implant density in the ∼100μm thick specimen used is ∼ 0.02 at% (the implant profile all being within 0.2μm of the surface). By comparison with TiO2, Ti2O3 and TiO standards, XANES data suggest that the implant species environment is disordered. Further, EXAFS Fourier transforms show that the first shell radius of the implant species is between that of the TiO and Ti2O3 standards. Again, this indicates considerable structural disorder. After annealing the implanted specimen in air at 1150° C for 2 h, a shift towards the shell radius of the TiO2 structure is observed together with a similar change in the XANES appearances. Our conclusion is that the initial titanium ion implant into sapphire exists in both the Ti2+ and Ti3+ charge states and is located in a range of sites in the radiation-damaged material. Annealing produces a shift in charge state towards Ti4+. Implications for the solid solution hardening effect of the implant in sapphire are discussed.