AN NEXAFS INVESTIGATION OF THE REDUCTION AND REOXIDATION OF TIO2(001)

The near-edge X-ray absorption fine structure (NEXAFS) technique was a pplied to characterize the oxidation stares of titanium cations on TiO 2(001) surfaces reduced by argon-ion bombardment and reoxidized by the rmal treatment. Although many characterization studies of reduced TiO2 have been performed, none of these has applied both surface-sensitive (electron yield) and bulk-sensitive (fluorescence yield) NEXAFS to ch aracterize reduced TiO2(001) single-crystal surfaces. The fluorescence yield NEXAFS of polycrystalline samples of the suboxides TiO and Ti2O 3 were used as standards to fingerprint reduced cations on the TiO2(00 1) surface. NEXAFS has allowed us to estimate the concentration of oxy gen and titanium in the near-surface region of reduced and reoxidized samples. The results of this study demonstrate that oxygen is preferen tially removed during ion bombardment, that the depth of the altered l ayer is comparable to the ion penetration depth, and that the electron ic environment of cations in the altered layer is comparable to that o f cations in titanium suboxides. The extents of reduction calculated f rom NEXAFS results for reduced and reoxidized surfaces as a function o f annealing temperature compare favorably with those previously determ ined by analysis of Ti 2p XPS data. (C) 1998 Elsevier Science B.V.