Synchrotron radiation studies of H2O adsorption on TiO2(110)

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Synchrotron radiation photoemission has been used to study the interaction of H2O with defective and nearly-perfect TiO2(110) surfaces at temperatures between 160 and 300 K. Ti3+ 3d defect sites are implicated in the adsorption process, and by tuning the photon energy to 47 eV we find that a resonant photoernission process gives an enhanced photoermission sensitivity to the 3d defect states. Defects are produced on TiO2(110) by annealing to 1000 K in UHV; subsequent exposure to 104 L O2 produces nearly perfect surfaces, based on the suppressed Ti3d emission. Both nearly perfect and defective surfaces give rise to dissociative adsorption of H2O at 300 K. The saturation coverages are near 0.1 ML, independent of the initial defect concentration; however, the rate of dissociative adsorption (sticking probability) is higher on defective surfaces. The enhanced sensitivity to the Ti3+ defect states has allowed the observation of a surprising effect; the dissociative adsorption of H2O results in increased defect state intensity on the nearly perfect surfaces. This apparent charge-transfer to the substrate implies that a new model for the dissociation process on oxide surfaces is needed. At 160 K H2O adsorbs molecularly on both the nearly-perfect and the defective surfaces. Subsequent annealing experiments allow estimates of the interaction energies involved in the dissociation process. © 1989.

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Surface Science

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