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We present a study of the growth of the p-type inorganic semiconductor CuI on n-type TiO2 anatase single crystal (101) surfaces and on nanoparticulate anatase surfaces using synchrotron radiation photoemission spectroscopy. Core level photoemission data obtained using synchrotron radiation reveal that both the substrate (TiO2) and the overlayer (CuI) core levels shift to a lower binding energy to different degrees following the growth of CuI on TiO2. Valence band photoemission data show that the valence band maximum of the clean substrate differs from that of the dosed surface which may be interpreted qualitatively as due to the introduction of a new density of states within the band gap of TiO2 as a result of the growth of CuI. The valence band offset for the heterojunction n-TiO2/p-CuI has been measured using photoemission for both nanoparticulate and single crystal TiO2 surfaces, and the band energy alignment for these heterojunction interfaces is presented. With the information obtained here, it is suggested that the interface between p-CuI and single crystal anatase-phase n-TiO2 is a type-II heterojunction interface, with significant band bending. The measured total band bending matches the work function change at the interface, i.e., there is no interface dipole. In the case of the nanoparticulate interface, an interface dipole is found, but band bending within the anatase nanoparticles remains quite significant. We show that the corresponding depletion layer may be accommodated within the dimension of the nanoparticles. The results are discussed in the context of the functional properties of dye-sensitized solid state solar cells. [ABSTRACT FROM AUTHOR]

The catalytic properties of LaCoO[sub 3] in the oxidation of organic molecules in aqueous solution are explored as a function of doping with both Sr substitution for La and Fe and Ni substitution for Co. VUV photoemission is used to explore the surface reactivity of the ceramic catalysts in aqueous solution, using H[sub 2]O as a probe molecule. These measurements are complemented by EXAFS and XANES measurements designed to probe the local defect structure and by GC measurements of catalytic activity in the aqueous epoxidation of crotyl alcohol. We relate the observed catalytic activity to the defect structure of the doped materials. In Ni-doped materials, oxygen vacancies appear to be the predominant defect, whereas in Fe-doped samples, electron holes are stabilised on Fe, leading to very different behaviour in oxidation. The surface reactivity to water is also influenced by the TM d electron count, with water binding more strongly to Fe-doped materials than to those containing Ni. The influence of these factors on the rate of the unwanted hydrogen peroxide decomposition reaction and hence on activity in epoxidation is discussed. [ABSTRACT FROM AUTHOR]

BaPb[sub 1-x]Bi[sub x]O[sub 3] crystals, doped to various nominal x, were investigated in a scanning transmission electron microscope equipped with energy dispersive x-ray and electron energy loss spectroscopy facilities. Large compositional variations on the nm scale were found in single crystalline regions of any nominal x value. These were accompanied by changes in the core-loss and low-loss energy loss spectra. The low-loss energy loss spectra, furthermore, demonstrate the evolution of electronic structure with doping (i.e., transitions from semiconductor to semimetal) and fluctuations with variations in the local composition. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Time-resolved laser-pump X-ray-photoemission-probe spectroscopy of a ZnO (1010) substrate with and without PbS quantum dots (QDs) chemically linked to the surface is performed, using laser photon energies resonant with and below the band gap energy of the substrate (λ=372 and 640 nm, hv =3.33 and 1.94 eV). Charge injection from the photoexcited QDs to ZnO is demonstrated through the change in the surface photovoltage of the ZnO substrate observed when the heterojunction is illuminated with 1.94 eV radiation. The measured carrier dynamics are limited by the persistent photoconductivity of ZnO, giving dark carrier lifetimes of the order of 200 µs in a depletion layer at the interface. The chemical specificity of soft X-rays is used to separately measure the charge dynamics in the quantum dots and the substrate, yielding evidence that the depletion region at the interface extends into the PbS QD layer. [ABSTRACT FROM AUTHOR]

An XUV beamline has been constructed on the SRS synchrotron radiation source at Daresbury Laboratory, exploiting the output from a 2 T multi-pole wiggler. The beamline is based on an SGM design and produces photons in the energy range 40-350 eV. By taking a 7.5 mrad fan, a high flux of between 1 × 10[sup 13] and 1 × 10[sup 14] photons/s/300 mA ring current can be delivered, with a resolving power of around 1000. A Kirkpatrick-Baez mirror pair focuses the light onto the entrance slit of the monochromator. Using 10 · m entrance and exit slits, a resolving power of up to 10,000 can be achieved, with a flux of 0.5-2 × 10[sup 11] photons/s/300 mA. The calculated and measured performance is presented, with emphasis on the challenges associated with utilizing the XUV output of a high field MPW source. In addition, the scientific research programme is outlined. [ABSTRACT FROM AUTHOR]