Photoemission studies of a cleaved CuO single crystal have been carried out, using station 6.2 at the CLRC Daresbury Laboratory. The (100) face orientation produced by anvil cleaving was determined using Laue back-reflection and LEED. Resonant photoemission measurements at the Cu 3pCu 3d threshold were undertaken and these are compared with existing data from oxidized copper films, and with theoretical configuration interaction calculations for the resonance process. Angle-resolved measurements of the valence band structure have also been performed at different photon energies along three crystal axes, and these are mapped onto the 3D structure of the monoclinic material. This allows general comparison with existing momentum-resolved calculations. The validity of comparisons with both localized and delocalized descriptions of the electronic structure of this highly correlated oxide is discussed.

Ceramic samples of La, -,Sr,Ni, -,Fe,O, + d , designed to model the ICI Hydecat catalyst, have been prepared via precipitation followed by high temperature annealing. The samples are characterized by X-ray diffraction, EDAX and atomic absorption spectrometry. The small changes in electronic structure as a function of x and y have been probed using photoemission.This reveals a progressive shift of the valence-band edge towards the Fermi level as a function of Sr-doping level, consistent with the approach to a metal to non-metal transition. Resonant photoemission at the Fe and Ni 3p thresholds is used to identify the transition metal contributions to the valence band density of states, and confirms a valence state of 33.0 for Fe. High resolution ESCA is used to quantify the surface composition of the samples, revealing Sr segregation consistent with that found in related perovskites and layered perovskites. Adsorption of CO onto the surfaces of these materials is seen to give rise to the ready production of a carbonate species. Water adsorption studies, which test the potential stability of the materials for possible applications in aqueous solution, are also presented.

Synchrotron-excited resonant-photoemission measurements at rare-earth 4d ~ 4fand transition-metal 3p ~ 3d thresholds have been carried out using a variety of complex cuprates and nickelates on stations 6.1 (grazing-incidence monochromator) and 6.2 (toroidal-grating monochromator) at the SRS CLRC Daresbury Laboratory. The systems studied are Nd2Nil _xCuxO4, La2_xSrxNil _yFeyO4 + 6 and Bi2Sr/Cal_xYxCu208 + 6. A combination of EDC and constant-initial-state data is used to examine the 4f and 3d contributions to the valence-band density of states and their binding-energy positions relative to the Fermi energy. This allows the study of the valence states of the transitionmetal ions and their modulation on doping. For La2_ xSrxNii _ yFeyO4 + 6, this approach is used to infer a valence state of _> 3.0 for Fe. In the case of Bi2Sr2Cal _ xYxCuz08 + 6, the effect of Cu valence modulation on the 3p resonance is observed as x is varied. This is discussed in the light of controversy surrounding shifts in core-level photoemission with doping for this system.

One-dimensional quasiperiodic optical systems are studied, using a Schrödinger-like equation with a potential V(x)=2lambda(1) cos x+2lambda(2) cos alphax as an approximation to the wave equation in the slowly-varying wave approximation. It is shown that small changes in the parameter alpha produce major changes in the band structure of the system. For certain values of alpha, the band structure consists of many "thin bands" and allows the possibility of dense multiplexing. The propagation of "noisy optical waves" that contain many frequencies with a thermal distribution is also studied with a thermodynamic model. Quantities like the thermodynamically averaged group velocity and the thermodynamically averaged inverse effective mass are introduced in order to quantify the complex relation between the frequency and wave vector in these systems.

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