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Resonant photoemission performed at the SRS Daresbury Laboratory is used to investigate the temperature- and doping-dependent spin states in single crystal LaCoO3(111) and La0.9Sr0.1CoO3(111). In an initial study, the surface reactivity of the LaCoO3(111) surface is investigated using H2O as a probe molecule. The results are used to interpret changes which may occur in the spectra as a function of time and temperature in UHV, due to surface reactions. This allows us to distinguish effects on the valence band spectra due to spin changes as a function of temperature. The temperature dependence of low binding energy features primarily associated with Co in the low spin (LS) state in LaCoO3 is investigated in detail. In particular, the intensity and onset energy of the Co 3p→3d resonance associated with these features is measured at small binding energy intervals. Delayed resonance onset associated with the LS state is consistently observed. This is used to locate the separate contributions of the low spin and higher spin states to the low binding energy spectrum. We find the contribution due to the LS state lies around 1 eV to lower binding energy than that due to higher spin states in LaCoO3. In contrast, we find the spectrum of La0.9Sr0.1CoO3(111) to be invariant with temperature, with no delayed resonance effect. The data are discussed in the light of recent models for the spin transitions, including the two stage spin-state model involving an intermediate spin state. Simulation of the temperature variation of the valence band spectra of LaCoO3 using this model provides good agreement with experiment.

The zero bias anomaly dependent on the preferred surface grain orientation of YBa2Cu3O7-δ ceramics has been investigated in the conductance curve of the tunneling characteristics. A tunnel junction was fabricated by evaporating Al metal onto the ceramics sample and then annealed to remove the oxygen-deficient layer. The preferred orientation and the oxygen deficiency on the surface were examined based on X-ray diffraction patterns and X-ray photoelectron spectra. There exist oriented grains with their c-plane parallel to the ceramics sample surface. These surface layers are oxygen-deficient. Using the junction fabricated on the oxygen-deficient grains, the zero bias anomaly appears on the dynamic conductance curve of the tunneling characteristics. This anomaly disappears when the junction is fabricated after mechanical polishing of the surface and annealed. One of the sources of zero bias anomaly is the existence of oxygen-deficient grains on the YBa2Cu3O7-δ surface.

The recovery of the electrode conductance for Au metal on YBa2Cu3O7-δ (YBCO) has been investigated. The reduction in the electrode resistance, which is defined as the inverse of the electrode conductance, was measured during heat treatment ranging from 150 to 280° C. The reduction has been characterized by two relaxation processes with activation energies of 0.52±0.04 and 1.40±0.03 eV. The former activation energy corresponds to that of the process in which the oxygen-deficient layer at the YBCO surface is replenished by oxygen diffusion from the bulk, and the latter to that of the process of rearrangement of Au atoms at the YBCO/Au interface which results in improved interconnections between Au metal and YBCO.