Electronic structure and surface reactivity of La1-xSrxCoO3

Resonant photoemission performed at the SRS Daresbury is used to investigate the temperature- and doping-dependent spin transitions in single crystal samples of the La1-xSrxCoO3 system (x=0, x=0.1). For LaCoO3, the measurements taken over a wide temperature range are interpreted in the light of current models for the spin transitions. The Sr-doped compound is found to be in the same spin state at all temperatures. The temperature dependence of low binding energy features primarily associated with Co in the low spin state is investigated in detail. In particular, the intensity and onset energy of the Co3p→3d resonance associated with these features is measured at small binding energy intervals. This is used to locate the separate contributions of the low spin and higher spin states to these signals. In addition, the surface reactivity of the LaCoO3 (111) surface is investigated using H2O as a probe molecule, and the results are used to interpret changes which may occur in the spectra as a function of time in UHV.