QUESTION OF SUPEROXIDE IN LA2CUO4+DELTA

It has recently been suggested that superoxide plays a role in the superconductivity of oxygen-enriched La2CuO4+. The x-ray photoelectron spectroscopy (XPS) identification of the superoxide is crucial in these arguments. In recent experiments we have deposited Li on solid O2, and from these data we are able to reliably identify the superoxide, peroxide, and oxide in the XPS spectra of this relatively simple system. Our identification of the superoxide peak at 534.5 eV does not agree with the value of 532 eV given by others for La2CuO4+. Furthermore, the O 1s spectrum we obtained for La2CuO4+ shows only a single peak at 529 eV with no evidence of superoxide. This is of course expected for small. © 1990 The American Physical Society.