Copper and copper oxides (Cu2O and CuO) have been deposited by evaporation of copper and subsequent oxidizing treatments, on the surface of flat SiO2 and ZrO2 substrates. Large variations of several eVs have been found in the values of the Cu 2p3/2 binding energy (BE) and Auger parameter (α‘) of copper as a function of the amount of deposited metallic copper or copper oxides. The magnitude of the changes was also dependent on the type of support upon which the experiment was carried out. These changes have been attributed to modifications in the factors contributing to the initial and final state effects of the process, according to the dispersion degree and the nature of the interactions between the copper oxide moieties and the support. All of these changes can be systematized with the help of chemical state plots. Experiments carried out with real catalysts stress the need of such plots, which summarize the results obtained with the model systems, for a proper characterization of the supported oxide phases in this kind of real materials.

Herein we present a combined study of the evolution of both the photoluminescence (PL) and the surface chemical structure of organic metal halide perovskites as the environmental oxygen pressure rises from ultrahigh vacuum up to a few thousandths of an atmosphere. Analyzing the changes occurring at the semiconductor surface upon photoexcitation under a controlled oxygen atmosphere in an X-ray photoelectron spectroscopy (XPS) chamber, we can rationalize the rich variety of photophysical phenomena observed and provide a plausible explanation for light-induced ion migration, one of the most conspicuous and debated concomitant effects detected during photoexcitation. We find direct evidence of the formation of a superficial layer of negatively charged oxygen species capable of repelling the halide anions away from the surface and toward the bulk. The reported PL transient dynamics, the partial recovery of the initial state when photoexcitation stops, and the eventual degradation after intense exposure times can thus be rationalized.

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