Sputtering-induced Co 0 formation in x-ray photoelectron spectroscopyof nanocrystalline Zn 1 - x Co x O spinodal enrichment models

Nanoscale enrichments resulting from spinodal decomposition have been proposed to contribute to the interesting magnetic properties of diluted magnetic oxides such as cobalt-doped ZnO ( Zn 1 - x Co x O ) , but little is known experimentally about the electronic structures or physical properties of such enrichments. Here, x-ray photoelectron spectroscopy (XPS) is used to examine wurtzite Zn 1 - x Co x O crystallites over the full composition range ( 0.0 ≤ x ≤ 1.0 ) that serve as models of the proposed spinodal decomposition nanostructures within Zn 1 - x Co x O bulk materials. With increasing x , the valence band edge shifts to smaller binding energies and the cobalt 2 p peaks shift to greater binding energies, providing spectroscopic signatures that may allow identification of spinodal decomposition in bulk Zn 1 - x Co x O . Reduction of Co 2 + to Co 0 by argon ion ( Ar + ) sputtering was also found to become markedly more facile with increasing x , suggesting that locally-enriched Zn 1 - x Co x O is at greater risk of yielding false-positive Co 0 XPS signals than uniformly dilute Zn 1 - x Co x O with the same overall composition.