X-Ray Photoelectron Spectroscopy of Spinodal Decomposition in Zn1-xCoxO: Composition Dependence of Electronic Structure and Sputtering-Induced Co

Spinodal decomposition may contribute to the interesting magnetic properties of diluted magnetic oxides such as cobalt-doped ZnO (Zn1-xCoxO), but little is known experimentally about the electronic structures of the resulting high concentration regions or how they may behave under various experimental probes. Here, X-ray photoelectron spectroscopy (XPS) is used to examine wurtzite Zn1-xCoxO crystallites (0.0 x 1.0) that model these high concentration regions. With increasing x, the valence band edge shifts to smaller binding energies and the cobalt 2p peaks shift to greater binding energies. Reduction of Co 2+ to Co 0 by argon ion (Ar + ) sputtering was also found to become markedly more facile with increasing x, placing spinodally segregated Zn1-xCoxO at greater risk of yielding false-positive Co 0 XPS signals than dilute Zn1-xCoxO with the same average composition.