Thickness dependent valence fluctuation of CeN film

CeN films with different thickness are synthesized on a Re(0 0 0 1) substrate and studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy. A thickness dependent valence fluctuation is observed by XPS. Valence fluctuation only occurs with film thickness larger than a critical value of about 15 nm. This interesting phenomenon is mainly attributed to the stress in CeN films due to the large lattice mismatch between the CeN film and the substrate, and a possible composition deviation at the interface.