An X-ray photoelectron spectroscopy study of BaAl2S4 thin films

Depth profiling with X-ray photoelectron spectroscopy (XPS) was used to study BaAl2S4:Eu thin films, which were prepared as a multi-layered stack of electron beam deposited BaS:Eu and Al2S3 thin films. A post-deposition thermal annealing at 900 °C was performed to obtain full reaction towards BaAl2S4:Eu. Depth profiles were recorded for both as-deposited and annealed thin films. The influence of exposure to ambient air prior to and after ex situ annealing on the composition of the films is discussed. XPS photoline positions and shapes are interpreted to understand the formation and degradation of BaAl2S4:Eu. Such information is highly important for the optimisation of BaAl2S4:Eu thin films as the blue emitter in inorganic thin film electroluminescent displays.