2019 Volume 62 Issue 9 Pages 564-567
X-ray photoelectron spectroscopy (XPS), which is capable of analyzing the elemental composition and the oxidation states of surfaces and interfaces placed in a vacuum, was applied to observe ionic species dissolved in aqueous solutions. An environmental cell using a 5-nm thick silicon nitride membrane as a quasi-transparent window for incident x-rays and emitted photoelectrons was developed, and cesium chloride aqueous solutions with a variety of concentrations enclosed in the cells were measured using a laboratory-based XPS apparatus equipped with an Al-Kα source. Cs 4d photoelectrons emitted from cesium ions in the solutions were detected passing through the membrane. Moreover, the peak intensity increased proportionally with the concentration of cesium chloride, proving that this technique allows us to conduct quantitative analysis of solution species.