Soft X-ray absorption spectroscopy (XAS) of liquid samples in transmission mode has been realized by developing a liquid cell [1, 2], where the liquid layer is sandwiched between two Si₃N₄ membranes and the liquid thickness is precisely controlled from 20 nm to 40 μm by adjusting the helium pressure around the liquid cell. As shown in the O K-edge XAS of liquid water at different thicknesses, the XAS spectra of various solutions over a wide concentration region can be measured using the precise thickness control method, where the liquid layer becomes thicker in the dilute solution, and vice verse, for obtaining the appropriate absorbance of soft X-rays.

1. M. Nagasaka et al., J. Electron Spectrosc. Relat. Phenom. 177, 130 (2010).
2. M. Nagasaka et al., J. Electron Spectrosc. Relat. Phenom. 224, 93 (2018).