Development of a liquid flow cell to measure soft X-ray absorption in transmission mode: A test for liquid water

A liquid flow cell has been developed for the transmission-mode measurement of soft X-ray absorption spectra of liquid samples, and applied to bulk liquid water at the O K-edge region. Soft X-rays pass through the region filled by helium gas and then through the liquid sample, and finally reaches the detector in a helium atmosphere. Each region is separated by a 100 nm-thick SiNx membrane window, which is thin enough to transmit soft X-rays. The artifact of the higher order X-rays at the O K-edge region is evaluated by varying the sample thickness for 100-800 nm, and is removed successfully to obtain consistent soft X-ray absorbance for the liquid water. The sample thickness is estimated from the edge jump in absorbance. In the present cell, fresh liquid samples can be supplied to avoid the radiation damage. By changing the pressure of helium gas and the continuous flow speed of liquids, it is possible to control the thickness of liquid samples.