Development of Fluorescence XAFS System in Soft X-Ray Region Toward Operando Conditions Using Polycapillary X-Ray Lens

摘要

We developed a fluorescence XAFS system toward operando conditions using soft x-ray radiation at KEK-PF BL-27A.X-ray adsorption fine structure (XAFS) analysis in the soft x-ray region is useful for elucidating molecular structures in both atmosphere and solutions.Particularly, light elements play an important role in many cases in this energy region.The attenuation of soft x-rays in a solution is large compared to that of hard x-rays.Thus, appropriate spectral statistics cannot be obtained in the soft x-ray region.Recently, using fluorescence XAFS measurement at the S K-edge (2.4 keV), we found that biological molecules containing sulfur atoms adopt specific molecular structures under different pH conditions in a solution.However, the diameter of the beam of this beam line at BL-27A was large, leading to difficulties in uniformly irradiating only the sample surface.Therefore, it was necessary to uniformly irradiate samples using a small-area x-ray beam.To collimate the beam and improve its intensity, we installed an x-ray focusing device.Herein, we introduce a light-collecting device that uses a polycapillary x-ray lens to focus soft x-rays.After installing this lens, we confirmed that focused x-rays and a higher-intensity beam were achieved.We conclude that focusing x-rays using a polycapillary lens in the soft x-ray region is an effective method for obtaining better spectral statistics in fluorescence XAFS measurements.