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

Abstract

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.