Soft X-ray absorption spectroscopy in the low-energy region explored using an argon gas window.

Masanari Nagasaka

doi:10.1107/s1600577520005883

Abstract

The soft X-ray region below 200 eV is important for investigating chemical and biological phenomena since it covers K-edges of Li and B and L-edges of Si, P, Sand Cl. Helium gas is generally used as the soft X-ray transmission window for soft X-ray absorption spectroscopy (XAS) under atmospheric conditions. However, the helium gas window cannot be applied to XAS in the low-energy region since transmitted soft X-rays mostly consist of high-order X-rays due to the low transmission of first-order X-rays. In this study, the argon gas window isproposed as a new soft X-ray transmission window in the low-energy region. High-order X-rays are removed by the absorption of the Ar L-edge (240 eV), and first-order X-rays become the major contribution of transmitted soft X-rays in the low-energy region. Under atmospheric argon conditions, the double-excitation Rydberg series of helium gas (60 eV), Si L-edge XAS of an Si3N4 membrane (100 eV) and S L-edge XAS of dimethyl sulfoxide gas (170 eV) are successfully measured, indicating that the argon gas window is effective for soft X-ray transmission in the low-energy region from 60 eV to 240 eV.

Highlights

Soft X-ray absorption spectroscopy (XAS) is an elementspecific method used to investigate local electronic structures of materials since it observes the excitation process of a core electron to unoccupied orbitals (Stohr, 1992)
We confirm the effectiveness of the argon gas window as a new soft X-ray transmission window in the low-energy region below 200 eV, which includes chemically and biologically important absorption edges such as the K-edges of Li and B and the L-edges of Si, P, S and Cl
Since argon gas removes the high-order X-rays above 240 eV due to the absorption of the Ar L-edges, XAS under atmospheric conditions is possible in the low-energy region from 60 eV to 240 eV

Summary

Introduction

Soft X-ray absorption spectroscopy (XAS) is an elementspecific method used to investigate local electronic structures of materials since it observes the excitation process of a core electron to unoccupied orbitals (Stohr, 1992). Since soft X-rays are strongly absorbed by air and liquids, XAS spectra of gas and solid samples under ultrahigh-vacuum conditions have been studied extensively. Several groups have measured XAS spectra under atmospheric conditions using the high soft X-ray transmission of helium gas (Chantler, 2000). A differential pumping system is used between a soft X-ray beamline under ultrahigh-vacuum conditions and a measurement chamber under atmospheric helium conditions (Lee et al, 2001; Gog et al, 2007; Tamenori, 2010). The helium gas window is generally used for soft X-ray transmission.

Methods

Conclusion