A reaction cell for ambient pressure soft x-ray absorption spectroscopy

Abstract

We present a new experimental setup for performing X-ray Absorption Spectroscopy (XAS) in the soft X-ray range at ambient pressure. The ambient pressure XAS setup is fully compatible with the ultra high vacuum environment of a synchrotron radiation spectroscopy beamline end station by means of ultrathin SiN membranes acting as windows for the X-ray beam and seal of the atmospheric sample environment. The XAS detection is performed in total electron yield (TEY) mode by probing the drain current from the sample with a picoammeter. The high signal/noise ratio achievable in the TEY mode, combined with a continuous scanning of the X-ray energies, makes it possible recording XAS spectra in a few seconds. The first results show the performance of this setup to record fast XAS spectra from sample surfaces exposed at atmospheric pressure, even in the case of highly insulating samples. The use of a permanent magnet inside the reaction cell enables the measurement of X-ray magnetic circular dichroism at ambient pressure.

THORONDOR: a software for fast treatment and analysis of low-energy XAS data

“…The nature of I 0 and I s clearly depends on the type of measurement. In the case of a TEY experiment, they consist of a current signal in the picoampere range (Castan-Guerrero et al, 2018). This procedure (i.e.…”

“…Under UHV conditions, it is possible to measure the photon flux I 0 impinging on the sample surface. This can be realized, for example, by measuring the TEY from a highly transparent metal grid intercepting a fraction of the incoming beam, typically localized before the entrance of the experimental chamber (Castan-Guerrero et al, 2018). In the case of ambient-pressure measurements, this important part of the XAS acquisition in UHV cannot be achieved because of the presence of both the cell membrane and the gas layer, which act as photon absorbers.…”

“…Although high-vacuum conditions produce an ideally clean environment for the sample under study, a multitude of chemically relevant phenomena take place only under ambient pressure (Castan-Guerrero et al, 2018;Escudero et al, 2013). In an effort to bridge the pressure gap in this context, different gas and liquid cells were designed in recent years, enabling soft X-ray studies of different reactions under in situ conditions (Blum et al, 2009;Castan-Guerrero et al, 2018;Escudero et al, 2013;Forsberg et al, 2007;Fuchs et al, 2008;Guo & Luo, 2010;Hä vecker et al, 1999;Knop-Gericke et al, 1998;Tamenori, 2013;Tokushima et al, 2009;Zheng et al, 2011;Beaumont, 2020). In general, their design implies that the X-ray beam penetrates the reaction volume through an Si 3 N 4 membrane a few tens of nanometres thick (Castan-Guerrero et al, 2018).…”

“…In an effort to bridge the pressure gap in this context, different gas and liquid cells were designed in recent years, enabling soft X-ray studies of different reactions under in situ conditions (Blum et al, 2009;Castan-Guerrero et al, 2018;Escudero et al, 2013;Forsberg et al, 2007;Fuchs et al, 2008;Guo & Luo, 2010;Hä vecker et al, 1999;Knop-Gericke et al, 1998;Tamenori, 2013;Tokushima et al, 2009;Zheng et al, 2011;Beaumont, 2020). In general, their design implies that the X-ray beam penetrates the reaction volume through an Si 3 N 4 membrane a few tens of nanometres thick (Castan-Guerrero et al, 2018). These membranes have sufficient mechanical resistance to the difference in pressure between the vacuum of the chamber, where the cell is situated, and the gas environment inside it, at atmospheric pressure (Escudero et al, 2013).…”

“…This last methodology, sometimes known as a 'fast-scan' or an 'on-the-fly scan', significantly improves the time resolution of the NEXAFS (near-edge X-ray absorption fine structure) measurements, allowing the user to follow different dynamic processes under in situ conditions (e.g. chemical reactions) (Castan-Guerrero et al, 2018). In line with the work by Stö hr (1992), we will use the term NEXAFS for soft X-ray absorption spectra (with an energy edge lower than 2 keV), and XANES (X-ray absorption near-edge structure) will be used to indicate absorption spectra referring to hard X-rays.…”