Van Marum Colloquium - Pioneering techniques to probe the solid-liquid interface using the soft X-rays of the VerSoX beamline at Diamond Light Source
- Wednesday 31 May 2023
2333 CC Leiden
Beamline B07: Diamond Light Source’s Versatile Soft X-ray (VerSoX) suite for Applied Surface Science
At Diamond Light Source, the VerSoX (versatile soft X‑ray) beamline serves1,2 a wide community focused on applied surface science. Funded by the UK government and accessible for researchers world-wide, this bending-magnet beamline comprises two independently operating branches, with energy ranges of 45–2200 eV (B07B) and 110–2800 eV (B07C), welcoming first users in 2017 (B07C) and 2021 (B07B).
Branch B07C is designed for near-ambient-pressure (NAP) X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The typical operating pressure is 0.1–5 mbar. Gas handling is provided by an in-house developed “gas rig”, which can mix up to 14 gases using mass-flow controllers.
The endstation is connected to the beamline via a series of differential pumping stage, so the beam reaches the sample without the need for X-ray transparent membranes. The beamline entrance and the hemispherical analyser join in a single, central flange, additionally housing a photodiode for total fluorescence yield (TFY) XAS. To this flange, two different chambers can be connected, one of which can accommodate in situ gas/liquid cells.
The B07B branch line has two different endstations, a high-throughput UHV chamber for XPS/XAS and a dedicated ambient-condition XAS chamber. The XAS endstation (TEY/TFY) can be evacuated to high vacuum and samples can be measured up to several bar or in liquid environment using cells with X-ray-transparent SiNx-membranes.
This talk will emphasize on our recent efforts to probe the solid-liquid interface, via electron-yield XAS.3 In this technique, the sample is grown on thin (50–200 nm), free-standing SiNx membranes, which cap a three-electrode, flow cell. The solid-liquid interface is excited by the X-ray beam, which enters through the SiNx membrane. The XAS signal is collected via the drain current using a current amplifier. This setup was used to study the anatase TiO2–H2O interface, and it was found that (1) the signal is extremely sensitive to the interface (within a few nanometre) and (2) water forms an “ice-like” structure on the anatase. Recently, we used this to directly measure the ions in the electrochemical double layer and their disruptive effect on the interfacial water. I will conclude by discussing some challenging and how this technique relates to developments in related techniques.
1Ambient-pressure endstation of the Versatile Soft X-ray beamline at Diamond Light Source Held et al. J. Synchr. Rad. 27 (2020) 1153–1166
2The Versatile Soft X-ray (VerSoX) Beamline at Diamond Light Source
Grinter et al. Synchr. Rad. News 35 (2022) 39–47
3Interface Sensitivity in Electron/Ion Yield XAS: The TiO2–H2O Interface
Van Spronsen et al. J. Phys. Chem. Lett. 12 (2021) 10212–10217