Table-Top Ultrafast Soft X-Ray Spectroscopy Toward Synchrotron-like in-Situ Photoelectrochemical Measurements

Advancements in in-situ X-ray capabilities have enabled the measurement of electrochemical systems in more realistic operating conditions. While these measurements have progressed our understanding of electrochemical reactions from carrier dynamics to reaction mechanisms to degradation processes, they have mostly been limited to synchrotron facilities. However, performing in-situ table-top measurements has remained a challenge in the field. Table-top XUV spectrometers based on high-harmonic generation (HHG) are powerful tools for measuring ultrafast electronic and structural properties of photoelectrocatalysts ex-situ . However, extending the accessible energy range of HHG-based spectrometers beyond 300 eV is difficult due to inherent physical scaling laws. Laser-produced plasma sources can extend into the soft X-ray range to cover the water window. This capability could enable in-situ studies of photocatalysts, but their inherent source fluctuations have prevented ultrafast studies in the past. In this work, we employ methods pioneered by HHG-based setups to create a novel laser-produced plasma technique for table-top time-resolved measurements in the soft X-ray regime (200 – 1000 eV). We combine EMCCD detection, background-free self-referencing, edge-referencing analysis, amongst other advances, to reduce shot-to-shot noise so that sub-mOD signals are detectable. This presentation will also describe the technical advances pioneered at synchrotron sources that have enabled in-situ X-ray measurements of electrochemical systems. These advancements have inspired the effort to achieve the first table-top soft X-ray measurements in device-relevant liquid environments, enabling the correlation of photocatalyst properties, such as electron and hole energies and polarons, with photoelectrochemical product formation.