Modern X-ray spectroscopy: XAS and XES in the laboratory

Abstract

X-ray spectroscopy is an important tool for scientific analysis. While the earliest demonstration experiments were realised in the laboratory, with the advent of synchrotron light sources most of the experiments shifted to large scale synchrotron facilities. In the recent past there is an increased interest to perform X-ray experiments also with in-house laboratory sources, to simplify access to X-ray absorption and X-ray emission spectroscopy, in particular for routine measurements. Here we summarise the recent developments and comment on the most representative example experiments in the field of in-house laboratory X-ray spectroscopy. We first give an introduction and some historic background on X-ray spectroscopy. This is followed by an overview of the detection techniques used for X-ray absorption and X-ray emission measurements. A short paragraph also puts related high energy resolution and resonant techniques into context, though they are not yet feasible in the laboratory. At the end of this section the opportunities using wavelength dispersive X-ray spectroscopy in the laboratory are discussed. Then we summarise the relevant details of the recent experimental laboratory setups split into two separate sections, one for the recent von Hamos setups, and one for the recent Johann/Johansson type setups. Following that, focussing on chemistry and catalysis, we then summarise some of the notable X-ray absorption and X-ray emission experiments and the results accomplished with in-house setups. In a third part we then discuss some applications of laboratory X-ray spectroscopy with a particular focus on chemistry and catalysis.

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

“…Prime examples of operando applications encompass reforming, hydrodesulfurization (HDS), hydrogenation, selective oxidation, and automotive catalysis, covering a wide range of materials (e.g., zeolites, sulfides, oxides, supported transition and noble metal clusters/nanoparticles). [ 51–55,85,126–131 ]…”

In situ characterizations of solid–solid interfaces in solid‐state batteries using synchrotron X‐ray techniques

“…The lab X‐rays are generated from an X‐ray tube usually with a stationary or rotating anode, where the X‐rays are produced by accelerating electrons and colliding them with a metal anode target (e.g., Cu, Al, Mo, etc.) 21,22 . A broad spectrum of X‐rays known as bremsstrahlung radiation is produced by the decelerating electrons during the collision with the metal anode.…”

“…Although the production of X‐rays through the metal targets is the most common method in a laboratory setting, the efficiency, which is defined as the ratio of the electronic energy converted into photons to the electronic energy converted into heat, is very low even for the high‐flux rotating anodes. Only ~1% of the energy is converted into light, while the other 99% is dissipated as heat 22 . The efficiency is directly related to the accelerating voltage.…”

“…The efficiency is directly related to the accelerating voltage. However, this is limited by the melting point of the anode material 22 …”

“…The most intense and brilliant X‐rays are produced at synchrotron light sources. The brilliance of the X‐ray beams produced at these facilities is 14–20 orders of magnitude higher than that of the standard X‐ray tubes 22 . The photons are produced by circulating electrons along a large ring at >99.999% of the speed of light.…”