Operation of a bending magnet beamline in large energy bandwidth mode for non-resonant X-ray emission spectroscopy

Olga Dikaya,Maarten Nachtegaal,Jakub Szlachetko,Kathrin Ebner,Viktoriia Saveleva,Nicola Weder,Benjamin Probst,Roger Alberto,Dmitrii Serebrennikov,Evgeny Clementyev,Ksenia Maksimova,Alexander Goikhman,Grigory Smolentsev

doi:10.1016/j.rinp.2020.103212

Abstract

Two new operation modes, “pink beam” excitation, which has the energy bandwidth defined by X-ray mirrors and filters, and “broadband beam”, where the energy bandwidth is defined by the reflection from a multilayer monochromator, were implemented at the SuperXAS beamline of the Swiss Light Source (SLS). These setups allow measuring non-resonance X-ray emission spectra (XES) with 2–3 orders of magnitude higher incident flux than non-resonant XES measurements with a monochromatic incident beam. For the broadband beam mode, a Mo/Si multilayer structure was designed, with which the energy can be tuned in the 5–17 keV range. The multilayer demonstrates a relatively large energy bandwidth of 4 ± 0.2% through the whole energy range and a reflectivity of 23–60%, which increases with energy. We show that by using pink beam mode one can investigate the electronic structure of photocatalytic intermediates through time-resolved core-to-core XES experiments of diluted samples with a concentration of the element of interest of ~1 mM. Broadband beam mode is optimal for valence-to-core XES experiments and allow to avoid the excitation of additional KLβ satellites that can complicate the interpretation of spectra.

Highlights

X-ray emission spectroscopy (XES) is a technique that is complementary to X-ray absorption spectroscopy (XAS) and provides valuable information on the local electronic structure of materials and their chemical composition
In application to non-resonance XES experiments, the bending magnet beamlines can profit from the large energy bandwidth of the source and deliver incident X-ray fluxes comparable to those achieved at undulator stations
We demonstrate the optimization of a bending magnet beamline for non-resonance XES measurements using pink and broadband beam operation modes

Summary

Introduction

X-ray emission spectroscopy (XES) is a technique that is complementary to X-ray absorption spectroscopy (XAS) and provides valuable information on the local electronic structure of materials and their chemical composition. XES is a powerful tool to study the electronic structure of the element of interest in crystals, dissolved compounds, amorphous samples and other non-crystalline forms of materials [1]. Monochromatic excitation with energies around the X-ray absorption edge is required for these measurements [2,3,4,5]. High energy-resolved off-resonant XES spectra (HEROS) reflect the projected empty density of states similar to the X-ray absorption near edge structure (XANES) [6]. Such an approach is promising for applications at X-ray free-electron lasers and for measuring samples in fluorescence mode free of self-absorption effects [7]. Experiments that are more challenging and require high flux are valence-to-core XES and time-resolved (laser pump – X-ray probe) XES experiments for which

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