Modular soft x-ray spectrometer for applications in energy sciences and quantum materials

Abstract

Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components. The spectrometer's optics chamber can be used with gratings operated in either inside or outside orders, and the detector assembly can be reconfigured accordingly. The spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving power when using small source (∼1μm) and detector pixels (∼5μm) with high line density gratings (∼3000 lines/mm), or high throughput at moderate resolution. We report two such spectrometers with slightly different design goals and optical parameters in this paper. We show that the spectrometer with high throughput and large energy window is particularly useful for studying the sustainable energy materials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery cathode material LiNiCoMnO can be produced in few hours using such a spectrometer. Unlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the elemental absorption edges to determine various spectral features like the localized dd excitations and non-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying such RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes hard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this modular spectrometer design can serve as the platform for further customization to meet specific scientific demands.

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

“…The outgoing photon direction (momentum transfer) along the RIXS spectrograph is 90°. RIXS resolving power and other technical details of the VLS spectrograph used for this work can be find in our previous report 79 . Details on how the RIXS maps are generated are given in the Supplementary Methods.…”

Elucidating anionic oxygen activity in lithium-rich layered oxides

“…RIXS resolving power and other technical details could be find in our previous report. 73 Details of RIXS data processing is available in supplementary information. Hard XAS measurements for the Ru K-edge was performed at the Advanced Photon Source on beamline 20-BM-B in transmission mode with electron energy of 7 GeV and average current of 100 mA.…”

Diffraction gratings with two-orders-of-magnitude-enhanced dispersion rates for sub-meV resolution soft X-ray spectroscopy

“…1(b 2 ). The dispersion rate is two orders of magnitude larger than what is possible with man-made diffraction gratings at the same photon energy (Ghiringhelli et al, 2006;Strocov et al, 2010;Chaix et al, 2017;Brookes et al, 2018;Bisogni, 2019;Warwick et al, 2014;Chuang et al, 2017;Lai et al, 2014;Zhou, 2019;Dvorak et al, 2016). However, this comes at a high price of a factor of three reduced angular acceptance reduced to 0.24 mrad and of the energy bandwidth to 0.16 eV.…”

“…1(b) and 2(a). Using equation 9, we estimate D > 20 mrad meV À1 for E = 930 eV, assuming È 0 < $ 60 mrad, 2 the values, which are two orders of magnitude larger than those possible using manmade diffraction gratings (Ghiringhelli et al, 2006;Strocov et al, 2010;Chaix et al, 2017;Brookes et al, 2018;Bisogni, 2019;Warwick et al, 2014;Chuang et al, 2017;Lai et al, 2014;Zhou, 2019;Dvorak et al, 2016;Voronov et al, 2014Voronov et al, , 2015.…”

“…Angular dispersion rate D measures the angular variation of the propagation direction of the diffracted photon with its energy. It is primarily determined by the smallness of the diffraction grating period, or equivalently by the large value of the groove density g. The maximum angular dispersion rates of the state-of-the-art diffraction gratings is in the range D ' 0.2-0.4 mrad meV À1 at E ' 1 keV, corresponding to a groove density of g ' 5-10 mm À1 (Michette, 1986;Ghiringhelli et al, 2006;Strocov et al, 2010;Chaix et al, 2017;Brookes et al, 2018;Bisogni, 2019;Warwick et al, 2014;Chuang et al, 2017;Lai et al, 2014;Zhou, 2019;Dvorak et al, 2016;Voronov et al, 2014Voronov et al, , 2015.…”