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.
The low temperature hidden order state of URu2Si2 has long been a subject of intense speculation, and is thought to represent an as yet undetermined many-body quantum state not realized by other known materials. Here, X-ray absorption spectroscopy (XAS) and high resolution resonant inelastic X-ray scattering (RIXS) are used to observe electronic excitation spectra of URu2Si2, as a means to identify the degrees of freedom available to constitute the hidden order wavefunction. Excitations are shown to have symmetries that derive from a correlated 5f 2 atomic multiplet basis that is modified by itinerancy. The features, amplitude and temperature dependence of linear dichroism are in agreement with ground states that closely resemble the doublet Γ5 crystal field state of uranium.The low temperature hidden order (HO) phase of URu 2 Si 2 has been a mystery for more than 25 years, and is widely anticipated to represent a novel manybody quantum state. When cooling through T HO =17.5K the material undergoes a second order phase transition, with a large loss of entropy that cannot be immediately explained by observed changes in the electronic structure [1][2][3][4]. Pinpointing the microscopic cause of this entropy change is challenging because basic properties of the atomic scale wavefunction are not decisively known. Experiments differ on whether the uranium valence state is closer to U 4+ (5f 2 ) [5,6] or U 3+ (5f 3 ) [7]. Proposed models have considered a wide range of local [8][9][10][11][12][13][14][15][16][17][18][19][20] and itinerant [21][22][23][24][25][26][27][28][29] low energy state bases for 5f electrons, and explored many exciting possibilities for the "hidden" quantum state. Here, high resolution (δE∼35meV) resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) are used to measure fundamental excitations created by resonance with the uranium 5d core level (O-edge), to identify what electronic degrees of freedom are relevant for effective models of hidden order, and what degrees of freedom are energetically gapped out.Measurements were performed on both a pristine crystalline surface cleaved in ultra high vacuum, and a cleaved surface that was oxidized by exposure to air at room temperature, promoting U 4+ valence. The dominant spectral features observed from both surfaces are shown to derive from the excitations of a freestanding 5f 2 U 4+ atom, revealing that atomically correlated Hund's rule interactions play a key role in determining the electronic degrees of freedom that can contribute to the hidden order state. However, some low energy excitations of the pristine surface are found to be extremely short lived, implying that the symmetries they represent are not strictly eliminated from the hidden order ground state. Linear dichroism in the XAS spectrum is consistent with the crystalline electric field (CEF) doublet state Γ 5 , but inconsistent with CEF singlet ground states that have been predicted as the basis of hidden order (e.g. Γ 1 , Γ 2 , Γ 3 ).Measuring XAS at the O-e...
SPECIES is an undulator-based soft X-ray beamline that replaced the old I511 beamline at the MAX II storage ring. SPECIES is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine-structure (NEXAFS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) experiments. The beamline has two branches that use a common elliptically polarizing undulator and monochromator. The beam is switched between the two branches by changing the focusing optics after the monochromator. Both branches have separate exit slits, refocusing optics and dedicated permanent endstations. This allows very fast switching between two types of experiments and offers a unique combination of the surface-sensitive XPS and bulk-sensitive RIXS techniques both in UHV and at elevated ambient-pressure conditions on a single beamline. Another unique property of the beamline is that it reaches energies down to approximately 27 eV, which is not obtainable on other current APXPS beamlines. This allows, for instance, valence band studies under ambient-pressure conditions. In this article the main properties and performance of the beamline are presented, together with selected showcase experiments performed on the new setup.
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