We present a multicrystal Johann-type hard x-ray spectrometer (∼5–18 keV) recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The instrument is set at the wiggler beamline 6-2 equipped with two liquid nitrogen cooled monochromators – Si(111) and Si(311) – as well as collimating and focusing optics. The spectrometer consists of seven spherically bent crystal analyzers placed on intersecting vertical Rowland circles of 1 m of diameter. The spectrometer is scanned vertically capturing an extended backscattering Bragg angular range (88°–74°) while maintaining all crystals on the Rowland circle trace. The instrument operates in atmospheric pressure by means of a helium bag and when all the seven crystals are used (100 mm of projected diameter each), has a solid angle of about 0.45% of 4π sr. The typical resolving power is in the order of \documentclass[12pt]{minimal}\begin{document}$\frac{E}{\Delta E} \sim 10\,000$\end{document}EΔE∼10000. The spectrometer's high detection efficiency combined with the beamline 6-2 characteristics permits routine studies of x-ray emission, high energy resolution fluorescence detected x-ray absorption and resonant inelastic x-ray scattering of very diluted samples as well as implementation of demanding in situ environments.

Sulfur's balancing act in cytochrome c: Cytochrome c enzymes have two distinct functions that depend on the position of a methionine residue. When the sulfur in the methionine side chain coordinates with iron in the enzyme's active site, the protein is optimized for electron transfer; otherwise, it is poised for peroxidase activity. Mara et al. used ultrafast x-ray absorption and emission spectroscopy to probe the energetics of this Fe-S bond (see the Perspective by Bren and Raven). By breaking the bond transiently with light and then timing its reformation, they determined that the surrounding protein environment boosts the bond strength by 4 kilocalories per mole—just enough to toggle between each functional state at a practical rate. Science , this issue p. 1276 ; see also p. 1236

Monolayer MoS₂ is a promising semiconductor to overcome the physical dimension limits of microelectronic devices. Understanding the thermochemical stability of MoS₂ is essential since these devices generate heat and are susceptible to oxidative environments. Herein, the promoting effect of molybdenum oxides (MoO_x) particles on the thermal oxidation of MoS₂ monolayers is shown by employing operando X‐ray absorption spectroscopy, ex situ scanning electron microscopy and X‐ray photoelectron spectroscopy. The study demonstrates that chemical vapor deposition‐grown MoS₂ monolayers contain intrinsic MoO_x and are quickly oxidized at 100 °C (3 vol% O₂/He), in contrast to previously reported oxidation thresholds (e.g., 250 °C, t ≤ 1 h in the air). Otherwise, removing MoO_x increases the thermal oxidation onset temperature of monolayer MoS₂ to 300 °C. These results indicate that MoO_x promote oxidation. An oxide‐free lattice is critical to the long‐term stability of monolayer MoS₂ in state‐of‐the‐art 2D electronic, optical, and catalytic applications.

We present a new x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station is located at wiggler beamline 6-2 equipped with two monochromators-Si(111) and Si(311) as well as collimating and focusing optics. It consists of two multi-crystal Johann type spectrometers arranged on intersecting Rowland circles of 1 m diameter. The first one, positioned at the forward scattering angles (low-q), consists of 40 spherically bent and diced Si(110) crystals with 100 mm diameters providing about 1.9% of 4π sr solid angle of detection. When operated in the (440) order in combination with the Si (311) monochromator, an overall energy resolution of 270 meV is obtained at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers (not diced), is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. The solid angle of this spectrometer is about 0.9% of 4π sr, with a combined energy resolution of 600 meV using the Si (311) monochromator. These features exceed the specifications of currently existing relevant instrumentation, opening new opportunities for the routine application of this photon-in/photon-out hard x-ray technique to emerging research in multidisciplinary scientific fields, such as energy-related sciences, material sciences, physical chemistry, etc.