L-Edge Spectroscopy of Dilute, Radiation-Sensitive Systems Using a Transition-Edge-Sensor Array

We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by conventional grating-based spectrometers. These results show that soft X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples.Comment: 19 pages, 4 figure

Design study of a photon beamline for a soft X-ray FEL driven by high gradient acceleration at EuPRAXIA@SPARC_LAB

We are proposing a facility based on high gradient acceleration via x-band RF structures and plasma acceleration. We plan to reach an electron energy of the order of 1 GeV, suitable to drive a Free Electron Laser for applications in the so called "water window" (2 - 4 nm). A conceptual design of the beamline, from the photon beam from the undulators to the user experimental chamber, mainly focusing on diagnostic, manipulation and transport of the radiation is presented and discussed. We also briefly outline a user end station for coherent imaging, laser ablation and pump-probe experiments

Biological niches within human calcified aortic valves. Towards understanding of the pathological biomineralization process

Despite recent advances, mineralization site, its microarchitecture, and composition in calcific heart valve remain poorly understood. A multiscale investigation, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS), from micrometre up to nanometre, was conducted on human severely calcified aortic and mitral valves, to provide new insights into calcificationp rocess. Our aim was to evaluate the spatial relationship existing between bioapatite crystals, their local growing microenvironment, and the presence of a hierarchical architecture. Here we detected the presence of bioapatite crystals in two different mineralization sites that suggest the action of two different growth processes:a pathological crystallization process that occurs in biological niches and is ascribed to a purely physicochemical process and a matrix- mediated mineralized process in which the extracellular matrix acts as the template for a site-directed nanocrystals nucleation. Different shapes of bioapatite crystallization were observed at micrometer scale in each microenvironment but at the nanoscale level crystals appear to be made up by the same subunit

A design of resonant inelastic X-ray scattering (RIXS) spectrometer for spatial- and time-resolved spectroscopy.

The optical design of a Hettrick-Underwood-style soft X-ray spectrometer with Wolter type 1 mirrors is presented. The spectrometer with a nominal length of 3.1 m can achieve a high resolving power (resolving power higher than 10000) in the soft X-ray regime when a small source beam (<3 µm in the grating dispersion direction) and small pixel detector (5 µm effective pixel size) are used. Adding Wolter mirrors to the spectrometer before its dispersive elements can realize the spatial imaging capability, which finds applications in the spectroscopic studies of spatially dependent electronic structures in tandem catalysts, heterostructures, etc. In the pump-probe experiments where the pump beam perturbs the materials followed by the time-delayed probe beam to reveal the transient evolution of electronic structures, the imaging capability of the Wolter mirrors can offer the pixel-equivalent femtosecond time delay between the pump and probe beams when their wavefronts are not collinear. In combination with some special sample handing systems, such as liquid jets and droplets, the imaging capability can also be used to study the time-dependent electronic structure of chemical transformation spanning multiple time domains from microseconds to nanoseconds. The proposed Wolter mirrors can also be adopted to the existing soft X-ray spectrometers that use the Hettrick-Underwood optical scheme, expanding their capabilities in materials research

Investigating the Liquid State of Carbon

Carbon materials have a many contemporary applications and new carbon allotropes are being discovered. However, while graphite and diamond are well understood, very little is known about the liquid state of carbon due to the high temperatures (above 5,000 K) and pressures (above 10 MPa) required for its formation. Initial studies used electrical heating to determine the melting point of graphite and the resistivity of liquid carbon. More recent studies used non-thermal laser melting to generate a metastable liquid that was studied with visible reflectivity and X-ray spectroscopies. Shock waves have also been used to transiently generate liquid carbon. Theoretical calculations of liquid carbon initially suggested the possibility of a liquid-liquid phase transition, but later ab initio quantum mechanical simulations showed only a continuous change in liquid coordination as its density increased. In this dissertation, extreme-UV (EUV) reflectivity and chirped coherent anti-Stokes Raman spectroscopy (c-CARS) were used to study non-thermally melted liquid carbon. Femtosecond laser pulses at 250 nm with a fluence of 0.45 J/cm2 (3.5 x 1012 W/cm2 intensity) were used to generate liquid carbon from an amorphous carbon substrate and the time evolution of EUV reflectivity was probed. EUV wavelengths from 20 to 42 nm were used with both s and p polarizations. The reflectivity decreased at all wavelengths probed as the material expanded and ablated. For wavelengths below 32 nm, the reflectivity decay time was less than ~2 ps. This time constant describes the lattice dynamics after melting, while above 32 nm, the reflectivity is also sensitive to the hot electron plasma generated by the melting pulse. From these results and equations for the behavior of a shock wave in a material, the electron temperature of the melted material was found to be 0.30 ± 0.6 eV. The reflectivity at two different polarizations was also used to calculate the complex refractive index of the material as it evolved over time. C-CARS spectra were obtained for highly ordered pyrolytic graphite (HOPG) and glassy carbon using CARS pump wavelengths of 400 nm and 800 nm. These spectra showed strong G peak resonance (1580 cm-1), corresponding to the relative vibrations of sp2 carbons in the material. The D peak (~1350 cm-1) resonance seen in Raman scattering of disordered graphite films was not observed in the CARS spectra. As this mode occurs when the excited electron scatters from a defect or phonon, it could be that the stimulated Stokes emission that occurs during the CARS process prevents such scattering. The sample was melted with an 800 nm, 90 fs laser pulse with fluences from 0.40 to 0.85 J/cm2 (intensities of 4.4 x 1012 to 9.4 x 1012 W/cm2). Delay times of less than 500 fs and as long as 100 ps all showed no broadening or shifting of the G peak, as would be expected for damaging and disordering of the material; only an intensity change is seen as the material ablates. Microscope images show permanent damage to the substrate and the fluences and times studied were comparable to those used in published reflectivity studies of liquid carbon. To advance the study of liquid carbon, a soft X-ray second harmonic generation (SHG) technique was developed and explored. X-ray absorption provides element-specific information on the electronic structure of a material that is sensitive to the environment around the element. Combining this with the interface specificity of SHG, provides a useful technique for studying solid-solid interfaces that are difficult to study otherwise. Our first soft X-ray SHG experiments on graphite films showed that the technique was indeed highly interface specific. The technique was also sensitive to resonance amplification when the input photons were at or above the carbon K-edge. A second experiment compared the boron/vacuum interface to a buried boron/carbon (Parylene-N) interface. The technique was sensitive to interface effects, showing larger SHG intensity at the boron K-edge for the boron/Parylene-N interface compared to the boron/vacuum interface. Ab initio quantum simulations were used to calculate the soft X-ray SHG spectra of these systems, verifying the interface sensitivity of the technique

Quantitative Biological Electron Probe Microanalysis with a Wavelength Dispersive Spectrometer

This paper describes the details of quantitative electron probe microanalysis (EPMA) performed with a wavelength dispersive spectrometer (WDS). EPMA was carried out on the giant neuron of a fresh frozen ganglion from the snail Lymnaea stagnalis. The freeze-dried cryosections were compared with sections of freeze-dried, embedded tissue. It was found, that in the ganglion there are two kinds of neurons with a different chlorine concentration of 11 mmole/liter and 32 mmole/liter. Isolated neurons in culture were shown to differ in elemental composition from those in the ganglion tissue

Report of the Terrestrial Bodies Science Working Group. Volume 5: Mars

Present knowledge of the global properties and surface characteraretics of Mars and the composition and dynamics of its atmosphere are reviewed. The objectives of proposed missions, the exploration strategy, and supporting research and technology required are delineated

Stochastic stimulated electronic x-ray Raman spectroscopy

Resonant inelastic x-ray scattering (RIXS) is a well-established tool for studying electronic, nuclear and collective dynamics of excited atoms, molecules and solids. An extension of this powerful method to a time-resolved probe technique at x-ray free electron lasers (XFELs) to ultimately unravel ultrafast chemical and structural changes on a femtosecond time scale is often challenging, due to the small signal rate in conventional implementations at XFELs that rely on the usage of a monochromator set up to select a small frequency band of the broadband, spectrally incoherent XFEL radiation. Here, we suggest an alternative approach, based on stochastic spectroscopy, that uses the full bandwidth of the incoming XFEL pulses. Our proposed method is relying on stimulated resonant inelastic x-ray scattering, where in addition to a pump pulse that resonantly excites the system a probe pulse on a specific electronic inelastic transition is provided, that serves as seed in the stimulated scattering process. The limited spectral coherence of the XFEL radiation defines the energy resolution in this process and stimulated RIXS spectra of high resolution can be obtained by covariance analysis of the transmitted spectra. We present a detailed feasibility study and predict signal strengths for realistic XFEL parameters for the CO molecule resonantly pumped at the O1s-{\pi}* transition. Our theoretical model describes the evolution of the spectral and temporal characteristics of the transmitted x-ray radiation, by solving the equation of motion for the electronic and vibrational degrees of freedom of the system self consistently with the propagation by Maxwell's equations