We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV-9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.

We report on the photon energy dependence of the K-shell double photoionization (DPI) of Mg, Al, and Si. The DPI cross sections were derived from high-resolution measurements of x-ray spectra following the radiative decay of the K-shell double vacancy states. Our data evince the relative importance of the final-state electron-electron interaction to the DPI. By comparing the double-to-single K-shell photoionization cross-section ratios for neutral atoms with convergent close-coupling calculations for He-like ions, the effect of outer shell electrons on the K-shell DPI process is assessed. Universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms is revealed.

X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.

We report on the decomposition of platinum acetylacetonate (Pt(acac)(2)) in hydrogen induced by flash heating. The changes in the local Pt structure were followed by high energy resolution off-resonant spectroscopy uniquely performed with sub-second time resolution. The decomposition consists of a two-step reduction process of the Pt(II) species.

Single-photon double K-shell ionization of low-Z neutral atoms in the range 12 Z 23 is investigated. The experimental method was based on measurements of the high-resolution Kα h hypersatellite x-ray spectra following the radiative decay of the K-shell double-vacancy states excited by monochromatic synchrotron radiation. The photon energy dependence of the double K-shell ionization was measured over a wide range of photon energies from threshold up to and beyond the maximum of the double-to-single photoionization cross section ratios. From the high-resolution x-ray emission spectra the energies and linewidths of the hypersatellite transitions, as well as the Kα h 1 :Kα h 2 intensity ratios, were determined. The relative importance of the initialstate and final-state electron-electron interactions to the K-shell double photoionization is addressed. Physical mechanisms and scaling laws of the K-shell double photoionization are examined. A semiempirical universal scaling of the double-photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2 Z 47 is established.

X-ray emission spectra recorded in the off-resonant regime carry information on the density of unoccupied states. It is known that by employing the Kramers-Heisenberg formalism, the high energy resolution off-resonant spectroscopy (HEROS) is equivalent to the x-ray absorption spectroscopy (XAS) technique and provides the same electronic state information. Moreover, in the present Letter we demonstrate that the shape of HEROS spectra is not modified by self-absorption effects. Therefore, in contrast to the fluorescence-based XAS techniques, the recorded shape of the spectra is independent of the sample concentration or thickness. The HEROS may thus be used as an experimental technique when precise information about specific absorption features and their strengths is crucial for chemical speciation or theoretical evaluation. DOI: 10.1103/PhysRevLett.112.173003 PACS numbers: 32.30.Rj, 31.15.ag, 32.70.Jz, 32.80.Fb The high-intensity and highly monochromatic x-ray radiation available at synchrotron sources allow researchers from different disciplines to study the local electronic and geometric structure of materials by means of x-ray absorption spectroscopy (XAS). To record a XAS spectrum the x-ray energy is tuned around the electron binding energy of the element of interest, thereby exciting electrons from one of the core levels to unoccupied states or into the continuum. The photo-absorption process depends on the photon energy and is a measure of the material's absorption coefficient which in turn provides information on the material properties. The energy region around the absorption edge, namely the x-ray absorption near edge structure (XANES), reflects the density of empty states [1]. The region starting about 100 eV above the absorption edge is called the extended x-ray absorption fine structure (EXAFS) region, and the analysis of this region yields information on the local geometric structure [2].X-ray absorption spectra can be measured in the transmission, fluorescence, and electron-yield mode [3,4]. In the transmission mode, the XAS spectra are measured by recording the intensity of the photon beam before and after the sample. The fluorescence mode involves the use of x-ray emission spectroscopy (XES) techniques allowing detection of the fluorescence yield as a function of the incident photon energy. The XAS spectrum can be obtained from either the total fluorescence yield (TFY) or the partial fluorescence yield (PFY) measurements. In TFY the fluorescence intensity is integrated over a broad emission energy range, while in the PFY it is integrated over a selected emission energy range. In particular, the fluorescence yield integrated over an energy band centered at a given fluorescence line and narrower than the natural linewidth of the latter is referred to as the high energy resolution XAS [5,6]. It provides more detailed information about absorption features and allows precise chemical speciation [7].The field of x-ray absorption spectroscopy is a very important tool in the fields of physics, chemist...

Using 98% linearly polarized radiation at the European Synchrotron Radiation Facility in Grenoble, the performance of a prototype two-dimensional microstrip Ge(i) detector for x-ray imaging and as a Compton polarimeter has been evaluated. Using the energy and position sensitivity of the detector, the ability to obtain a complete reconstruction of the Compton event has been demonstrated. The modulation coefficient of the polarimeter is in good agreement with the theoretical limit of a perfect detector.

In this work two synchrotron radiation-based depth-sensitive X-ray fluorescence techniques, grazing incidence X-ray fluorescence (GIXRF) and grazing emission X-ray fluorescence (GEXRF), are compared and their potential for non-destructive depth-profiling applications is investigated. The depth-profiling capabilities of the two methods are illustrated for five aluminum-implanted silicon wafers all having the same implantation dose of 10 16 atoms per cm 2 but with different implantation energies ranging from 1 keV up to 50 keV. The work was motivated by the ongoing downscaling effort of the microelectronics industry and the resulting need for more sensitive methods for the impurity and dopant depth-profile control. The principles of GIXRF and GEXRF, both based on the refraction of X-rays at the sample surface to enhance the surface-to-bulk ratio of the detected fluorescence signal, are explained. The complementary experimental setups employed at the Physikalisch-Technische Bundesanstalt (PTB) for GIXRF and the University of Fribourg for GEXRF are presented in detail. In particular, for each technique it is shown how the dopant depth profile can be derived from the angular intensity dependence of the Al Ka fluorescence line. The results are compared to theoretical predictions and, for two samples, crosschecked with values obtained from secondary ion mass spectroscopy (SIMS) measurements. A good agreement between the different approaches is found proving that the GIXRF and GEXRF methods can be efficiently employed to extract the dopant depth distribution of ionimplanted samples with good accuracy and over a wide range of implantation energies.