Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userExplaining the x-ray nonlinear susceptibility of diamond and silicon near absorption edges
99
0
0.0
(
0
)
Added by
Bernardo Barbiellini
Publication date
2015
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We report the observation and the theoretical explanation of the parametric down-conversion nonlinear susceptibility at the $K$-absorption edge of diamond and at the $L_{23}$-absorption edge of a silicon crystal. Using arguments similar to those invoked to successfully predict resonant inelastic x-ray spectra, we derive an expression for the renormalization term of the non-linear susceptibility at the x-ray edges, which can be evaluated by using first-principles calculations of the atomic scattering factor $f_1$. Our model is shown to reproduce the observed enhancement of the parametric down-conversion at the diamond $K$ and the Si $L_{23}$ edges rather than the suppression previously claimed.
rate research
Read More
We study resonant inelastic x-ray scattering (RIXS) peaks corresponding to low energy particle-hole excited states of metallic FeTe and semi-metallic TiSe$_2$ for photon incident energy tuned near the $L_{3}$ absorption edge of Fe and Ti respectively. We show that the cross section amplitudes are well described within a renormalization group theory where the effect of the core electrons is captured by effective dielectric functions expressed in terms of the the atomic scattering parameters $f_1$ of Fe and Ti. This method can be used to extract the dynamical structure factor from experimental RIXS spectra in metallic systems.
We report the near-edge x-ray absorption fine structure (NEXAFS) spectrum of a single layer of graphite (graphene) obtained by micromechanical cleavage of Highly Ordered Pyrolytic Graphite (HOPG) on a SiO2 substrate. We utilized a PhotoEmission Electron Microscope (PEEM) to separately study single- double- and few-layers graphene (FLG) samples. In single-layer graphene we observe a splitting of the pi* resonance and a clear signature of the predicted interlayer state. The NEXAFS data illustrate the rapid evolution of the electronic structure with the increased number of layers.
Time-dependent and constituent-specific spectral changes in soft near edge X-ray spectroscopy (XAS) of an [Fe/MgO]$_8$ metal/insulator heterostructure upon laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining X-ray absorption spectroscopy with ultrafast electron diffraction measurements and ab initio calculations demonstrate that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near edge XAS to phonons is demonstrated.
We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low poer x-ray (bremsstrahlung) tube source, a spherically-bent crystal analyzer (SBCA), and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of 5 keV to 10 keV while also dmeonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy (XES) comparable to those achived at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure (XANES), the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-powered line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10^6 to 10^7 photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.
The structural, electronic and optical properties of cubic double perovskite BaCoWO6 have been studied. Neutron powder diffraction data is collected on this sample from 6K to 300K. The crystal structure is face centered cubic, space group being Fm3m (No. 225). We did not find evidence for long range magnetic ordering in this system in this temperature range. The band-gap is estimated using Uv-vis spectroscopy. The Co-K edge X-ray absorption (XAFS) spectra of Ba2CoWO6 was analysed together with those Co-foil, which was used as reference compounds. X-ray photoemission spectroscopy (XPS), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies give the insight of the electronic and structural information on the Co local environment for Ba2CoWO6.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
