Use Of X-ray Emission Spectroscopy Research Articles

Probing Sulfur Chemical and Electronic Structure with Experimental Observation and Quantitative Theoretical Prediction of Kα and Valence-to-Core Kβ X-ray Emission Spectroscopy.

An extensive experimental and theoretical study of the Kα and Kβ high-resolution X-ray emission spectroscopy (XES) of sulfur-bearing systems is presented. This study encompasses a wide range of organic and inorganic compounds, including numerous experimental spectra from both prior published work and new measurements. Employing a linear-response time-dependent density functional theory (LR-TDDFT) approach, strong quantitative agreement is found in the calculation of energy shifts of the core-to-core Kα as well as the full range of spectral features in the valence-to-core Kβ spectrum. The ability to accurately calculate the sulfur Kα energy shift supports the use of sulfur Kα XES as a bulk-sensitive tool for assessing sulfur speciation. The fine structure of the sulfur Kβ spectrum, in conjunction with the theoretical results, is shown to be sensitive to the local electronic structure including effects of symmetry, ligand type and number, and, in the case of organosulfur compounds, to the nature of the bonded organic moiety. This agreement between theory and experiment, augmented by the potential for high-access XES measurements with the latest generation of laboratory-based spectrometers, demonstrates the possibility of broad analytical use of XES for sulfur and nearby third-row elements. The effective solution of the forward problem, i.e., successful prediction of detailed spectra from known molecular structure, also suggests future use of supervised machine learning approaches to experimental inference, as has seen recent interest for interpretation of X-ray absorption near-edge structure (XANES).

High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential.

X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a soft X-ray synchrotron beamline to perform emission spectroscopy with good chemical sensitivity over a very wide range of energies.

Determination of Chemical Valence State by X-ray Emission Analysis Using Electron Beam Instruments: Pitfalls and Promises

The use of X-ray emission spectroscopy to determine the valence states of first-row transition elements is evaluated using measurements of X-ray wavelength shifts, line shapes, and relative X-ray line intensities (Lβ/Lα and Kβ/ Kα). X-ray wavelength (or energy) centroids and line shapes are shown to vary not only with oxidation state but also with chemical bonding for the same oxidation state. In many of the cases studied, the ratio of Kβ to Ka is shown to vary depending upon the differential absorption at a similar level to what is cited in the literature as due to the valence state. Similarly, in a number of cases studied, the ratio of Lβ to Lα is shown to vary by differences in self-absorption (and at low electron beam energies, differences in overvoltage) by levels comparable to what is ascribed in the literature as due to valence state. Differences were found among compounds with different oxidation states that exceeded the magnitude predicted by absorption or overvoltage effects; however, no systematic variations were found that were dependent only on the valence state of the element (as opposed to which other elements it was bonded). The results show that oxidation state cannot be simply and unambiguously determined by X-ray emission spectroscopy at the resolution obtainable with conventional wavelength-dispersive detectors on electron microscopes or microprobes. Of the various techniques employed in X-ray emission spectroscopy, the most promising for oxidation-state determination appears to be measurement of the wavelength shift and/or satellite line shape variation, but then only when comparing compounds in which the cation has the same bonding environment. It is critically important to correct for self-absorption effects when attempting to relate variations in Lβ/Lα to differences in oxidation state or bonding environment, regardless of the electron beam energy used in analysis. Specifically, Lβ/Lα measurements cannot be used to determine the oxidation state of Cu in high-temperature superconductors.

Analysis of fly ash by X-ray emission spectroscopy and proton microbeam analysis

The use of X-ray emission spectroscopy for the study of properties of fly-ash particles is reported where different techniques of sample excitation were used. The elemental composition of bulk ash was obtained by exposing the samples to radiation from radioactive sources, X-ray tube and synchrotron radiation. Proton microbeam was used to measure the concentration profiles of different elements in individual ash particles.

Angle-dependent x-ray sulfurK-emission bands and electronic structure ofSnS2andMoS2

The angular dependence of polarized S $K$-emission bands of ${\mathrm{SnS}}_{2}$ and ${\mathrm{MoS}}_{2}$ was studied with the use of x-ray emission spectroscopy (XES). By application of the self-consistent pseudopotential method, the band structure, the local partial densities of states, and the x-ray bands were calculated. Good agreement between experiment and theory has been observed. The $s$,$p$,$d$ character and localization of valence electrons are identified, and the shape of spectra is fully explained. The particular role of $d$-like electrons in the Mo---S bond and the Mo $L{\ensuremath{\beta}}_{2}$-emission bands is discussed. The relations between core states, valence states, and polarization of radiation are analyzed. The results are compared with available XES, and x-ray and ultraviolet photoelectron spectroscopy measurements.

Use of x-ray emission spectroscopy in the characterization of thin films of aluminum oxides and hydroxides

X-ray emission bands (AlK β) of several aluminum oxides and hydroxides have been compared. The bands from the oxyhydroxides and γ-Al 2O 3 are single peaks with some variations in peak position from material to material. However, the band from α-Al 2O 3 is much broader and forms a distinct doublet. The bands from the oxyhydroxides occur at shorter wavelengths than the peaks from α-Al 2O 3. These results may be used to aid in the characterization of thin films (crystalline as well as non-crystalline) on aluminum and aluminum alloys.