We have broadened the scope of the aminophosphine precursor chemistry that has been developed for InP quantum dots to the synthesis of cadmium, zinc, cobalt, and nickel phosphide nanocrystals. The generalized synthetic conditions involve thermolysis of the appropriate MX 2 salt with tris-diethylaminophosphine in a long chain primary amine. The resulting Cd 3 P 2 nanocrystals exhibit size tuning effects based on the metal halide reactivity. 31 P NMR studies show that the II-V materials form via the previously described mechanism observed for InP, demonstrating the invariance of this chemistry to the metal valence. We also demonstrate that electrocatalytically active transition metal phosphides, specifically Co 2 P, CoP, and Ni 2 P, can be produced using this synthetic method at relatively mild temperatures and in high yields.
X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced xray spectroscopies that impact a wide range of disciplines. However, unlike the majority of other spectroscopic methods, XAFS and XES are accompanied by an unusual access model, wherein; the dominant use of the technique is for premier research studies at world-class facilities, i.e., synchrotron x-ray light sources. In this paper we report the design and performance of an improved spectrometer XAFS and XES based on the general conceptual design of Seidler, et al., Rev. Sci. Instrum. 2014. New developments include reduced mechanical degrees of freedom, much-increased flux, and a wider Bragg angle range to enable extended x-ray absorption fine structure (EXAFS) for the first time with this type of modern laboratory XAFS configuration. This instrument enables a new class of routine applications that are incompatible with the mission and access model of the synchrotron light sources. To illustrate this, we provide numerous examples of x-ray absorption near edge structure (XANES), EXAFS, and XES results for a variety of problems and energy ranges. Highlights include XAFS and XES measurements of battery electrode materials, EXAFS of Ni and V with full modeling of results to validate monochromator performance, valence-to-core XES for 3d transition metal compounds, and uranium XANES and XES for different oxidation states. Taken en masse, these results further support the growing perspective that modern laboratory-based XAFS and XES have the potential to develop a new branch of analytical chemistry.
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).
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