Search

X-ray emission spectroscopy is emerging as an important complement to x-ray absorption fine structure spectroscopy, providing a characterization of the occupied electronic density of states local to the species of interest. Here, we present details of the design and performance of a compact x-ray emission spectrometer that uses a dispersive refocusing Rowland (DRR) circle geometry to achieve excellent performance for the 2-2.5 keV range, i.e., especially for the K-edge emission from sulfur and phosphorous. The DRR approach allows high energy resolution even for unfocused x-ray sources. This property enables high count rates in laboratory studies, approaching those of insertion-device beamlines at third-generation synchrotrons, despite use of only a low-powered, conventional x-ray tube. The spectrometer, whose overall scale is set by use of a 10-cm diameter Rowland circle and a new small-pixel complementary metal-oxide-semiconductor x-ray camera, is easily portable to synchrotron or x-ray free electron laser beamlines. Photometrics from measurements at the Advanced Light Source show excellent overall instrumental efficiency. In addition, the compact size of this instrument lends itself to future multiplexing to gain large factors in net collection efficiency or its implementation in controlled gas gloveboxes either in the lab or in an endstation.

Jiang and co-workers use high resolution STM to investigate the reaction and self-assembly of (3,6-dibromo-9,10-phenanthrenequinone, or DBPQ) molecules on Ag (100) and Ag (110) surfaces in order to understand the mechanism of bottom-up assembly on surfaces.[31] They show that, through the inclusion of multiple functional groups within a precursor molecule, it becomes possible to fabricate new low-dimensional materials with unique chemical, physical, and electronic properties. Herbst and Fransson consider the core-valence separation approximation that is often used in the calculation of core-level spectra.[5] They show how to quantify the errors in this approximation, thereby opening the door to error-quantified predictions relevant to x-ray spectroscopy. 153(16), 164108 (2020).10.1063/5.0019557 5 M. F. Herbst and T. Fransson, "Quantifying the error of the core-valence separation approximation", J. Chem. Phys. Zhu and co-workers tackle this problem for a model system containing a 2D semiconductor heterojunction and show convincingly the efficient hot electron transfer from photoexcited MoTe SB 2 sb to WS SB 2 sb .[30] This finding provides important insight into the competition between hot electron cooling and transfer at 2D semiconductor interfaces and suggests an intriguing possibility for the exploration of hot electron devices. [Extracted from the article]

As the commercial display market grows, the demand for low-toxicity, highly emissive, and size-tunable semiconducting nanoparticles has increased. Indium phosphide quantum dots represent a promising solution to these challenges; unfortunately, they typically suffer from low inherent emissivity resulting from charge carrier trapping. Strategies to improve the emissive characteristics of indium phosphide often involve zinc incorporation into or onto the core itself and the fabrication of core/shell heterostructures. InP clusters are high fidelity platforms for studying processes such as cation exchange and surface doping with exogenous ions since these clusters are used as single-source precursors for quantum dot synthesis. Here, we examined the incorporation of zinc and gallium ions in InP clusters and the use of the resultant doped clusters as single-source precursors to emissive heterostructured nanoparticles. Zinc ions were observed to readily react with InP clusters, resulting in partial cation exchange, whereas gallium resisted cluster incorporation. Zinc-doped clusters effectively converted to emissive nanoparticles, with quantum yields strongly correlated with zinc content. On the other hand, gallium-doped clusters failed to demonstrate improvements in quantum dot emission. These results indicate stark differences in the mechanisms associated with aliovalent and isovalent doping and provide insight into the use of doped clusters to make emissive quantum dots. [ABSTRACT FROM AUTHOR]

Several genome sequence analyses are conducted to explain the various mechanisms and features exhibited by Flavobacterium johnsoniae, a polysaccharide-digesting gliding bacterium. The numerous genes that are required for the formation of the outer membrane pigments in the bacterium are also identified.

Objectives/hypothesis: Patients with tracheostomies have an anatomically altered connection between their upper and lower airways that could impact SARS-CoV-2 testing. Our goal was to evaluate for discordance in SARS-CoV-2 detection in hospitalized patients with COVID-19 and tracheostomies based on the site analyzed.Study Design: Retrospective chart review METHODS: This single-institution study evaluated hospitalized patients with COVID-19 who had tracheostomies placed during their treatment. We analyzed SARS-CoV-2 RNA nucleic acid amplification test (NAAT) results after tracheostomy. All included patients had nasopharyngeal (NP) and tracheal (TR) samples taken within a 48-hour period, allowing us to characterize rate of test concordance.Results: Forty-five patients met our inclusion criteria. Thirty-two (71.1%) patients had entirely concordant results after tracheostomy. However, 13 (28.9%) patients had at least one set of discordant results, the majority of which were NP negative and TR positive. There were no statistically significant differences in demographic or clinical variables, including time to tracheostomy and time to testing, among patients with concordant versus discordant SARS-CoV-2 results.Conclusion: This represents the first study to examine SARS-CoV-2 RNA NAAT concordance between NP and TR sites in hospitalized patients with COVID-19 and tracheostomies. One-third of patients demonstrated discordant testing when NP and TR specimens were collected within a 48-hour time period. Thus, patients with tracheostomies may have a higher false-negative rate if only one site is assessed for SARS-CoV-2. We recommend analyzing samples from both the nasopharynx and trachea for these patients until more prospective data exist.Level Of Evidence: IV Laryngoscope, 2021. [ABSTRACT FROM AUTHOR]

Indium phosphide (InP) is the leading Cd‐free quantum dot material for application in photoluminescence downconversion display and lighting technologies. To date the performance of InP quantum dots (QDs) has lagged behind cadmium selenide in terms of both luminescence line width and quantum yield. Extensive studies in our lab have implicated kinetically persistent magic‐sized cluster intermediates as a leading contributor to polydispersity in these samples, providing new opportunities for achieving high color purity. Now, using a combination of solid‐state NMR spectroscopy and recently developed benchtop X‐ray emission spectroscopy, we have studied the evolution of oxidized phosphorus species during both synthesis and shell growth. [ABSTRACT FROM AUTHOR]

B Mengjie Yu b , University of Southern California, Los Angeles, CA, USA Dr. Mengjie Yu is Gabilan Assistant Professor of Electrical and Computer Engineering at University of Southern California (USC). B Mohammad-Ali Miri b , Queens College and the Graduate Center of the City University of New York, New York, NY, USA Dr. Mohammad-Ali Miri is an Assistant Professor of Physics at Queens College and the Graduate Center of the City University of New York. It is of vital importance to I APL Photonics i and the multidisciplinary photonics community to recognize excellence in early career researchers and to hear their perspectives. [Extracted from the article]

To that end, I APL Photonics i is pleased to announce our third annual cohort of Early Career Editorial Advisory Board members in this editorial. The Early Career Editorial Advisory Board appointees submitted applications to the selection committee, which was composed of members of the Editorial Advisory Board. [Extracted from the article]

As the commercial display market grows, the demand for low-toxicity, highly emissive, and size-tunable semiconducting nanoparticles has increased. Indium phosphide quantum dots represent a promising solution to these challenges; unfortunately, they typically suffer from low inherent emissivity resulting from charge carrier trapping. Strategies to improve the emissive characteristics of indium phosphide often involve zinc incorporation into or onto the core itself and the fabrication of core/shell heterostructures. InP clusters are high fidelity platforms for studying processes such as cation exchange and surface doping with exogenous ions since these clusters are used as single-source precursors for quantum dot synthesis. Here, we examined the incorporation of zinc and gallium ions in InP clusters and the use of the resultant doped clusters as single-source precursors to emissive heterostructured nanoparticles. Zinc ions were observed to readily react with InP clusters, resulting in partial cation exchange, whereas gallium resisted cluster incorporation. Zinc-doped clusters effectively converted to emissive nanoparticles, with quantum yields strongly correlated with zinc content. On the other hand, gallium-doped clusters failed to demonstrate improvements in quantum dot emission. These results indicate stark differences in the mechanisms associated with aliovalent and isovalent doping and provide insight into the use of doped clusters to make emissive quantum dots.

Recently the addition of M 2+ Lewis acids (M = Cd, Zn) to InP quantum dots (QDs) has been shown to enhance the photoluminescence quantum yield (PL QY). Here we investigate the stability of this Lewis acid layer to postsynthetic processing such as purification and ligand exchange. We utilize gel permeation chromatography to purify the quantum-dot samples as well as to aid in the ligand-exchange reactions. The Lewis-acid-capped particles are stable to purification and maintain the enhanced luminescence properties. We demonstrate successful ligand exchange on the quantum dots by switching the native carboxylate ligands to phosphonate ligands. Changes in the optical spectra after exposure to ambient environment indicate that both carboxylate- and phosphonate-capped QDs remain air-sensitive.

We demonstrate the ability of M(2+) Lewis acids (M = Cd, Zn) to dramatically enhance the photoluminescence quantum yield (PL QY) of InP quantum dots. The addition of cadmium and zinc is additionally found to red- and blue-shift, respectively, the lowest energy absorption and emission of InP quantum dots while maintaining particle size. This treatment results in a facile strategy to post-synthetically tune the luminescence color in these materials. Optical and structural characterization (XRD, TEM, XAS, ICP) have led us to identify the primary mechanism of PL turn-on as surface passivation of phosphorus dangling bonds, affording PL QYs up to 49% without the growth of a type I shell or the addition of HF. This route to PL enhancement and color tuning may prove useful as a standalone treatment or as a complement to shelling strategies.