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1. Crystal structures of two bis-carbamoylmethylphosphine oxide (CMPO) compounds

   https://doi.org/10.1107/S205698901900820X  

   VanderWeide, Andrew I. ; Staples, Richard J. ; Biros, Shannon M. ( July 2019 , Acta Crystallographica Section E Crystallographic Communications)

   Two bis-carbamoylmethylphosphine oxide compounds, namely {[(3-{[2-(diphenylphosphinoyl)ethanamido]methyl}benzyl)carbamoyl]methyl}diphenylphosphine oxide, C 36 H 34 N 2 O 4 P 2 , (I), and diethyl [({2-[2-(diethoxyphosphinoyl)ethanamido]ethyl}carbamoyl)methyl]phosphonate, C 14 H 30 N 2 O 8 P 2 , (II), were synthesized via nucleophilic acyl substitution reactions between an ester and a primary amine. Hydrogen-bonding interactions are present in both crystals, but these interactions are intramolecular in the case of compound (I) and intermolecular in compound (II). Intramolecular π–π stacking interactions are also present in the crystal of compound (I) with a centroid–centroid distance of 3.9479 (12) Å and a dihedral angle of 9.56 (12)°. Intermolecular C—H...π interactions [C...centroid distance of 3.622 (2) Å, C—H...centroid angle of 146°] give rise to supramolecular sheets that lie in the ab plane. Key geometric features for compound (I) involve a nearly planar, trans- amide group with a C—N—C—C torsion angle of 169.12 (17)°, and a torsion angle of −108.39 (15)° between the phosphine oxide phosphorus atom and the amide nitrogen atom. For compound (II), the electron density corresponding to the phosphoryl group was disordered, and was modeled as two parts with a 0.7387 (19):0.2613 (19) occupancy ratio. Compound (II) also boasts a trans -amide group that approaches planarity with a C—N—C—C torsion angle of −176.50 (16)°. The hydrogen bondsmore »in this structure are intermolecular, with a D ... A distance of 2.883 (2) Å and a D —H... A angle of 175.0 (18)° between the amide hydrogen atom and the P=O oxygen atom. These non-covalent interactions create ribbons that run along the b -axis direction.« less
2. Substitutional transition metal doping in MoS ₂ : a first-principles study

   https://doi.org/10.1088/2632-959X/ab7cb3  

   Yoshimura, Anthony ; Koratkar, Nikhil ; Meunier, Vincent ( March 2020 , Nano Express)

   Single-layer MoS₂is a direct-gap semiconductor whose band edges character is dominated by the d-orbitals of the Mo atoms. It follows that substitutional doping of the Mo atoms has a significant impact on the material’s electronic properties, namely the size of the band gap and the position of the Fermi level. Here, density functional theory is used along with the G₀W₀method to examine the effects of substituting Mo with four different transition metal dopants: Nb, Tc, Ta, and Re. Nb and Ta possess one less valence electron than Mo does and are therefore p-type dopants, while Re and Tc are n-type dopants, having one more valence electron than Mo has. Four types of substitutional structures are considered for each dopant species: isolated atoms, lines, three-atom clusters centered on a S atom (c3s), and three-atom clusters centered on a hole (c3h). The c3h structure is found to be the most stable configuration for all dopant species. However, electronic structure calculations reveal that isolated dopants are preferable for efficient n- or p-type performance. Lastly, it is shown that photoluminescence measurements can provide valuable insight into the atomic structure of the doped material. Understanding these properties of substitutionally-doped MoS₂can allow for its successfulmore »implementation into cutting-edge solid state devices.

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3. Mechanistic Studies of the Electrocatalytic Carbon–Bromine Cleavage and the Hydrogen Atom Incorporation from 1,1,1,3,3,3-Hexaflouroisopropanol

   https://doi.org/10.1149/1945-7111/aca126  

   Rudman, Kelly K. ; Thapa, Bishnu ; Tapash, Arifuzzaman ; Mubarak, Mohammad S. ; Raghavachari, Krishnan ; Hosseini, Seyyedamirhossein ; Minteer, Shelley D. ( November 2022 , Journal of The Electrochemical Society)

   Electrochemical dehalogenation of polyhalogenated compounds is an inefficient process as the working electrode is passivated by the deposition of short-chain polymers that form during the early stages of electrolysis. Herein, we report the use of 1, 1, 1, 3, 3, 3-hexaflouroisopropanol (HFIP) as an efficient reagent to control C–H formation over the radical association. Debromination of 1,6-dibromohexane was examined in the presence of Ni(II) salen and HFIP as the electrocatalyst and hydrogen atom source, respectively. Electrolysis of 10 mM 1,6-dibromohexane and 2 mM Ni(II) salen in the absence of HFIP yields 50% unreacted 1,6-dibromohexane and ∼40% unaccounted for starting material, whereas electrolysis with 50 mM HFIP affords 65%n-hexane. The mechanism of hydrogen atom incorporation was examined via deuterium incorporation coupled with high-resolution mass spectrometry, and density functional theory (DFT) calculations. Deuterium incorporation analysis revealed that the hydrogen atom originated from the secondary carbon of HFIP. DFT calculations showed that the deprotonation of hydroxyl moiety of HFIP, prior to the hydrogen atom transfer, is a key step for C–H formation. The scope of electrochemical dehalogenation was examined by electrolysis of 10 halogenated compounds. Our results indicate that through the use of HFIP, the formation of short-chain polymers is no longer observed,more »and monomer formation is the dominant product.

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4. Gravitational caustics in an atom laser

   https://doi.org/10.1038/s41467-021-27555-3  

   Mossman, M. E. ; Bersano, T. M. ; Forbes, Michael McNeil ; Engels, P. ( December 2021 , Nature Communications)

   Typically discussed in the context of optics, caustics are envelopes of classical trajectories (rays) where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns. Here, we generate caustics in the matter waves of an atom laser, providing a striking experimental example of catastrophe theory applied to atom optics in an accelerated (gravitational) reference frame. We showcase caustics formed by individual attractive and repulsive potentials, and present an example of a network generated by multiple potentials. Exploiting internal atomic states, we demonstrate fluid-flow tracing as another tool of this flexible experimental platform. The effective gravity experienced by the atoms can be tuned with magnetic gradients, forming caustics analogous to those produced by gravitational lensing. From a more applied point of view, atom optics affords perspectives for metrology, atom interferometry, and nanofabrication. Caustics in this context may lead to quantum innovations as they are an inherently robust way of manipulating matter waves.
5. Multi-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination

   https://doi.org/10.1038/s41535-020-00303-4  

   Sharma, Rahul ; Kreisel, Andreas ; Sulangi, Miguel Antonio ; Böker, Jakob ; Kostin, Andrey ; Allan, Milan P. ; Eisaki, H. ; Böhmer, Anna E. ; Canfield, Paul C. ; Eremin, Ilya ; et al ( January 2021 , npj Quantum Materials)

   Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$, for all momentakon the Fermi surface of every bandα. While there are a variety of techniques for determining$$|{\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha |$$$\mid {\Delta }_k^{\alpha }\mid$, no general method existed to measure the signed values of$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$. Recently, however, a technique based on phase-resolved visualization of superconducting quasiparticle interference (QPI) patterns, centered on a single non-magnetic impurity atom, was introduced. In principle, energy-resolved and phase-resolved Fourier analysis of these images identifies wavevectors connecting allk-space regions where$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$has the same or opposite sign. But use of a single isolated impurity atom, from whose precise location the spatial phase of the scattering interference pattern must be measured, is technically difficult. Here we introduce a generalization of this approach for use with multiple impurity atoms, and demonstrate its validity by comparing the$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$it generates to the$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$determined from single-atom scattering in FeSe where s_±energy-gap symmetry is established. Finally, to exemplify utility, we use the multi-atom technique on LiFeAs and find scattering interference between the hole-like and electron-like pockets as predicted for$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$${\Delta }_k^{\alpha }$of opposite sign.