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Highlights

  • Researchers have overcome the extreme challenge of directly observing the dynamics of how light excites electrons and generates electricity in solar cell and photovoltaic technologies.  The formation and dissociation of bound electron and hole pairs, known as excitons, were studied using a combination of broadband terahertz pulses (a trillion cycles per second) and selective laser pumping to reveal the light-induced excitation dynamics and charge transport mechanism within perovskites.  Perovskites are a class of materials that show promise as industrial solar energy materials...

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  • Temperature programmed surface reaction profiles of 2-propanol on CeO2 and Ce-Na for m/z=58.

    Researchers have discovered that sodium modification of ceria leads to boost in ceria catalytic activity for the formation of hydrogen from an alcohol that can be derived from renewable resources, isopropanol.  Infiltrating sodium carbonates into ceria disrupts its structure resulting in an increase in the number of surface oxygen vacancies.  This was shown using a combination of Raman spectroscopy, temperature programmed reactions spectroscopy, and chemisorption methods.  The distribution of sodium within the solid was investigated using 23Na solid-state nuclear...

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  • Bimodal coordination of methionine observed on alumina in the presence of a Pd catalyst using dynamic nuclear polarization surface-enhanced NMR spectroscopy.

    Researchers have discovered a core deactivation mechanism of noble metal catalysts that are used in biorefining and catalytic automobile converters.  Much like how physicians use X-ray and magnetic resonance (MRI) images to diagnose patients, X-ray absorption spectroscopy (XAS) and nuclear magnetic resonance spectroscopy (NMR) can be combined to diagnose the ‘ailments’ of the catalysts.  Using dynamic nuclear polarization (DNP) to enhance the NMR signals, the authors were able to measure the distances between carbon atoms in methionine, a compound known to be responsible for...

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  • Phase diagram of Ca(Fe1-xCox)2As2 in the free (black) and strained (red) state.

    By applying strain to iron-arsenide based superconductors, researchers were able to study the interplay between magnetic states, the tetragonal phase, the orthorhombic phase, and the onset of superconductivity of these materials. The Ca(Fe1-xCox)2As2 series is exceptionally pressure sensitive and crystals of these materials expand differently in each direction as temperature is applied. By rigidly adhering one side of the crystals to silica and taking advantage of the differences in their thermal expansion, in situ measurements of the...

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  • Schematic showing the probable location of the carbon dangling bonds via EPR and electronic measurements.

    Unattached, dangling carbon bonds have been shown experimentally to be the main culprit in degradation of polymer solar cells.  This type of solar cell has attracted intense attention due to their potential for use in flexible large-area, low-cost photovoltaic panels; degradation is the primary obstacle to commercialization.  Theoretical studies suggested photo-induced carbon-hydrogen bond rearrangement and breaking can lead to carbon dangling bonds and now this has been shown experimentally for the first time.  Researchers studied polymer:fullerene solar cells using the...

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  • BiI3 forms molecular complexes in solvents such as tetrahydrofuran or dimethylformamide, enabling solution-based deposition of thin films. Annealing BiI3 thin films in different solvents can dramatically change the morphology.  By annealing in dimethylformamide dense, large-grained films were produce that resulted in higher photocurrent and power conversion efficiency in proof-of-concept solar cells.

    Using inexpensive, solution-based processing, bismuth—halide (BiI3) thin films were produced and found to have optical properties that are suitable for solar energy harvesting.  While lead (Pb)-based halide perovskites have enormous promise for photovoltaic solar cells because of their low cost and high solar-to-electric power conversion efficiency, they also have poor stability and there are environmental and health concerns related to the high Pb content. BiI3 could be a more environmentally friendly alternative.  The researchers discovered that the...

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  • Salt-induced 2D hexagonal superlattices of polyethylene-glycol functionalize gold nanoparticles at the vapor-liquid interface.

    Researchers have developed a method to self-assemble close to perfect structures of gold nanoparticles.  The gold nanoparticles were grafted with polymer chains into 2D supercrystals by controlling salt concentration.  The materials were characterized using high-resolution synchrotron surface X-ray scattering methods, including grazing incidence small angle X-ray scattering and X-ray reflectivity, at the Advanced Photon Source, a U.S. Department of Energy, Office of Science User Facility.  At low salt concentrations, no ordered structures exist.  As salt concentration...

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  • Loci of the measured momentum dependence of the superconductor gap of the Fermi surface sheets.  The dashed line shows the expected variation of the gap based on a spin fluctuation model.   The significant deviation from predictions demonstrates the deficiency of current models.

    Measurements of the superconducting gap in a new member of the family of iron-based superconductors revealed substantial deviation from predictions of the well-established theory. In superconductors, electrons form Cooper pairs that behave like single particles. The force binding the electrons in pairs, known as the superconducting gap, often depends on the momentum of the electrons and its measurement shows fingerprints of the mechanism that causes superconductivity. Researchers used a technique known as laser angle-resolved photoemission spectroscopy combined with electronic structure...

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  • Cover art showing V. Smetana and A.-V. Mudring's work in Angewandte Chemie

    A double salt of cesium platinum and cesium hydride has been made for the first time. Simple salts, like sodium chloride, contain one positively charged element and one negatively charged element. This double salt contains two anions (Pt2- and H-) and one cation (Cs+). Einstein’s Theory of Relativity helps explain how this is possible. The average radial velocity of electrons closest to the nucleus is larger for heavier elements, which leads to a higher effective mass that then leads to a smaller than expected atomic radius, and changes in chemical...

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  • Constant energy intensity contour 10 meV above EF in the momentum space. White, gray and green are locations of the bands. points. Theoretically predicted locations for the Weyl points (green) and the experimentally determined points (red). Fermi arcs are seen as white strikes of intensity connecting “experimental” Weyl points.

    A new type of semimetal has been proven to exist in a crystal made of molybdenum and tellurium atoms.  In this recently postulated state, the electron and hole bands normally separated by a gap touch at a few discrete points, called Weyl points. The orientation of electron spin at those points in momentum space resembles magnetic field lines of magnetic monopoles. Weyl points are connected by “Fermi arcs” at the surface of the sample, which allow their identification.  Fermi arcs are disconnected, ungapped areas in density of states of these materials.  The proof of the...

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