Nitrides feature many interesting properties, such as a wide range of bandgaps suitable for optoelectronic devices including light-emitting diodes (LEDs), and piezoelectric response used in ...microelectromechanical systems (MEMS). Nitrides are also significantly underexplored compared to oxides and other chemistries, with many being thermochemically metastable, sparking interest from a basic science point of view. This paper reports on experimental and computational exploration of the Mg–Sb–N material system, featuring both metastable materials and semiconducting properties. Using sputter deposition, we discovered a new Mg2SbN3 nitride with a wurtzite-derived crystal structure and synthesized the antimonide-nitride Mg3SbN with an antiperovskite crystal structure for the first time in thin film form. Theoretical calculations indicate that Mg2SbN3 is metastable and has properties relevant to LEDs and MEMS, whereas Mg3SbN has a large dielectric constant (28ε0) and low hole effective masses (0.9m 0), of interest for photovoltaic solar cell absorbers. The experimental solar-matched 1.3 eV optical absorption onset of the Mg3SbN antiperovskite agrees with the theoretical prediction (1.3 eV direct, 1.1 eV indirect), and with the measurements of room-temperature near-bandgap photoluminescence. These results make an important contribution toward understanding semiconductor properties and chemical trends in the Mg–Sb–N materials system, paving the way to future practical applications of these novel materials.
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Changing energy Perkins, John H
2017., 20170912, 2017, 2017-09-01
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Changing Energy outlines how humanity established the current energy economy through three previous transitions, and how we now stand poised for a necessary fourth transition. Human societies around ...the globe have received immense benefits from uses of coal, oil, gas, and uranium sources, yet we must now rebuild our energy economies to rely on renewable sources and use them efficiently. The imperative for a fourth energy transition comes from dangers related to climate change, geopolitical tensions, documented health and environmental effects, and long-term depletion of today’s sources. John H. Perkins argues that a future in which current levels of energy service benefits are sustained can come only from investments in the technologies needed to bring about a fourth energy transition. Changing Energy envisions a viable post–fossil fuel economy and identifies the barriers to be overcome.
Skin and soft tissue infections are common emergency department (ED) presentations. These infections cover a wide spectrum of disease, from simple cellulitis to necrotizing fasciitis. Despite the ...commonality, a subset of skin and soft tissue infections known as necrotizing soft tissue infections (NSTIs) can cause significant morbidity and mortality.
This review evaluates the current evidence regarding the presentation, evaluation, and management of NSTI from the ED perspective.
NSTIs are commonly missed diagnoses. History and physical examination findings are inconsistent, and the risk factors for this high mortality disease are common amongst ED populations. Laboratory evaluation and the Laboratory Risk in Necrotizing Fasciitis (LRINEC) score is helpful but is insufficient to rule out the disease. Imaging modalities including ultrasound, computed tomography, and magnetic resonance imaging are highly sensitive and specific, but may delay definitive management. The gold standard for diagnosis includes surgical exploration. Surgical intervention and empiric broad-spectrum antibiotic coverage are the foundations of treatment. Adjuvant therapies including hyperbaric oxygen and intravenous immunoglobulin have not yet been proven to be beneficial or to improve outcome.
NSTIs are associated with significant morbidity and mortality. Knowledge of the history, examination, evaluation, and management is vital for emergency clinicians.
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Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optical and electronic devices. In contrast, rocksalt-structured nitrides are known for their superconducting ...and refractory properties. Breaking this dichotomy, herewe report ternary nitride semiconductors with rocksalt crystal structures, remarkable electronic properties, and the general chemical formula MgₓTM
1−xN (TM = Ti, Zr, Hf, Nb). Our experiments show that these materials form over a broad metal composition range, and that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8 to 2.1 eV) and up to 100 cm² V−1·s−1 electron mobility for MgZrN₂ grown on MgO substrates. Complementary ab initio calculations reveal that these materials have disorder-tunable optical absorption, large dielectric constants, and electronic bandgaps that are relatively insensitive to disorder. These ternary MgₓTM
1−xN semiconductors are also structurally compatible both with binary TMN superconductors and main-group nitride semiconductors along certain crystallographic orientations. Overall, these results highlight MgₓTM
1−xN as a class of materials combining the semiconducting properties of main-group wurtzite nitrides and rocksalt structure of superconducting transition-metal nitrides.
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Methylammonium lead halide (MAPbX3) perovskites exhibit exceptional carrier transport properties. But their commercial deployment as solar absorbers is currently limited by their intrinsic ...instability in the presence of humidity and their lead content. Guided by our theoretical predictions, we explored the potential of methylammonium bismuth iodide (MBI) as a solar absorber through detailed materials characterization. We synthesized phase‐pure MBI by solution and vapor processing. In contrast to MAPbX3, MBI is air stable, forming a surface layer that does not increase the recombination rate. We found that MBI luminesces at room temperature, with the vapor‐processed films exhibiting superior photoluminescence (PL) decay times that are promising for photovoltaic applications. The thermodynamic, electronic, and structural features of MBI that are amenable to these properties are also present in other hybrid ternary bismuth halide compounds. Through MBI, we demonstrate a lead‐free and stable alternative to MAPbX3 that has a similar electronic structure and nanosecond lifetimes.
Call me MA‐Bi‐I! A lead‐free alternative to hybrid lead perovskites is explored for solar cells: methylammonium bismuth iodide (see figure). This material exhibits higher air stability than hybrid lead perovskites, while demonstrating optoelectronic properties promising for solar absorbers.
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The use of advanced machine learning algorithms in experimental materials science is limited by the lack of sufficiently large and diverse datasets amenable to data mining. If publicly open, such ...data resources would also enable materials research by scientists without access to expensive experimental equipment. Here, we report on our progress towards a publicly open High Throughput Experimental Materials (HTEM) Database (htem.nrel.gov). This database currently contains 140,000 sample entries, characterized by structural (100,000), synthetic (80,000), chemical (70,000), and optoelectronic (50,000) properties of inorganic thin film materials, grouped in >4,000 sample entries across >100 materials systems; more than a half of these data are publicly available. This article shows how the HTEM database may enable scientists to explore materials by browsing web-based user interface and an application programming interface. This paper also describes a HTE approach to generating materials data, and discusses the laboratory information management system (LIMS), that underpin HTEM database. Finally, this manuscript illustrates how advanced machine learning algorithms can be adopted to materials science problems using this open data resource.
We report on the theoretical prediction and experimental realization of new ternary zinc molybdenum nitride compounds. We used theory to identify previously unknown ternary compounds in the Zn–Mo–N ...systems, Zn3MoN4 and ZnMoN2, and to analyze their bonding environment. Experiments show that Zn–Mo–N alloys can form in broad composition range from Zn3MoN4 to ZnMoN2 in the wurtzite-derived structure, accommodating very large off-stoichiometry. Interestingly, the measured wurtzite-derived structure of the alloys is metastable for the ZnMoN2 stoichiometry, in contrast to the Zn3MoN4 stoichiometry, where ordered wurtzite is predicted to be the ground state. The formation of Zn3MoN4–ZnMoN2 alloy with wurtzite-derived crystal structure is enabled by the concomitant ability of Mo to change oxidation state from +VI in Zn3MoN4 to +IV in ZnMoN2, and the capability of Zn to contribute to the bonding states of both compounds, an effect that we define as “redox-mediated stabilization”. The stabilization of Mo in both the +VI and +IV oxidation states is due to the intermediate electronegativity of Zn, which enables significant polar covalent bonding in both Zn3MoN4 and ZnMoN2 compounds. The smooth change in the Mo oxidation state between Zn3MoN4 and ZnMoN2 stoichiometries leads to a continuous change in optoelectronic propertiesfrom resistive and semitransparent Zn3MoN4 to conductive and absorptive ZnMoN2. The reported redox-mediated stabilization in zinc molybdenum nitrides suggests there might be many undiscovered ternary compounds with one metal having an intermediate electronegativity, enabling significant covalent bonding, and another metal capable of accommodating multiple oxidation states, enabling stoichiometric flexibility.
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Transparent conductors (TCs) combine the usually contraindicated properties of electrical conductivity with optical transparency and are generally made by starting with a transparent insulator and ...making it conductive via heavy doping, an approach that generally faces severe "doping bottlenecks." We propose a different idea for TC design-starting with a metallic conductor and designing transparency by control of intrinsic interband transitions and intraband plasmonic frequency. We identify the specific design principles for three such prototypical intrinsic TC classes and then search computationally for materials that satisfy them. Remarkably, one of the intrinsic TC, Ag(3)Al(22)O(34), is predicted also to be a prototype 3D compounds that manifest natural 2D electron gas regions with very high electron density and conductivity.
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