Catálogo de publicaciones - revistas

<jats:title>Lighting a route for hyperbolic dispersion</jats:title> <jats:p> The propagation of light within a material is usually well defined, with the propagation described by scattering and dispersion. In artificially designed metamaterials and in anisotropic layered materials, the dispersion can be hyperbolic, giving rise to subwavelength confinement of the light. Sternbach <jats:italic>et al.</jats:italic> show that the hyperbolic dispersion can be optically switched on and off on demand in the layered transition metal dichalcogenide tungsten diselenide (see the Perspective by Deng and Chen). Illuminating the material with ultrafast pulses of sub-bandgap light creates a transient waveguide, resulting in hyperbolic dispersion in the material. The ability to tune the dispersion characteristics on demand using optical pumping is an effective approach for developing ultrafast switching photonic devices and controlling the propagation of light on the nanoscale. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="617" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abe9163">617</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="572" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abf7933">572</jats:related-article> </jats:p>

<jats:title>Double C–H amination</jats:title> <jats:p>The conversion of C–H bonds into C–N bonds is broadly useful in producing pharmaceutically important compounds from simple, readily available feedstocks. Shen and Lambert report a method to induce this reaction twice in a row at benzylic and neighboring alkyl carbon centers, using acetonitrile solvent as a convenient source of nitrogen. The method relies on successive electrochemical and photochemical activation of a cyclopropenium catalyst and yields hydrogen gas as a clean co-product.</jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="620" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abf2798">620</jats:related-article> </jats:p>

<jats:title>Solvents forming redox mediators</jats:title> <jats:p> The role of solvents participating directly in thermal catalytic reactions is clearer for homogeneous catalysis than for heterogeneous catalysis. Adams <jats:italic>et al.</jats:italic> studied the formation of hydrogen peroxide from hydrogen and oxygen on palladium nanoparticles by measuring the kinetic isotope effect and performing density functional theory simulations in aqueous and organic solvents. Methanol formed chemisorbed hydroxymethyl intermediates. These surface redox mediators transferred electrons and protons to adsorbed oxygen species and were regenerated by oxidizing chemisorbed hydrogen atoms. However, water molecules heterolytically oxidized hydrogen to generate solvated protons and surface electrons that reduced oxygen. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="626" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abc1339">626</jats:related-article> </jats:p>

<jats:title>Microhabitat matters</jats:title> <jats:p> Understanding how our warming climate affects vulnerable species is of paramount importance. However, predicting responses is complicated because species are complex and may adapt or respond in distinct ways. Riddell <jats:italic>et al.</jats:italic> compared a century-old dataset on species richness in the Mojave against modern surveys to measure climate-related changes in bird and small mammal communities. They found little change in mammal richness or occupancy but large declines across birds. They attribute these differences to differences in microclimate opportunities: Specifically, mammals can mitigate temperature impacts through burrowing, whereas birds are generally more exposed. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="633" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abd4605">633</jats:related-article> </jats:p>

<jats:title>A-sites join the band edge</jats:title> <jats:p> The band edge of hybrid organic-inorganic perovskites, which have the general formula ABX <jats:sub>3</jats:sub> , is mainly controlled by the inorganic X anions (such as chloride) and the B cation (such as lead). Organic A-site cations usually only exert indirect structural effects because their electronic levels lie far from the band edge. Xue <jats:italic>et al.</jats:italic> show that cations with large π-conjugated structures can interact with inorganic frontier molecular orbitals. A surface layer of ethylammonium pyrene, which had an optimal intercalation distance, increased hole mobilities and power conversion efficiencies relative to a reference inorganic perovskite and also improved device stability. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6529" page="636" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abd4860">636</jats:related-article> </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>