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Enhanced photovoltage for inverted planar heterojunction perovskite solar cells (2018)

Luo, D., Yang, W., Wang, Z., Sadhanala, A., Hu, Q., Su, R., Shivanna, R., Trindade, G. F., Watts, J. F., Xu, Z., Liu, T., Chen, K., Ye, F., Wu, P., Zhao, L., Wu, J., Tu, Y., Zhang, Y., Yang, X., Zhang, W., Friend, R. H., Gong, Q., Snaith, H. J., Zhu, R.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-06-29

Beschreibung: The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages ( V oc ). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in V oc by up to 100 millivolts. We achieved a high V oc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Schlagwort(e): Materials Science, Physics

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Revealing hidden spin-momentum locking in a high-temperature cuprate superconductor (2018)

Gotlieb, K., Lin, C.-Y., Serbyn, M., Zhang, W., Smallwood, C. L., Jozwiak, C., Eisaki, H., Hussain, Z., Vishwanath, A., Lanzara, A.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-12-14

Beschreibung: Cuprate superconductors have long been thought of as having strong electronic correlations but negligible spin-orbit coupling. Using spin- and angle-resolved photoemission spectroscopy, we discovered that one of the most studied cuprate superconductors, Bi2212, has a nontrivial spin texture with a spin-momentum locking that circles the Brillouin zone center and a spin-layer locking that allows states of opposite spin to be localized in different parts of the unit cell. Our findings pose challenges for the vast majority of models of cuprates, such as the Hubbard model and its variants, where spin-orbit interaction has been mostly neglected, and open the intriguing question of how the high-temperature superconducting state emerges in the presence of this nontrivial spin texture.

Schlagwort(e): Materials Science, Physics

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Ultralarge elastic deformation of nanoscale diamond (2018)

Banerjee, A., Bernoulli, D., Zhang, H., Yuen, M.-F., Liu, J., Dong, J., Ding, F., Lu, J., Dao, M., Zhang, W., Lu, Y., Suresh, S.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-04-20

Beschreibung: Diamonds have substantial hardness and durability, but attempting to deform diamonds usually results in brittle fracture. We demonstrate ultralarge, fully reversible elastic deformation of nanoscale (~300 nanometers) single-crystalline and polycrystalline diamond needles. For single-crystalline diamond, the maximum tensile strains (up to 9%) approached the theoretical elastic limit, and the corresponding maximum tensile stress reached ~89 to 98 gigapascals. After combining systematic computational simulations and characterization of pre- and postdeformation structural features, we ascribe the concurrent high strength and large elastic strain to the paucity of defects in the small-volume diamond nanoneedles and to the relatively smooth surfaces compared with those of microscale and larger specimens. The discovery offers the potential for new applications through optimized design of diamond nanostructure, geometry, elastic strains, and physical properties.

Schlagwort(e): Engineering, Materials Science

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Maternal Huluwa dictates the embryonic body axis through {beta}-catenin in vertebrates (2018)

Yan, L., Chen, J., Zhu, X., Sun, J., Wu, X., Shen, W., Zhang, W., Tao, Q., Meng, A.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-11-23

Beschreibung: The vertebrate body is formed by cell movements and shape change during embryogenesis. It remains undetermined which maternal signals govern the formation of the dorsal organizer and the body axis. We found that maternal depletion of huluwa , a previously unnamed gene, causes loss of the dorsal organizer, the head, and the body axis in zebrafish and Xenopus embryos. Huluwa protein is found on the plasma membrane of blastomeres in the future dorsal region in early zebrafish blastulas. Huluwa has strong dorsalizing and secondary axis–inducing activities, which require β-catenin but can function independent of Wnt ligand/receptor signaling. Mechanistically, Huluwa binds to and promotes the tankyrase-mediated degradation of Axin. Therefore, maternal Huluwa is an essential determinant of the dorsal organizer and body axis in vertebrate embryos.

Schlagwort(e): Development, Genetics, Online Only

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Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Controlling guest conformation for efficient purification of butadiene (2017)

Liao, P.-Q., Huang, N.-Y., Zhang, W.-X., Zhang, J.-P., Chen, X.-M.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2017-06-16

Beschreibung: Conventional adsorbents preferentially adsorb the small, high-polarity, and unsaturated 1,3-butadiene molecule over the other C 4 hydrocarbons from which it must be separated. We show from single-crystal x-ray diffraction and computational simulation that a hydrophilic metal-organic framework, [Zn 2 (btm) 2 ], where H 2 btm is bis(5-methyl-1 H -1,2,4-triazol-3-yl)methane, has quasi-discrete pores that can induce conformational changes in the flexible guest molecules, weakening 1,3-butadiene adsorption through a large bending energy penalty. In a breakthrough operation at ambient temperature and pressure, this guest conformation–controlling adsorbent eluted 1,3-butadiene first, then butane, butene, and isobutene. Thus, 1,3-butadiene can be efficiently purified (≥99.5%) while avoiding high-temperature conditions that can lead to its undesirable polymerization.

Schlagwort(e): Materials Science

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Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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A Fermi-degenerate three-dimensional optical lattice clock (2017)

Campbell, S. L., Hutson, R. B., Marti, G. E., Goban, A., Darkwah Oppong, N., McNally, R. L., Sonderhouse, L., Robinson, J. M., Zhang, W., Bloom, B. J., Ye, J.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2017-10-06

Beschreibung: Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 x 10 17 . Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 x 10 –19 in 1 hour of averaging time.

Schlagwort(e): Physics

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Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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7

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Enantioselective cyanation of benzylic C-H bonds via copper-catalyzed radical relay (2016)

Zhang, W., Wang, F., McCann, S. D., Wang, D., Chen, P., Stahl, S. S., Liu, G.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2016-09-02

Beschreibung: Direct methods for stereoselective functionalization of sp 3 -hybridized carbon–hydrogen [C(sp 3 )–H] bonds in complex organic molecules could facilitate much more efficient preparation of therapeutics and agrochemicals. Here, we report a copper-catalyzed radical relay pathway for enantioselective conversion of benzylic C–H bonds into benzylic nitriles. Hydrogen-atom abstraction affords an achiral benzylic radical that undergoes asymmetric C(sp 3 )–CN bond formation upon reaction with a chiral copper catalyst. The reactions proceed efficiently at room temperature with the benzylic substrate as limiting reagent, exhibit broad substrate scope with high enantioselectivity (typically 90 to 99% enantiomeric excess), and afford products that are key precursors to important bioactive molecules. Mechanistic studies provide evidence for diffusible organic radicals and highlight the difference between these reactions and C–H oxidations mediated by enzymes and other catalysts that operate via radical rebound pathways.

Schlagwort(e): Chemistry

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Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Ultrafast electro-optic light with subcycle control (2018)

Carlson, D. R., Hickstein, D. D., Zhang, W., Metcalf, A. J., Quinlan, F., Diddams, S. A., Papp, S. B.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-09-28

Beschreibung: Light sources that are ultrafast and ultrastable enable applications like timing with subfemtosecond precision and control of quantum and classical systems. Mode-locked lasers have often given access to this regime, by using their high pulse energies. We demonstrate an adaptable method for ultrastable control of low-energy femtosecond pulses based on common electro-optic modulation of a continuous-wave laser light source. We show that we can obtain 100-picojoule pulse trains at rates up to 30 gigahertz and demonstrate sub–optical cycle timing precision and useful output spectra spanning the near infrared. Our source enters the few-cycle ultrafast regime without mode locking, and its high speed provides access to nonlinear measurements and rapid transients.

Schlagwort(e): Physics

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Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing (2017)

Rao, F., Ding, K., Zhou, Y., Zheng, Y., Xia, M., Lv, S., Song, Z., Feng, S., Ronneberger, I., Mazzarello, R., Zhang, W., Ma, E.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2017-12-15

Beschreibung: Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge 2 Sb 2 Te 5 ). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc 0.2 Sb 2 Te 3 ) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.

Schlagwort(e): Physics, Applied

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Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Can we beat influenza? (2017)

Zhang, W., Webster, R. G.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2017-07-14

Schlagwort(e): Editorials

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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