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"A half-wave rectified alternating current electrochemical method for uranium extraction from seawater" — Chong Liu: Po-Chun Hsu, Jin Xie, Jie Zhao, Tong Wu, Haotian Wang, Wei Liu, Jinsong Zhang, Steven Chu and Yi Cui; Nature Energy, 02/17/17.
In total there is hundreds of times more uranium in sea water than on land, but extracting it for use in nuclear power generation is challenging due to its low concentration (∼3 ppb) and the high salinity background. Current approaches based on sorbent materials are limited due to their surface-based physicochemical adsorption nature. Here we use a half-wave rectified alternating current electrochemical (HW-ACE) method for uranium extraction from sea water based on an amidoximefunctionalized carbon electrode. The amidoxime functionalization enables surface specific binding to uranyl ions, while the electric field can migrate the ions to the electrode and induce electrodeposition of uranium compounds, forming charge-neutral species. Extraction is not limited by the electrode surface area, and the alternating manner of the applied voltage prevents unwanted cations from blocking the active sites and avoids water splitting. The HW-ACE method achieved a ninefold higher uranium extraction capacity (1,932 mg g−1 ) without saturation and fourfold faster kinetics than conventional physicochemical methods using uranium-spiked sea water
"Ubiquitous strong electron–phonon coupling at the interface of FeSe/SrTiO3" — Chaofan Zhang: Zhongkai Liu, Zhuoyu Chen, Yanwu Xie, Ruihua He, Shujie Tang, Junfeng He, Wei Li, Tao Jia, Slavko N. Rebec, Eric Yue Ma, Hao Yan, Makoto Hashimoto, Donghui Lu, Sung-Kwan Mo, Yasuyuki Hikita, Robert G. Moore, Harold Y. Hwang, Dunghai Lee & Zhixun Shen; Nature Communications, 02/10/17.
The observation of replica bands in single-unit-cell FeSe on SrTiO3(STO)(001) by angle-resolved photoemission spectroscopy (ARPES) has led to the conjecture that the coupling between FeSe electrons and the STO phonons are responsible for the enhancement of Tc over other FeSe-based superconductors. However the recent observation of a similar superconducting gap in single-unit-cell FeSe/STO(110) raised the question of whether a similar mechanism applies. Here we report the ARPES study of the electronic structure of FeSe/STO(110). Similar to the results in FeSe/STO(001), clear replica bands are observed. We also present a comparative study of STO(001) and STO(110) bare surfaces, and observe similar replica bands separated by approximately the same energy, indicating this coupling is a generic feature of the STO surfaces and interfaces. Our findings suggest that the large superconducting gaps observed in FeSe films grown on different STO surface terminations are likely enhanced by a common mechanism.
"Coexistence of Replica Bands and Superconductivity in FeSe Monolayer Films" — S. N. Rebec: T. Jia, C. Zhang, M. Hashimoto, D.-H. Lu, R. G. Moore, and Z.-X. Shen; Physical Review Letters, 02/10/17.
To elucidate the mechanisms behind the enhanced Tc in monolayer (1 ML) FeSe on SrTiO3 (STO), we grew highly strained 1 ML FeSe on the rectangular (100) face of rutile TiO2, and observed the coexistence of replica bands and superconductivity with a Tc of 63 K. From the similar Tc between this system and 1ML FeSe on STO (001), we conclude that strain and dielectric constant are likely unimportant to the enhanced Tc in these systems. A systematic comparison of 1 ML FeSe on TiO2 with other systems in the FeSe family shows that while charge transfer alone can enhance Tc, it is only with the addition of interfacial electron-phonon coupling that Tc can be increased to the level seen in 1 ML FeSe on STO.
"Sulﬁphilic Nickel Phosphosulﬁde Enabled Li2S Impregnation in 3D Graphene Cages for Li–S Batteries" — Guangmin Zhou: Jie Sun, Yang Jin, Wei Chen, Chenxi Zu, Rufan Zhang, Yongcai Qiu, Jie Zhao, Denys Zhuo, Yayuan Liu, Xinyong Tao, Wei Liu, Kai Yan, Hye Ryoung Lee, and Yi Cui; Advanced Materials, 01/30/17.
A 3D graphene cage with a thin layer of electrodeposited nickel phosphosulfide for Li2S impregnation, using ternary nickel phosphosulphide as a highly conductive coating layer for stabilized polysulfide chemistry, is accomplished by the combination of theoretical and experimental studies. The 3D interconnected graphene cage structure leads to high capacity, good rate capability and excellent cycling stability in a Li2S cathode.
"Modular soft x-ray spectrometer for applications in energy sciences and quantum materials" — Yi-De Chuang: Yu-Cheng Shao, Alejandro Cruz, Kelly Hanzel, Adam Brown, Alex Frano, Ruimin Qiao, Brian Smith, Edward Domning, Shih-Wen Huang, L. Andrew Wray, Wei-Sheng Lee, Zhi-Xun Shen, Thomas P. Devereaux, Jaw-Wern Chiou, Way-Faung Pong, Valeriy V. Yashchuk, Eric Gullikson, Ruben Reininger, Wanli Yang, Jinghua Guo, Robert Duarte, and Zahid Hussain; Review of Scientific Instruments, 01/27/17.
Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components. The spectrometer’s optics chamber can be used with gratings operated in either inside or outside orders, and the detector assembly can be reconfigured accordingly. The spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving power when using small source (∼1 µm) and detector pixels (∼5 µm) with high line density gratings (∼3000 lines/mm), or high throughput at moderate resolution. We report two such spectrometers with slightly different design goals and optical parameters in this paper. We show that the spectrometer with high throughput and large energy window is particularly useful for studying the sustainable energy materials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery cathode material LiNi1/3Co1/3Mn1/3O2 can be produced in few hours using such a spectrometer. Unlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the elemental absorption edges to determine various spectral features like the localized dd excitations and non-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying such RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes hard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this modular spectrometer design can serve as the platform for further customization to meet specific scientific demands.
"High-pressure behavior of A2B2O7 pyrochlore (A=Eu, Dy; B=Ti, Zr)" — Dylan R. Rittman: Katlyn M. Turner, Sulgiye Park, Antonio F. Fuentes, Jinyuan Yan, Rodney C.Ewing, and Wendy L. Mao; Journal of Applied Physics , 01/24/17.
In situ high-pressure X-ray diffraction and Raman spectroscopy were used to determine the influence of composition on the high-pressure behavior of A2B2O7 pyrochlore (A = Eu, Dy; B = Ti, Zr) up to ∼ 50 GPa. Based on X-ray diffraction results, all compositions transformed to the high-pressure cotunnite structure. The B-site cation species had a larger effect on the transition pressure than the A-site cation species, with the onset of the phase transformation occurring at ∼ 41 GPa for B = Ti and ∼ 16 GPa B = Zr. However, the A-site cation affected the kinetics of the phase transformation, with the transformation for compositions with the smaller ionic radii, i.e., A = Dy, proceeding faster than those with a larger ionic radii, i.e., A = Eu. These results were consistent with previous work in which the radius-ratio of the A- and B-site cations determined the energetics of disordering, and compositions with more similarly sized A- and B-site cations had a lower defect formation energy. Raman spectra revealed differences in the degree of short-range order of the different compositions. Due to the large phase fraction of cotunnite at high pressure for B = Zr compositions, Raman modes for cotunnite could be observed, with more modes recorded for A = Eu than A =Dy. These additional modes are attributed to increased short-to-medium range ordering in the initially pyrochlore structured Eu2Zr2O7 as compared with the initially defect-fluorite structured Dy2Zr2O7.
"Ultrafast light-induced symmetry changes in single BaTiO3 nanowires" — Yi-Hong Kuo: Sanghee Nah, Kai He, Te Hu, Aaron M. Lindenberg; Journal of Materials Chemistry C, 01/23/17.
The coupling of light to nanoscale ferroelectric materials enables novel means of controlling their coupled degrees of freedom and engineering new functionality. Here we present femtosecond time-resolution nonlinear-optical measurements of light-induced dynamics within single ferroelectric barium titanate nanowires. By analyzing the time-dependent and polarization-dependent second harmonic intensity generated by the nanowire, we identify its crystallographic orientation and then make use of this information in order to probe its dynamic structural response and change in symmetry. We show that photo-excitation leads to ultrafast, non-uniform modulations in the second order nonlinear susceptibility tensor, indicative of changes in the local symmetry of the nanostructure occurring on sub-picosecond time-scales.
"Hybrid metal–organic chalcogenide nanowires with electrically conductive inorganic core through diamondoid-directed assembly" — Hao Yan: J. Nathan Hohman, Fei Hua Li, Chunjing Jia, Diego Solis-Ibarra, Bin Wu, Jeremy E. P. Dahl, Robert M. K. Carlson, Boryslav A. Tkachenko, Andrey A. Fokin, Peter R. Schreiner, Arturas Vailionis, Taeho Roy Kim, Thomas P. Devereaux, Zhi-Xun Shen & Nicholas A. Melosh; Nature Materials, 12/26/16.
Controlling inorganic structure and dimensionality through structure-directing agents is a versatile approach for new materials synthesis that has been used extensively for metal–organic frameworks and coordination polymers. However, the lack of ‘solid’ inorganic cores requires charge transport through single-atom chains and/or organic groups, limiting their electronic properties. Here, we report that strongly interacting diamondoid structure-directing agents guide the growth of hybrid metal–organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. The strong van der Waals attraction between diamondoids overcomes steric repulsion leading to a cis configuration at the active growth front, enabling face-on addition of precursors for nanowire elongation. These nanowires have band-like electronic properties, low effective carrier masses and three orders-of-magnitude conductivity modulation by hole doping. This discovery highlights a previously unexplored regime of structure-directing agents compared with traditional surfactant, block copolymer or metal–organic framework linkers.
"Distinct Electronic Structure for the Extreme Magnetoresistance in YSb" — Junfeng He: Chaofan Zhang, Nirmal J. Ghimire, Tian Liang, Chunjing Jia, Juan Jiang, Shujie Tang, Sudi Chen, Yu He, S.-K. Mo, C. C. Hwang, M. Hashimoto, D. H. Lu, B. Moritz, T. P. Devereaux, Y. L. Chen, J. F. Mitchell, and Z.-X. Shen; Physical Review Letters, 12/23/16.
An extreme magnetoresistance (XMR) has recently been observed in several nonmagnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb.
"Ideal charge-density-wave order in the high-field state of superconducting YBCO" — H. Jang: W.-S. Lee, H. Nojiri, S. Matsuzawa, H. Yasumura, L. Nie, A. V. Maharaj, S. Gerber, Y.-J. Liu, A. Mehta, D. A. Bonn, R. Liang, W. N. Hardy, C. A. Burns, Z. Islam, S. Song, J. Hastings, T. P. Devereaux, Z.-X. Shen, S. A. Kivelson, C.-C. Kao, D. Zhu, and J.-S. Lee; Proceedings of the National Academy of Sciences, 12/20/16.
The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.