Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition

Polaritons with directional in-plane propagation and ultralow losses in van der Waals (vdW) crystals promise unprecedented manipulation of light at the nanoscale. However, these polaritons present a crucial limitation: their directional propagation is intrinsically determined by the crystal structure of the host material, imposing forbidden directions of propagation. Here, we demonstrate that directional polaritons (in-plane hyperbolic phonon polaritons) in a vdW crystal (α-phase molybdenum trioxide) can be directed along forbidden directions by inducing an optical topological transition, which emerges when the slab is placed on a substrate with a given negative permittivity (4H–silicon carbide). By visualizing the transition in real space, we observe exotic polaritonic states between mutually orthogonal hyperbolic regimes, which unveil the topological origin of the transition: a gap opening in the dispersion. This work provides insights into optical topological transitions in vdW crystals, which introduce a route to direct light at the nanoscale.

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Canalization acoustic phonon polaritons in metal-MoO3-metal sandwiched structures for nano-light guiding and manipulation

Journal of Optics ◽

10.1088/2040-8986/ac4319 ◽

2021 ◽

Author(s):

Qizhi Yan ◽

Runkun Chen ◽

Zhu Yuan ◽

Peining Li ◽

Xinliang Zhang

Keyword(s):

Electromagnetic Field ◽

Double Layer ◽

Layered Structure ◽

Acoustic Phonon ◽

Molybdenum Trioxide ◽

Electromagnetic Mode ◽

Α Phase ◽

Phonon Polaritons ◽

Metal Layers

Abstract We theoretically propose and study in-plane anisotropic acoustic phonon polaritons (APhPs) based on a layered structure consisting of a monolayer (or few layers) α-phase molybdenum trioxide (α-MoO3) sandwiched between two metal layers. We find that the APhPs in the proposed sandwiched structures are a canalization (highly directional) electromagnetic mode propagating along with the layers and at the same time exhibit extreme electromagnetic-field confinement surpassing any other type of phonon-polariton modes. When a double layer of α-MoO3 is sandwiched by two Au layers, twisting the two α-MoO3 layers can adjust the interlayer polaritonic coupling and thus manipulate the in-plane propagation of the highly confined APhPs. Our results illustrate that the metal-MoO3-metal sandwiched structures are a promising platform for light guiding and manipulation at ultimate scale.

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SINTESIS DAN KARAKTERISASI NANOFIBER KOMPOSIT Zn-PVDF KOPOLIMER

Jurnal Kimia Terapan Indonesia ◽

10.14203/jkti.v16i1.1 ◽

2014 ◽

Vol 16 (1) ◽

pp. 49-52

Author(s):

Yelfira Sari ◽

Muhamad Nasir ◽

Chandra Risdian ◽

Syukri Syukri

Keyword(s):

Crystal Structure ◽

Phase Structure ◽

Research Study ◽

Fiber Diameter ◽

Average Diameter ◽

Nanofiber Composite ◽

Β Phase ◽

Α Phase ◽

Structure Morphology ◽

Electrospinning Method

Sintesis nanofiber komposit Zn-PVDF kopolimer dengan metoda elektrospinning telah berhasil dilakukan. Proses pembuatan nanofiber komposit serta morfologi yang terbentuk dipengaruhi oleh penambahan Zn-asetat dengan perubahan diameter rata-rata serat dari 357,13 nm menjadi 777,24 nm. Analisis FTIR menunjukkan bahwa struktur kristal nanofiber komposit Zn-PVDF kopolimer didominasi oleh strukturβ-phase, dengan bilangan gelombang 1190,08 cm-1 dan 487,99 cm-1 untuk struktur α-phase dan 1404,18 cm-1; 1280,73 cm-1; 1074,35 cm-1; 881,47 cm-1; dan 840,96 cm-1 untuk struktur β-phase.Kata kunci :nanofiber komposit, Zn-PVDF kopolimer komposit, elektrospinning,kristal struktur, morfologi, diameter fiber The fabrication of Zn-PVDF copolymer nanofiber composite has been investigated in this research study by using electrospinning method. Fabrication and morphology of nanofiber composite is influenced by the addition of Zn-acetate. The average diameter of nanofiber composites increase with an addition of Zn-acetate, from 357,13 to 777,24nm. FTIRanalysisshowedthat thecrystalstructure ofPVDFnanofiberis dominatedby β-phase , thewave number 1190,08 cm-1 and 487,99 cm-1 for α-phase structure and 1404,18cm-1; 1280,73cm-1; 1074,35cm-1; 881,47cm-1and840,96cm-1 for β-phase structure respectively.Key words : nanofiber composite, Zn-PVDF copolymer composite, electrospinning, crystal structure, morphology, fiber diameter

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From space to superspace and back: Superspace Group Finder

Journal of Applied Crystallography ◽

10.1107/s0021889808034390 ◽

2008 ◽

Vol 41 (6) ◽

pp. 1182-1186 ◽

Cited By ~ 8

Author(s):

Ivan Orlov ◽

Lukas Palatinus ◽

Gervais Chapuis

Keyword(s):

Crystal Structure ◽

Dimensional Space ◽

Flexible Structures ◽

Three Dimensional ◽

Real Space ◽

Space Group ◽

Space Groups ◽

Group A ◽

Modular Composition ◽

Three Dimensional Space

The symmetry of a commensurately modulated crystal structure can be described in two different ways: in terms of a conventional three-dimensional space group or using the superspace concept in (3 +d) dimensions. The three-dimensional space group is obtained as a real-space section of the (3 +d) superspace group. A complete network was constructed linking (3 + 1) superspace groups and the corresponding three-dimensional space groups derived from rational sections. A database has been established and is available at http://superspace.epfl.ch/finder/. It is particularly useful for finding common superspace groups for various series of modular (`composition-flexible') structures and phase transitions. The use of the database is illustrated with examples from various fields of crystal chemistry.

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Does the crystal structure of vanadium nitrogenase contain a reaction intermediate? Evidence from quantum refinement

JBIC Journal of Biological Inorganic Chemistry ◽

10.1007/s00775-020-01813-z ◽

2020 ◽

Vol 25 (6) ◽

pp. 847-861

Author(s):

Lili Cao ◽

Octav Caldararu ◽

Ulf Ryde

Keyword(s):

Crystal Structure ◽

Active Site ◽

Bound State ◽

Real Space ◽

Quantum Mechanical ◽

Storage Site ◽

Quantum Mechanical Calculations ◽

Reaction Intermediate ◽

Sulphide Ions ◽

Vanadium Nitrogenase

Abstract Recently, a crystal structure of V-nitrogenase was presented, showing that one of the µ2 sulphide ions in the active site (S2B) is replaced by a lighter atom, suggested to be NH or NH2, i.e. representing a reaction intermediate. Moreover, a sulphur atom is found 7 Å from the S2B site, suggested to represent a storage site for this ion when it is displaced. We have re-evaluated this structure with quantum refinement, i.e. standard crystallographic refinement in which the empirical restraints (employed to ensure that the final structure makes chemical sense) are replaced by more accurate quantum–mechanical calculations. This allows us to test various interpretations of the structure, employing quantum–mechanical calculations to predict the ideal structure and to use crystallographic measures like the real-space Z-score and electron-density difference maps to decide which structure fits the crystallographic raw data best. We show that the structure contains an OH−-bound state, rather than an N2-derived reaction intermediate. Moreover, the structure shows dual conformations in the active site with ~ 14% undissociated S2B ligand, but the storage site seems to be fully occupied, weakening the suggestion that it represents a storage site for the dissociated ligand. Graphic abstract

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Processing of silicon carbide ceramics using chemically modified polycarbosilanes

Journal of Materials Research ◽

10.1557/jmr.1999.0028 ◽

1999 ◽

Vol 14 (1) ◽

pp. 189-195 ◽

Cited By ~ 4

Author(s):

Sachiko Okuzaki ◽

Yuji Iwamoto ◽

Shinji Kondoh ◽

Koichi Kikuta ◽

Shin-ichi Hirano

Keyword(s):

Silicon Carbide ◽

Phase Transformation ◽

Nucleation Site ◽

Metal Alkoxide ◽

Transformation Behavior ◽

Ceramic Yield ◽

Chemically Modified ◽

Α Phase ◽

Carbide Ceramics ◽

Silicon Carbide Ceramics

Chemically modified polycarbosilane (PC) which contains Si–Al–C–O component, PCOAl, was synthesized using PC and aluminum triisopropoxide. Ceramic yield was greatly improved through the modification of PC with a metal alkoxide. The phase transformation behavior and microstructure development of silicon carbide (SiC) were studied on β–SiC powders coated with chemically modified PC. The β-α phase transformation of SiC was enhanced by the coating of chemically modified PC on β–SiC powder. A unique microstructure with submicron-sized plate-like grains was developed, since the fine a phase produced at low temperature served as a nucleation site for the β-α phase transformation of SiC.

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Crystal Structure of Silicon Carbide of 174 Layers

Journal of the Physical Society of Japan ◽

10.1143/jpsj.15.99 ◽

1960 ◽

Vol 15 (1) ◽

pp. 99-105 ◽

Cited By ~ 9

Author(s):

Takanori Tomita

Keyword(s):

Crystal Structure ◽

Silicon Carbide

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Determination of the Intermetallic α-Phase Crystal Structure in Aluminum Alloys Solidified at Rapid Cooling Rates

Light Metals 2019 - The Minerals, Metals & Materials Series ◽

10.1007/978-3-030-05864-7_17 ◽

2019 ◽

pp. 121-127

Author(s):

Joseph Jankowski ◽

Michael Kaufman ◽

Amy Clarke ◽

Krish Krishnamurthy ◽

Paul Wilson

Keyword(s):

Crystal Structure ◽

Aluminum Alloys ◽

Cooling Rates ◽

Rapid Cooling ◽

Α Phase ◽

Phase Crystal

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New BEDT-TTF/[Fe(C5O5)3]3-Hybrid System: Synthesis, Crystal Structure, and Physical Properties of a Chirality-Induced α Phase and a Novel Magnetic Molecular Metal

Inorganic Chemistry ◽

10.1021/ic062152m ◽

2007 ◽

Vol 46 (11) ◽

pp. 4446-4457 ◽

Cited By ~ 27

Author(s):

Eugenio Coronado ◽

Simona Curreli ◽

Carlos Giménez-Saiz ◽

Carlos J. Gómez-García ◽

Paola Deplano ◽

...

Keyword(s):

Crystal Structure ◽

Physical Properties ◽

Hybrid System ◽

System Synthesis ◽

Α Phase

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Predicted and experimental crystal structures of ethyl-tert-butyl ether

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768111001169 ◽

2011 ◽

Vol 67 (2) ◽

pp. 155-162 ◽

Cited By ~ 8

Author(s):

Sonja M. Hammer ◽

Edith Alig ◽

Lothar Fink ◽

Martin U. Schmidt

Keyword(s):

Crystal Structure ◽

Crystal Structures ◽

Global Minimum ◽

Lattice Energy ◽

Real Space ◽

Energy Structure ◽

Butyl Ether ◽

Crystallization Experiments ◽

Rank 2 ◽

Experimental Crystal

Possible crystal structures of ethyl-tert-butyl ether (ETBE) were predicted by global lattice-energy minimizations using the force-field approach. 33 structures were found within an energy range of 2 kJ mol−1 above the global minimum. Low-temperature crystallization experiments were carried out at 80–160 K. The crystal structure was determined from X-ray powder data. ETBE crystallizes in C2/m, Z = 4, with molecules on mirror planes. The ETBE molecule adopts a trans conformation with a (CH3)3C—O—C—C torsion angle of 180°. The experimental structure corresponds with high accuracy to the predicted structure with energy rank 2, which has an energy of 0.54 kJ mol−1 above the global minimum and is the most dense low-energy structure. In some crystallization experiments a second polymorph was observed, but the quality of the powder data did not allow the determination of the crystal structure. Possibilities and limitations are discussed for solving crystal structures from powder diffraction data by real-space methods and lattice-energy minimizations.

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