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https://www.readbyqxmd.com/read/28639623/imaging-quasiperiodic-electronic-states-in-a-synthetic-penrose-tiling
#1
Laura C Collins, Thomas G Witte, Rochelle Silverman, David B Green, Kenjiro K Gomes
Quasicrystals possess long-range order but lack the translational symmetry of crystalline solids. In solid state physics, periodicity is one of the fundamental properties that prescribes the electronic band structure in crystals. In the absence of periodicity and the presence of quasicrystalline order, the ways that electronic states change remain a mystery. Scanning tunnelling microscopy and atomic manipulation can be used to assemble a two-dimensional quasicrystalline structure mapped upon the Penrose tiling...
June 22, 2017: Nature Communications
https://www.readbyqxmd.com/read/28636340/three-dimensional-modeling-of-quasicrystal-structures-from-x-ray-diffraction-an-icosahedral-al-cu-fe-alloy
#2
Seung-Tae Hong
Quasicrystals (QCs) are well-ordered but aperiodic crystals with classically forbidden symmetries (such as 5-fold). High-dimensional (HD) crystallography is a standard method to locate atom positions explicitly. However, in practice, it is still challenging because of its complexity. Here, we report a new simple approach to three-dimensional (3D) atomic modeling derived from X-ray diffraction data, and apply it to the icosahedral QC Al0.63Cu0.25Fe0.12. Electron density maps were calculated directly from 3D diffraction data indexed with noninteger (fractional) numbers as measured, with proper phases; each of 2(5) = 32 possible phase assignments for the five strongest reflections was used for Fourier synthesis...
June 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28595403/colloidal-diffusion-over-a-quasicrystalline-patterned-surface
#3
Yun Su, Pik-Yin Lai, Bruce J Ackerson, Xin Cao, Yilong Han, Penger Tong
We report a systematic study of colloidal diffusion over a substrate with quasicrystalline-patterned holes. Silica spheres of diameter comparable to the hole diameter diffuse over the patterned substrate and experience a gravitational potential U(x, y). Using optical microscopy, we track the particle trajectories and find two distinct states: a trapped state when the particles are inside the holes and a free-diffusion state when they are on the flat surface outside the holes. The potential U(x, y) and dynamic properties of the diffusing particle, such as its mean dwell time, mean square displacement, and long-time diffusion coefficient DL, are measured simultaneously...
June 7, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28588202/terahertz-electromagnetic-fences-on-a-graphene-surface-plasmon-polariton-platform
#4
Xidong Wu, Xiang Guo
Controlling the loss of graphene can be used in the field of transformation optics. We propose a new concept of electromagnetic fence on a monolayer graphene surface plasmon polariton platform. Using a Dot-Density-Renderer quasicrystal metasurface, we can simulate the absorption of gradient index optics structures. Numerical simulations show that the incident waves to our designed electromagnetic fence are trapped toward the central lines and quickly absorbed by the high-loss region. Two basic types of electromagnetic fence and its composite structures have been designed and analyzed, which exhibit excellent broadband absorbing performances at 8 THz-12 THz...
June 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28581782/conformational-asymmetry-and-quasicrystal-approximants-in-linear-diblock-copolymers
#5
Morgan W Schulze, Ronald M Lewis, James H Lettow, Robert J Hickey, Timothy M Gillard, Marc A Hillmyer, Frank S Bates
Small angle x-ray scattering experiments on three model low molar mass diblock copolymer systems containing minority polylactide and majority hydrocarbon blocks demonstrate that conformational asymmetry stabilizes the Frank-Kasper σ phase. Differences in block flexibility compete with space filling at constant density inducing the formation of polyhedral shaped particles that assemble into this low symmetry ordered state with local tetrahedral coordination. These results confirm predictions from self-consistent field theory that establish the origins of symmetry breaking in the ordering of block polymer melts subjected to compositional and conformational asymmetry...
May 19, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28540862/electronic-and-optical-properties-of-strained-graphene-and-other-strained-2d-materials-a-review
#6
Gerardo G Naumis, Salvador Barraza-Lopez, Maurice Oliva-Leyva, Humberto Terrones
This review presents the state of the art of strain and ripple-induced effects on the electronic and optical properties of graphene. It starts by providing the crystallographic description of mechanical deformations, as well as the diffraction pattern for different kinds of representative deformations fields. Then, the focus turns to the unique elastic properties of graphene, and to how strain is produced. Thereafter, various theoretical approaches used to study the electronic properties of strained graphene are examined, discussing the advantages of each...
May 25, 2017: Reports on Progress in Physics
https://www.readbyqxmd.com/read/28530242/interface-driven-formation-of-a-two-dimensional-dodecagonal-fullerene-quasicrystal
#7
M Paßens, V Caciuc, N Atodiresei, M Feuerbacher, M Moors, R E Dunin-Borkowski, S Blügel, R Waser, S Karthäuser
Since their discovery, quasicrystals have attracted continuous research interest due to their unique structural and physical properties. Recently, it was demonstrated that dodecagonal quasicrystals could be used as bandgap materials in next-generation photonic devices. However, a full understanding of the formation mechanism of quasicrystals is necessary to control their physical properties. Here we report the formation of a two-dimensional dodecagonal fullerene quasicrystal on a Pt3Ti(111) surface, which can be described in terms of a square-triangle tiling...
May 22, 2017: Nature Communications
https://www.readbyqxmd.com/read/28487537/evidence-of-cross-cutting-and-redox-reaction-in-khatyrka-meteorite-reveals-metallic-al-minerals-formed-in-outer-space
#8
Chaney Lin, Lincoln S Hollister, Glenn J MacPherson, Luca Bindi, Chi Ma, Christopher L Andronicos, Paul J Steinhardt
We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al2O3, occurring where silicate melt was in contact with Al-Cu-Fe alloys...
May 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28442721/near-field-surface-plasmons-on-quasicrystal-metasurfaces
#9
Quanlong Yang, Xueqian Zhang, Shaoxian Li, Quan Xu, Ranjan Singh, Yongmin Liu, Yanfeng Li, Sergey S Kruk, Jianqiang Gu, Jiaguang Han, Weili Zhang
Excitation and manipulation of surface plasmons (SPs) are essential in developing cutting-edge plasmonic devices for medical diagnostics, biochemical spectroscopy and communications. The most common approach involves designing an array of periodic slits or grating apertures that enables coupling of the incident light to the SP modes. In recent years, plasmonic resonances, including extraordinary optical transmission through periodic arrays, quasicrystals and random aperture arrays, have been investigated in the free space...
December 23, 2016: Scientific Reports
https://www.readbyqxmd.com/read/28417127/on-the-formation-of-stripe-sigma-and-honeycomb-phases-in-a-core-corona-system
#10
Harini Pattabhiraman, Marjolein Dijkstra
Using Monte Carlo simulations and free-energy calculations, we investigate the phase behaviour of a two-dimensional core-corona system. We model this system as particles consisting of an impenetrable hard core of diameter σHD surrounded by a purely repulsive soft corona of diameter δ = 1.95σHD. At low densities, we observe the spontaneous formation of a phase with a stripe texture as well as a honeycomb-like phase driven by both energy and entropy considerations. At high densities, we find that a two-dimensional analogue of the periodic sigma phase, considered as an approximant of dodecagonal quasicrystals, is energetically stabilised with respect to two distinct dodecagonal quasicrystals, namely, a square-triangle tiling and a square-triangle-shield tiling...
April 18, 2017: Soft Matter
https://www.readbyqxmd.com/read/28401877/non-close-packed-three-dimensional-quasicrystals
#11
Pablo Damasceno, Sharon Glotzer, Michael Engel
Quasicrystals are frequently encountered in condensed matter. They are important candidates for equilibrium phases from the atomic scale to the nanoscale. Here, we investigate the computational self-assembly of four quasicrystals in a single model system of identical particles interacting with a tunable isotropic pair potential. We reproduce a known icosahedral quasicrystal and report a decagonal quasicrystal, a dodecagonal quasicrystal, and an octagonal quasicrystal. The quasicrystals have low coordination number or occur in systems with mesoscale density variations...
April 12, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28358719/properties-of-quasiperiodic-functions
#12
Johannes Roth
Today, quasiperiodic tilings are well known and have been studied in great detail since they are very useful to describe the properties of metallic and soft matter quasicrystals. A closely related topic are quasiperiodic functions which have also gained large interest recently. Different types of such functions and there interrelation will be presented here. The main topic will be quasiperiodic potentials generated by laser beams and their variability. The distribution of extremal points and local isomorphisms of quasiperiodic functions will also be addressed...
March 30, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28345537/hyperuniformity-variation-with-quasicrystal-local-isomorphism-class
#13
C Lin, P J Steinhardt, S Torquato
Hyperuniformity is the suppression of long-wavelength density fluctuations, relative to typical structurally disordered systems. In this paper, we examine how the degree of hyperuniformity [[Formula: see text]] in quasicrystals depends on the local isomorphism class. By studying the continuum of pentagonal quasicrystal tilings obtained by direct projection from a five-dimensional hypercubic lattice, we find that [Formula: see text] is dominantly determined by the local distribution of vertex environments (e...
May 24, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28330366/phase-behaviour-of-quasicrystal-forming-systems-of-core-corona-particles
#14
Harini Pattabhiraman, Marjolein Dijkstra
Using Monte Carlo simulations and free-energy calculations, we study the phase behaviour of a two-dimensional system of particles interacting with a hard core of diameter σHD and a repulsive square shoulder potential. The interest in this system lies in the formation of quasicrystals of different symmetries at specific square-shoulder widths δ as previously reported by Dotera et al. [Nature 506, 208 (2014)]. However, an insight into other possible periodic phases formed in these systems and the thermodynamic stability of both the periodic and quasicrystal phases is yet to be addressed...
March 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28248662/b7-as-a-supergroup-of-crystal-and-quasicrystal-symmetries
#15
Kazimierz Stróż
In sharp contrast to the generation of a finite group that includes all the 14 types of Bravais lattices as its subgroups [Hosoya (2000). Acta Cryst. A56, 259-263; Hosoya (2002). Acta Cryst. A58, 208], it was proved that a signed permutation group Bk may be interpreted as the supergroup of both crystal and quasicrystal symmetries. Minimal dimension k = 6 is adequate for lattices referred to their three non-coplanar shortest vectors, or for symmetry groups of most quasicrystal types. If one prefers complete, well defined semi-reduced lattice descriptions or needs a dodecagonal group, the B7 supergroup is necessary...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28140368/observation-of-a-dodecagonal-oxide-quasicrystal-and-its-complex-approximant-in-the-srtio3-pt-1%C3%A2-1%C3%A2-1-system
#16
Sebastian Schenk, Stefan Förster, Klaus Meinel, René Hammer, Bettina Leibundgut, Maximilian Paleschke, Jonas Pantzer, Christoph Dresler, Florian O Schumann, Wolf Widdra
We report on the formation of a SrTiO3-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(1 1 1). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO3-derived OQC exhibits strong similarities to the BaTiO3-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO3-derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified...
January 31, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28106533/defect-structures-in-frank-kasper-type-square-triangle-tiling-of-multimodal-cage-type-mesoporous-silicas
#17
Yasuhiro Sakamoto
Multimodal cage-type mesoporous silicas (MCMSs) with Frank-Kasper type square-triangle tiling show a unique defect structure, so-called three-fold symmetric hexagons, or shields, which are caused by phason fluctuations in dodecagonal quasicrystals. We observed and characterized three types of configurations inside shields in both quasiperiodic and periodic 3(2).4.3.4 tiling of MCMSs by transmission electron microscopy (TEM). The high-resolution TEM images of the shields were well explained by polyhedral models, which are the constituents of the Frank-Kasper type tetrahedrally close-packed structures of MCMSs...
March 29, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28072393/stability-of-icosahedral-quasicrystals-in-a-simple-model-with-two-length-scales
#18
Kai Jiang, Pingwen Zhang, An-Chang Shi
The phase behaviour of a free energy functional with two length scales is examined by comparing the free energy of different candidate phases including three-dimensional icosahedral quasicrystals. Accurate free energy of the quasicrystals has been obtained using the recently developed projection method. The results reveal that the icosahedral quasicrystal and body-centred-cubic spherical phase are the stable ordered phases of the model. Furthermore, the difference between the results obtained from the projection method and the one-mode approximation has been analyzed in detail...
March 29, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28008870/detection-of-phonon-and-phason-modes-in-intrinsic-colloidal-quasicrystals-by-reconstructing-their-structure-in-hyperspace
#19
J Hielscher, M Martinsons, M Schmiedeberg, S C Kapfer
Phasons are additional degrees of freedom which occur in quasicrystals alongside the phonons known from conventional periodic crystals. The rearrangements of particles that are associated with a phason mode are hard to interpret in physical space. We reconstruct the quasicrystal structure by an embedding into extended higher-dimensional space, where phasons correspond to displacements perpendicular to the physical space. In dislocation-free decagonal colloidal quasicrystals annealed with Brownian dynamics simulations, we identify thermal phonon and phason modes...
March 8, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28003663/near-field-surface-plasmons-on-quasicrystal-metasurfaces
#20
Quanlong Yang, Xueqian Zhang, Shaoxian Li, Quan Xu, Ranjan Singh, Yongmin Liu, Yanfeng Li, Sergey S Kruk, Jianqiang Gu, Jiaguang Han, Weili Zhang
Excitation and manipulation of surface plasmons (SPs) are essential in developing cutting-edge plasmonic devices for medical diagnostics, biochemical spectroscopy and communications. The most common approach involves designing an array of periodic slits or grating apertures that enables coupling of the incident light to the SP modes. In recent years, plasmonic resonances, including extraordinary optical transmission through periodic arrays, quasicrystals and random aperture arrays, have been investigated in the free space...
December 2016: Scientific Reports
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