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Sebastian Schenk, Stefan Förster, Klaus Meinel, Rene Hammer, Bettina Leibundgut, Maximilian Paleschke, Jonas Pantzer, Christoph Dresler, Florian Schumann, Wolf Widdra
We report on the formation of a SrTiO<sub>3</sub>-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(111). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO<sub>3</sub>-derived OQC exhibits strong similarities to the BaTiO<sub>3</sub>-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO<sub>3</sub>-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
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
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
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
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
Harini Pattabhiraman, Marjolein Dijkstra
A two-dimensional dodecagonal quasicrystal was previously reported by Dotera et al (2014 Nature 506 208) in a system of particles interacting with a hard core of diameter σ and a repulsive square shoulder of diameter [Formula: see text]. In the current work, we examine the formation of this quasicrystal using bond orientational order parameters, correlation functions and tiling distributions. We find that this dodecagonal quasicrystal forms from a fluid phase. We further study the effect of the width of the repulsive shoulder by simulating the system over a range of values of δ...
March 8, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Janusz Wolny, Ireneusz Buganski, Pawel Kuczera, Radoslaw Strzalka
A very serious concern of scientists dealing with crystal structure refinement, including theoretical research, pertains to the characteristic bias in calculated versus measured diffraction intensities, observed particularly in the weak reflection regime. This bias is here attributed to corrective factors for phonons and, even more distinctly, phasons, and credible proof supporting this assumption is given. The lack of a consistent theory of phasons in quasicrystals significantly contributes to this characteristic bias...
December 1, 2016: Journal of Applied Crystallography
Kun Zhang, Yue Xu, Tian-Yong Chen, Hao Jing, Wen-Bo Shi, Bo Xiong, Ru-Wen Peng, Mu Wang
In this Letter, we present hybrid strong coupling between multiple photonic modes and excitons in an organic-dye-attached photonic quasicrystal. The excitons effectively interact with the photonic modes offered by the photonic quasicrystal, and multiple hybrid polariton bands are demonstrated in both experiments and calculations. Furthermore, by retrieving the measured dispersion map, we get the mixing fractions of photonic modes and excitons, and show that the polariton bands inherit not only the energy dispersion features, but also the damping behaviors from both the photonic modes and the excitons...
December 15, 2016: Optics Letters
Jolly Xavier, Jürgen Probst, Christiane Becker
Exotic manipulation of the flow of photons in nanoengineered materials with an aperiodic distribution of nanostructures plays a key role in efficiency-enhanced broadband photonic and plasmonic technologies for spectrally tailorable integrated biosensing, nanostructured thin film solarcells, white light emitting diodes, novel plasmonic ensembles etc. Through a generic deterministic nanotechnological route here we show subwavelength-scale silicon (Si) nanostructures on nanoimprinted glass substrate in large area (4 cm(2)) with advanced functional features of aperiodic composite nanophotonic lattices...
December 12, 2016: Scientific Reports
Luca Bindi, Chaney Lin, Chi Ma, Paul J Steinhardt
We report the first occurrence of an icosahedral quasicrystal with composition Al62.0(8)Cu31.2(8)Fe6.8(4), outside the measured equilibrium stability field at standard pressure of the previously reported Al-Cu-Fe quasicrystal (AlxCuyFez, with x between 61 and 64, y between 24 and 26, z between 12 and 13%). The new icosahedral mineral formed naturally and was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite that experienced shock metamorphism, local melting (with conditions exceeding 5 GPa and 1,200 °C in some locations), and rapid cooling, all of which likely resulted from impact-induced shock in space...
December 8, 2016: Scientific Reports
Kan Yue, Mingjun Huang, Ryan L Marson, Jinlin He, Jiahao Huang, Zhe Zhou, Jing Wang, Chang Liu, Xuesheng Yan, Kan Wu, Zaihong Guo, Hao Liu, Wei Zhang, Peihong Ni, Chrys Wesdemiotis, Wen-Bin Zhang, Sharon C Glotzer, Stephen Z D Cheng
Frank-Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails...
December 13, 2016: Proceedings of the National Academy of Sciences of the United States of America
Bruno Alessandro Silva Guedes de Lima, Rodinei Medeiros Gomes, Severino Jackson Guedes de Lima, Diana Dragoe, Marie-Geneviève Barthes-Labrousse, Richard Kouitat-Njiwa, Jean-Marie Dubois
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a γ-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (µ ≤ 6% against sintered tungsten carbide), in contrast to the state of the art...
2016: Science and Technology of Advanced Materials
Edyta Słyk, Wojciech Rżysko, Paweł Bryk
Using Monte Carlo simulation we study two dimensional mixtures of patchy and spherically symmetric particles. Such mixtures can be synthesized experimentally by covering colloids with appropriate types of DNA strands [L. Feng, et al., Adv. Mater., 2013, 25, 2779]. We focus on finding out the ordered structures that can be formed in such systems. The type of ordered phase strongly depends on the valency, size and binding energy of the patchy particles. If the patch size is small enough, i.e. it allows only one spherically symmetric particle to be bound, the ordered structure follows either a hexagonal or a tetragonal pattern depending on the valency of the patchy particles...
November 11, 2016: Soft Matter
Aleks Reinhardt, John S Schreck, Flavio Romano, Jonathan P K Doye
We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta- and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm 'star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms...
November 10, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Zhong Wang, Wenxing Liu, Tianbao Yu, Tongbiao Wang, Haoming Li, Nianhua Liu, Qinghua Liao
We report the properties of dual phononic-photonic band gaps and localized modes of eightfold lithium niobate (LiNbO<sub>3</sub>) phoxonic quasicrystals (PhXQCs). Complete and large phoxonic band gaps are easily achieved despite the low refractive index of LiNbO<sub>3</sub> substrate. Point defect intentionally introduced can form localized modes within both forbidden and transparency bands over a wide range of geometric parameters. Further analysis indicates that the localized modes within transparency bands originate from the intrinsic high-order rotational symmetry of quasiperiodic structures, which resemble whispering gallery modes...
October 3, 2016: Optics Express
Alfredo Metere, Peter Oleynikov, Mikhail Dzugutov, Sven Lidin
We report a solid smectic phase that exhibits dodecagonal global order. It is composed of axially stacked hexagonally ordered particle layers, and its 12-fold rotational symmetry induced by the 30° rotation of adjacent layers with respect to each other. A quasicrystal was produced in a molecular-dynamics simulation of a single-component system of particles interacting via a spherically-symmetric potential. It was formed as a result of a first-order phase transition from an isotropic liquid state that occurred under constant-density cooling...
September 16, 2016: Soft Matter
V Brajuskovic, F Barrows, C Phatak, A K Petford-Long
Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations...
October 3, 2016: Scientific Reports
Joyce Pham, Andreas Kreyssig, Alan I Goldman, Gordon J Miller
A new icosahedral quasicrystalline phase, CaAu4.5-xAl1.5+x [0.11 ≤ x ≤ 0.40(6); CaAu4.4Al1.6, aQC = 5.383(4) Å, and Pm3̅ 5̅], and its lowest-order 1/0 cubic crystalline approximant phase, CaAu3+xAl1-x [0 ≤ x ≤ 0.31(1); a = 9.0766(5)-9.1261(8) Å, Pa3̅ (No. 205), and Pearson symbol cP40], have been discovered in the Ca-poor region of the Ca-Au-Al system. In the crystalline approximant, eight [Au3-xAl1+x] tetrahedra fill the unit cell, and each tetrahedron is surrounded by four Ca atoms, thus forming a three-dimensional network of {Ca4/4[Au3-xAl1+x]} tetrahedral stars...
October 17, 2016: Inorganic Chemistry
Xingchen Ye, Jun Chen, M Eric Irrgang, Michael Engel, Angang Dong, Sharon C Glotzer, Christopher B Murray
Expanding the library of self-assembled superstructures provides insight into the behaviour of atomic crystals and supports the development of materials with mesoscale order. Here we build on recent findings of soft matter quasicrystals and report a quasicrystalline binary nanocrystal superlattice that exhibits correlations in the form of partial matching rules reducing tiling disorder. We determine a three-dimensional structure model through electron tomography and direct imaging of surface topography. The 12-fold rotational symmetry of the quasicrystal is broken in sublayers, forming a random tiling of rectangles, large triangles and small triangles with 6-fold symmetry...
September 26, 2016: Nature Materials
S Förster, M Trautmann, S Roy, W A Adeagbo, E M Zollner, R Hammer, F O Schumann, K Meinel, S K Nayak, K Mohseni, W Hergert, H L Meyerheim, W Widdra
We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3^{2}.4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO_{3} clusters, leading to a fundamental edge length of the tiling 6...
August 26, 2016: Physical Review Letters
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