Low-Symmetry Nanophotonics

Several TEM investigations have attempted to correlate the structural characteristics to the unusual shape memory effect in NiTi, the consensus being the essence of the memory effect is ostensible manifest in the structure of NiTi transforming martensitic- ally from a B2 ordered lattice to a low temperature monoclinic phase. Commensurate with the low symmetry of the martensite phase, many variants may form from the B2 lattice explaining the very complex transformed microstructure. The microstructure may also be complicated by the enhanced formation of oxide or hydride phases and precipitation of intermetallic compounds by electron beam exposure. Variants are typically found in selfaccommodation groups with members of a group internally twinned and the twins themselves are often observed to be internally twinned. Often the most salient feature of a group of variants is their close clustering around a given orientation. Analysis of such orientation relationships may be a key to determining the nature of the reaction path that gives the transformation its apparently perfect reversibility.

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The usefulness of high index low symmetry zone axes for holz line analysis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126718 ◽

1987 ◽

Vol 45 ◽

pp. 384-385

Author(s):

C. M. Sung ◽

D. B. Williams

Keyword(s):

Lattice Parameter ◽

High Order ◽

Zone Axis ◽

High Index ◽

High Symmetry ◽

Second Phases ◽

Line Patterns ◽

Low Symmetry ◽

Line Analysis

Researchers have tended to use high symmetry zone axes (e.g. <111> <114>) for High Order Laue Zone (HOLZ) line analysis since Jones et al reported the origin of HOLZ lines and described some of their applications. But it is not always easy to find HOLZ lines from a specific high symmetry zone axis during microscope operation, especially from second phases on a scale of tens of nanometers. Therefore it would be very convenient if we can use HOLZ lines from low symmetry zone axes and simulate these patterns in order to measure lattice parameter changes through HOLZ line shifts. HOLZ patterns of high index low symmetry zone axes are shown in Fig. 1, which were obtained from pure Al at -186°C using a double tilt cooling holder. Their corresponding simulated HOLZ line patterns are shown along with ten other low symmetry orientations in Fig. 2. The simulations were based upon kinematical diffraction conditions.

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Strain measurement by means of bend contour microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153026 ◽

1989 ◽

Vol 47 ◽

pp. 210-211

Author(s):

Philip D. Hren

Keyword(s):

Strain Measurement ◽

Large Angle ◽

Single Crystal Silicon ◽

Convergent Beam Electron Diffraction ◽

Zone Axis ◽

Silicon Membrane ◽

Crystal Silicon ◽

Contour Pattern ◽

Convergent Beam ◽

Low Symmetry

The pattern of bend contours which appear in the TEM image of a bent or curled sample indicates the shape into which the specimen is bent. Several authors have characterized the shape of their bent foils by this method, most recently I. Bolotov, as well as G. Möllenstedt and O. Rang in the early 1950’s. However, the samples they considered were viewed at orientations away from a zone axis, or at zone axes of low symmetry, so that dynamical interactions between the bend contours did not occur. Their calculations were thus based on purely geometric arguments. In this paper bend contours are used to measure deflections of a single-crystal silicon membrane at the (111) zone axis, where there are strong dynamical effects. Features in the bend contour pattern are identified and associated with a particular angle of bending of the membrane by reference to large-angle convergent-beam electron diffraction (LACBED) patterns.

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The scope and limitations of cyanide groups as direction labels for the conformational analysis of matrix-isolated molecules of low symmetry. Part 2: 3-Cyanophenyl azide and two conformationally restrained derivatives

Spectrochimica Acta Part A Molecular Spectroscopy ◽

10.1016/s0584-8539(97)81428-6 ◽

1997 ◽

Vol 53 (2) ◽

pp. 141-150 ◽

Cited By ~ 1

Author(s):

I Dunkin

Keyword(s):

Conformational Analysis ◽

Conformationally Restrained ◽

Low Symmetry ◽

Isolated Molecules

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LOW SYMMETRY CRYSTAL FIELD IN LITHIUM SPINEL

Le Journal de Physique Colloques ◽

10.1051/jphyscol:19711296 ◽

1971 ◽

Vol 32 (C1) ◽

pp. C1-847-C1-849

Author(s):

M. P. PIETROV ◽

H. SZYMCZAK ◽

R. WADAS ◽

W. WARDZYNSKI

Keyword(s):

Crystal Field ◽

Low Symmetry

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The distribution of minerals in hyper-agpaitic rocks in terms of symmetry: evolution of views on the number and symmetry of minerals

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/ggub.v190.5176 ◽

2001 ◽

pp. 73-82 ◽

Cited By ~ 2

Author(s):

Alexander P. Khomyakov

Keyword(s):

Crystal Structures ◽

21St Century ◽

Special Interest ◽

Periodic Table ◽

Mineral Species ◽

Original Series ◽

Temperature Range ◽

The Earth ◽

High Alkalinity ◽

Low Symmetry

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Khomyakov, A. P. (2001). The distribution of minerals in hyper-agpaitic rocks in terms of symmetry: evolution of views on the number and symmetry of minerals. Geology of Greenland Survey Bulletin, 190, 73-82. https://doi.org/10.34194/ggub.v190.5176 _______________ Among the unique mineral localities of the Earth the complexes of nepheline syenites with hyper-agpaitic differentiates are of special interest due to their extreme diversity of mineral species. The four best studied complexes of this type – Khibina, Lovozero, Ilímaussaq and Mont Saint-Hilaire – have yielded more than 700 mineral species of which about 200 are new. The great mineral diversity is due to the combination of several factors, the most important of which is the extremely high alkalinity of agpaitic magmas, causing about half of the elements of the periodic table to be concentrated together. Minerals from hyper-agpaitic rocks are characterised by the predominance of highly ordered, low-symmetry crystal structures resulting, in particular, from the markedly extended temperature range of crystallisation. Generalisation of available data for unique mineral localities underpins the hypothesis that there is no natural limit to the number of mineral species. It is predicted that by the middle of the 21st century, the overall number of minerals recorded in nature will exceed 10 000, with the proportion of triclinic species increasing from the present 9% to 14.5%, and that of cubic species decreasing from 10% to 5%.

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Raman spectra from a low-symmetry form of mercury(I) fluoride

Journal of Physics Condensed Matter ◽

10.1088/0953-8984/2/39/001 ◽

1990 ◽

Vol 2 (39) ◽

pp. 7877-7881 ◽

Cited By ~ 3

Author(s):

S Emura

Keyword(s):

Raman Spectra ◽

Low Symmetry

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Magnetic crystalline-symmetry-protected axion electrodynamics and field-tunable unpinned Dirac cones in EuIn2As2

Nature Communications ◽

10.1038/s41467-021-21154-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

S. X. M. Riberolles ◽

T. V. Trevisan ◽

B. Kuthanazhi ◽

T. W. Heitmann ◽

F. Ye ◽

...

Keyword(s):

Density Functional ◽

Surface States ◽

Antiferromagnetic Order ◽

Functional Theory ◽

Magnetic Symmetry ◽

Integer Quantum ◽

Symmetry Protected ◽

Topological Crystalline Insulator ◽

Low Symmetry ◽

Crystalline Symmetry

AbstractKnowledge of magnetic symmetry is vital for exploiting nontrivial surface states of magnetic topological materials. EuIn2As2 is an excellent example, as it is predicted to have collinear antiferromagnetic order where the magnetic moment direction determines either a topological-crystalline-insulator phase supporting axion electrodynamics or a higher-order-topological-insulator phase with chiral hinge states. Here, we use neutron diffraction, symmetry analysis, and density functional theory results to demonstrate that EuIn2As2 actually exhibits low-symmetry helical antiferromagnetic order which makes it a stoichiometric magnetic topological-crystalline axion insulator protected by the combination of a 180∘ rotation and time-reversal symmetries: $${C}_{2}\times {\mathcal{T}}={2}^{\prime}$$ C 2 × T = 2 ′ . Surfaces protected by $${2}^{\prime}$$ 2 ′ are expected to have an exotic gapless Dirac cone which is unpinned to specific crystal momenta. All other surfaces have gapped Dirac cones and exhibit half-integer quantum anomalous Hall conductivity. We predict that the direction of a modest applied magnetic field of μ0H ≈ 1 to 2 T can tune between gapless and gapped surface states.

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