An optical method of studying the diffraction from imperfect crystals I. Modulated structures

1957 ◽  
Vol 239 (1217) ◽  
pp. 184-191 ◽  
Keyword(s):  
Diffraction Pattern ◽  
Optical Method ◽  
Photographic Plate ◽  
Flat Glass ◽  
Lattice Parameter ◽  
Optical Diffraction ◽  
Age Hardening ◽  
Two Dimensional ◽  
Structure Amplitude ◽  
Modulated Structures

The correspondence between the X-ray diffraction pattern of a crystal and the optical diffraction pattern of a two-dimensional grating has been used to determine the nature of the diffraction from imperfect crystals. A two-dimensional grating representing the structure of the imperfect crystal is prepared on a very fine-grained photographic plate by a technique which gives an error of less than 1 μ in the positions of the elements of the grating. The grating is placed in a bath of cedar-wood oil between optically flat glass plates, and its Fraunhofer diffraction pattern is observed in a modified Lipson diffractometer. Illustrations are given of the application of the optical method to the study of the diffraction from modulated structures, such as the alloy Cu 4 FeNi 3 with a periodic variation of lattice parameter, and the age-hardening aluminium-copper alloy with a variation of both lattice parameter and structure amplitude.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

High-Resolution Cryo-Electron Microscopy of Biological Macromolecules

1990 ◽  
Vol 48 (1) ◽  
pp. 126-127
Author(s):  
Yoshinori Fujiyoshi
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Diffraction Pattern ◽  
Superfluid Helium ◽  
Copper Phthalocyanine ◽  
Optical Diffraction ◽  
Irradiation Damage ◽  
Biological Macromolecules ◽  
Cross Sectional ◽  
Instrumental Resolution

The resolution of direct images of biological macromolecules is normally restricted to far less than 0.3 nm. This is not due instrumental resolution, but irradiation damage. The damage to biological macromolecules may expect to be reduced when they are cooled to a very low temperature. We started to develop a new cryo-stage for a high resolution electron microscopy in 1983, and successfully constructed a superfluid helium stage for a 400 kV microscope by 1986, whereby chlorinated copper-phthalocyanine could be photographed to a resolution of 0.26 nm at a stage temperature of 1.5 K. We are continuing to develop the cryo-microscope and have developed a cryo-microscope equipped with a superfluid helium stage and new cryo-transfer device.The New cryo-microscope achieves not only improved resolution but also increased operational ease. The construction of the new super-fluid helium stage is shown in Fig. 1, where the cross sectional structure is shown parallel to an electron beam path. The capacities of LN2 tank, LHe tank and the pot are 1400 ml, 1200 ml and 3 ml, respectively. Their surfaces are placed with gold to minimize thermal radiation. Consumption rates of liquid nitrogen and liquid helium are 170 ml/hour and 140 ml/hour, respectively. The working time of this stage is more than 7 hours starting from full LN2 and LHe tanks. Instrumental resolution of our cryo-stage cooled to 4.2 K was confirmed to be 0.20 nm by an optical diffraction pattern from the image of a chlorinated copper-phthalocyanine crystal. The image and the optical diffraction pattern are shown in Fig. 2 a, b, respectively.

The Organization of Actin Filaments in the Stereocilia of the Bird Cochlea

1980 ◽  
Vol 38 ◽  
pp. 554-555
Author(s):  
E.J. Battles ◽  
D. DeRosier ◽  
J.C. Saunders ◽  
L.G. Tilney
Keyword(s):  
Hair Cell ◽  
Diffraction Pattern ◽  
Sea Urchin ◽  
Actin Filaments ◽  
Optical Diffraction ◽  
Dense Material ◽  
Apical Surface ◽  
Structural Rigidity ◽  
High Degree ◽  
Degree Of Order

Extending from the apical surface of each hair cell of the chick cochlea are from 75 to 200 microvilli or stereocllia and one true cllium, the kinocilium. The stereocllia are arranged in rows of progressively increasing length (Fig. 1). Within each tapering sterocilium is a bundle of actin filaments with over 900 filaments near the tip yet only approximately 25 at the base where filaments are enmeshed in a dense material (Fig. 1); from here some of the filaments enter the apical surface of the cell (cuticular plate) as a rootlet. Examination of longitudinal sections of the stereocilia (Fig. 2) show that the filaments are aligned parallel to each other and show considerable order. Examination of an optical diffraction pattern of this bundle (Fig. 4) reveal that the actin filaments are packed such that the crossover points of adjacent actin filaments are inregister. A prominent reflection at 125Å−1 demonstrates that the filaments are cjossbridged by a macromolecular bridge situated at an average of 125Å−1 intervals (Fig. 4) in transverse sections the filaments appear hexagonally packed although there are regions where the filaments are less ordered (Fig. 3). In images processed in the computer to remove, noise and enhance detail periodic nature of the bridge can be clearly seen (see arrows Fig. 5). This image resembles that of an actin paracrystal formed from sea urchin extract composed of bundles of actin filaments crossbridged by a second protein. Thus the actin filaments in the bird stereocilia by being cross-bridged and packed with a high degree of order and produces a structure with considerable structural rigidity. Embryos were studied at various stages in development in an attempt to determine how the stereocilia form and how does the actin packing develops. These stages will be discussed.

scholarly journals Two-dimensional semiconductors pave the way towards dopant-based quantum computing

2018 ◽  
Vol 9 ◽  
pp. 2668-2673 ◽  
Author(s):  
José Carlos Abadillo-Uriel ◽  
Belita Koiller ◽  
María José Calderón
Keyword(s):  
Conduction Band ◽  
Quantum Computer ◽  
2D Materials ◽  
Exchange Interactions ◽  
Lattice Parameter ◽  
Oscillatory Behavior ◽  
Conduction Band Edge ◽  
Two Dimensional ◽  
Tunnel Coupling ◽  
Qubit Operations

Since the proposal in 1998 to build a quantum computer using dopants in silicon as qubits, much progress has been made in the nanofabrication of semiconductors and the control of charge and spins in single dopants. However, an important problem remains unsolved, namely the control over exchange interactions and tunneling between two donors, which presents a peculiar oscillatory behavior as the dopants relative positions vary at the scale of the lattice parameter. Such behavior is due to the valley degeneracy in the conduction band of silicon, and does not occur when the conduction-band edge is at k = 0. We investigate the possibility of circumventing this problem by using two-dimensional (2D) materials as hosts. Dopants in 2D systems are more tightly bound and potentially easier to position and manipulate. Moreover, many of them present the conduction band minimum at k = 0, thus no exchange or tunnel coupling oscillations. Considering the properties of currently available 2D semiconductor materials, we access the feasibility of such a proposal in terms of quantum manipulability of isolated dopants (for single qubit operations) and dopant pairs (for two-qubit operations). Our results indicate that a wide variety of 2D materials may perform at least as well as, and possibly better, than the currently studied bulk host materials for donor qubits.

scholarly journals VISUALISASI STRUKTUR KRISTAL KERAMIK PEROVSKITE MENGGUNAKAN VESTA

2018 ◽  
Vol 15 (1) ◽  
pp. 46
Author(s):  
Sundami Restiana ◽  
Ari Sulistyo Rini
Keyword(s):  
Crystal Structure ◽  
Diffraction Pattern ◽  
Critical Concentration ◽  
Ceramic Materials ◽  
Lattice Parameter ◽  
Peak Position ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Information ◽  
Software Program

Visualization of crystal structures and simulation of X-ray diffraction patterns of perovskite ceramic was successfully performed by VESTA software programs. The purpose of this research is to obtain the relation of lattice parameter, and composition to the diffraction pattern. The software program produces crystal structure information and a representative X-ray diffraction pattern for the ceramic materials. The program needs several input parameters such as the coordinates of each constituent atom, lattice parameters, and space symmetry. The obtained output of the software program are in the form of diffraction pattern graph and crystal structure data which gives the description of the profile and type (phase) of ceramic material. The results showed that the peak position and intensity of the diffraction pattern are influenced by the arrangement of  the atoms within the unit cell. The addition of impurity atoms such as Sr on the Ba side in BaTiO3 causes the BaTiO3 structure changes from Orthorombic (a≠b≠c) to Tetragonal (a=b≠c) structure. Based on the simulation, it can be predicted that the critical concentration of the change of structure occur at Sr concentration about 0.4.

scholarly journals Crystallinity fitting using cellulose crystallite models

2014 ◽  
Vol 70 (a1) ◽  
pp. C1135-C1135
Author(s):  
Patrik Ahvenainen ◽  
Ritva Serimaa
Keyword(s):  
Diffraction Pattern ◽  
Cell Structure ◽  
Unit Cell ◽  
Scattering Data ◽  
Crystalline Cellulose ◽  
Two Dimensional ◽  
Cellulose Crystallite ◽  
Cellulose Iβ ◽  
Diffraction Peaks ◽  
Unit Cell Structure

Cellulose is the most abundant biopolymer on Earth and hence it has enormous potential as a source of renewable energy. The nanoscale properties of cellulose are also import for the wood and papermaking industries. The atomic level structure of naturally occurring cellulose Iβ allomorph is well known [1] and this atomistic model is employed in this study for the cellulose unit cell structure. The cellulose crystallinity cannot be measured directly with scattering methods, but the crystallinity of the sample can be estimated by fitting models of crystalline and amorphous contributions to the sample intensity profile. The crystallinity fitting can be enhanced by improving the cellulose fitting model or the amorphous model. We focus on the cellulose crystallite model. The nanoscale level organization of crystalline cellulose in different plant materials is less well established that the unit cell structure of cellulose Iβ. Information on the texture of the sample is obtained efficiently by measuring the sample with a two-dimensional detector. The two-dimensional diffraction pattern can be used to obtain a wealth of information in one measurement, including the crystallite size, crystallite orientation and the crystallinity of the sample. The small size of cellulose crystallites in the wood cell wall limits the information obtainable from the diffraction pattern as the diffraction peaks widen and overlap. The overlapping of certain diffraction peaks can be studied at least qualitatively by computing the diffraction patterns from crystallite models of varying dimensions. Different models for cellulose crystallite have been suggested in the literature, such as the 36 chain model [2]. We investigate how the crystallinity fitting is influenced by the selected cellulose crystallite model and evaluate the suitability of different models to experimental X-ray scattering data of plant material, wood and highly crystalline cellulose.

scholarly journals Measuring the dihedral angle of water at a grain boundary in ice by an optical diffraction method

1991 ◽  
Vol 37 (125) ◽  
pp. 107-112 ◽  
Author(s):  
M.E.R. Walford ◽  
J.F. Nye
Keyword(s):  
Grain Boundary ◽  
Diffraction Pattern ◽  
Dihedral Angle ◽  
Boundary Energy ◽  
Monochromatic Light ◽  
Diffraction Method ◽  
Optical Diffraction ◽  
Optical Measurements ◽  
Polycrystalline Ice ◽  
Ice Water

AbstractOptical measurements have been made on the water lenses which form under pressure at grain boundaries in polycrystalline ice. Monochromatic light from a point source is focused by the lenses but, because the lenses are microscopic in size, the image is blurred by diffraction. The diffraction pattern observed under a microscope has been compared with the computed diffraction pattern to deduce the angle 2θat the rim of each lens. This is the dihedral angle for water at a grain boundary in ice, and gives the ratio of the grain-boundary energy to that of an ice-water interface. The most sensitive measurements are those made on the rings of the virtual diffraction pattern formed on the object side of the lens. They giveθ= 12.5 ± 0.5° for the grain boundary under observation, which is 26% lower than the previous value forθfound by ignoring diffraction.

Two-Dimensional Diffraction Pattern by a Silk Cloth

2020 ◽  
Vol 58 (1) ◽  
pp. 46-47
Author(s):  
Ravi Kant Avvari
Keyword(s):  
Diffraction Pattern ◽  
Two Dimensional ◽  
Silk Cloth
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