scholarly journals X-ray diffraction investigation of a three-dimensional Si/SiGe quantum dot crystal

2009 ◽  
Vol 79 (3) ◽  
Author(s):  
Vaclav Holý ◽  
Julian Stangl ◽  
Thomas Fromherz ◽  
Rainer T. Lechner ◽  
Eugene Wintersberger ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sige Quantum Dot

scholarly journals Coplanar and grazing incidence x-ray-diffraction investigation of self-organized SiGe quantum dot multilayers

1998 ◽  
Vol 58 (12) ◽  
pp. 7934-7943 ◽  
Author(s):  
V. Holý ◽  
A. A. Darhuber ◽  
J. Stangl ◽  
S. Zerlauth ◽  
F. Schäffler ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Grazing Incidence ◽  
X Ray Diffraction ◽  
X Ray ◽  
Self Organized ◽  
Sige Quantum Dot

Ordering parameters of self-organized three-dimensional quantum-dot lattices determined from anomalous x-ray diffraction

2004 ◽  
Vol 84 (6) ◽  
pp. 885-887 ◽  
Author(s):  
R. T. Lechner ◽  
T. U. Schülli ◽  
V. Holý ◽  
G. Springholz ◽  
J. Stangl ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Self Organized

3D SiGe QUANTUM DOT CRYSTALS: STRUCTURAL CHARACTERIZATION AND ELECTRONIC COUPLING

2009 ◽  
Vol 23 (12n13) ◽  
pp. 2836-2841 ◽  
Author(s):  
T. FROMHERZ ◽  
J. STANGL ◽  
R. T. LECHNER ◽  
E. WINTERSBERGER ◽  
G. BAUER ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Electronic Coupling ◽  
X Ray Diffraction ◽  
Si Substrate ◽  
Subsequent Growth ◽  
X Ray ◽  
Force Microscopy ◽  
Atomic Force ◽  
Deep Uv ◽  
Sige Quantum Dot

We report on the growth of SiGe quantum dot crystals which are realized by depositing Ge on a two-dimensionally pit-patterned Si substrate and subsequent growth of Si spacer and Ge island layers. Lateral periods of 100 nm are obtained by employing deep UV lithography using synchrotron radiation. The vertical period of the typically 10 period dot superlattices was of the order of 10 nm. Ordering of the islands was investigated by atomic force microscopy as well as by high resolution x-ray diffraction studies. From the quantitative evaluation of the x-ray diffraction data a mean Ge content of about 60% in the quantum dots was obtained and an rms. deviation from ideal lattice sites of about 3 nm was found. A simulation of the eigenenergies based on the nextnano3 simulation package was used to interpret the measured photoluminescence data.

Lattice distortion in dry-etched Si/SiGe quantum dot array studied by 2D reciprocal space mapping using synchrotron X-ray diffraction

1997 ◽  
Vol 294 (1-2) ◽  
pp. 300-303 ◽  
Author(s):  
W.-X Ni ◽  
J Birch ◽  
Y.S Tang ◽  
K.B Joelsson ◽  
C Sotomayor-Torres ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Lattice Distortion ◽  
Space Mapping ◽  
Reciprocal Space ◽  
X Ray Diffraction ◽  
Reciprocal Space Mapping ◽  
X Ray ◽  
Sige Quantum Dot

Ribosome Structural Organization

1974 ◽  
Vol 32 ◽  
pp. 332-333
Author(s):  
James A. Lake
Keyword(s):  
Ribosomal Proteins ◽  
Structural Organization ◽  
Three Dimensional ◽  
Small Subunit ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Specific Antibodies ◽  
X Ray ◽  
E Coli ◽  
Complete Sequences

The understanding of ribosome structure has advanced considerably in the last several years. Biochemists have characterized the constituent proteins and rRNA's of ribosomes. Complete sequences have been determined for some ribosomal proteins and specific antibodies have been prepared against all E. coli small subunit proteins. In addition, a number of naturally occuring systems of three dimensional ribosome crystals which are suitable for structural studies have been observed in eukaryotes. Although the crystals are, in general, too small for X-ray diffraction, their size is ideal for electron microscopy.

scholarly journals An investigation of polyhedral deformation in two mixed-metal diarsenates: SrZnAs2O7and BaCuAs2O7

2015 ◽  
Vol 71 (4) ◽  
pp. 330-337 ◽  
Author(s):  
Sabina Kovač ◽  
Ljiljana Karanović ◽  
Tamara Đorđević
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
General Formula ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Open Framework ◽  
Geometrical Characteristics ◽  
Barium Copper

Two isostructural diarsenates, SrZnAs2O7(strontium zinc diarsenate), (I), and BaCuAs2O7[barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The three-dimensional open-framework crystal structure consists of corner-sharingM2O5(M2 = Zn or Cu) square pyramids and diarsenate (As2O7) groups. Each As2O7group shares its five corners with five differentM2O5square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine-coordinatedM1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of theM1O9,M2O5and As2O7groups of known isostructural diarsenates, adopting the general formulaM1IIM2IIAs2O7(M1II= Sr, Ba, Pb;M2II= Mg, Co, Cu, Zn) and crystallizing in the space groupP21/n, are presented and discussed.

A new model for packing of type-I collagen molecules in the native fibril

1981 ◽  
Vol 1 (10) ◽  
pp. 801-810 ◽  
Author(s):  
Karl A. Piez ◽  
Benes L. Trus
Keyword(s):  
Type I Collagen ◽  
Hexagonal Lattice ◽  
Three Dimensional ◽  
Equatorial Region ◽  
Type I ◽  
X Ray Diffraction ◽  
X Ray ◽  
Left Handed ◽  
Crystal Model ◽  
Collagen Molecules

A specific fibril model is presented consisting of bundles of five-stranded microfibrils, which are usually disordered (except axially) but under lateral compression become ordered. The features are as follows (where D = 234 residues or 67 nm): (1) D-staggered collagen molecules 4.5 D long in the helical microfibril have a left-handed supercoil with a pitch of 400–700 residues, but microfibrils need not have helical symmetry. (2) Straight-tilted 0.5-D overlap regions on a near-hexagonal lattice contribute the discrete x-ray diffraction reflections arising from lateral order, while the gap regions remain disordered. (3) The overlap regions are equivalent, but are crystallographically distinguished by systematic displacements from the near-hexagonal lattice. (4) The unit cell is the same as in a recently proposed three-dimensional crystal model, and calculated intensities in the equatorial region of the x-ray diffraction pattern agree with observed values.

scholarly journals Acemetacin cocrystals and salts: structure solution from powder X-ray data and form selection of the piperazine salt

IUCrJ ◽  
2014 ◽  
Vol 1 (2) ◽  
pp. 136-150 ◽  
Author(s):  
Palash Sanphui ◽  
Geetha Bolla ◽  
Ashwini Nangia ◽  
Vladimir Chernyshev
Keyword(s):  
Hydrogen Bonds ◽  
Dissolution Rate ◽  
Aqueous Medium ◽  
Acid Amide ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Reference Drug ◽  
X Ray ◽  
Time Period ◽  
Solid Form

Acemetacin (ACM) is a non-steroidal anti-inflammatory drug (NSAID), which causes reduced gastric damage compared with indomethacin. However, acemetacin has a tendency to form a less soluble hydrate in the aqueous medium. We noted difficulties in the preparation of cocrystals and salts of acemetacin by mechanochemical methods, because this drug tends to form a hydrate during any kind of solution-based processing. With the objective to discover a solid form of acemetacin that is stable in the aqueous medium, binary adducts were prepared by the melt method to avoid hydration. The coformers/salt formers reported are pyridine carboxamides [nicotinamide (NAM), isonicotinamide (INA), and picolinamide (PAM)], caprolactam (CPR),p-aminobenzoic acid (PABA), and piperazine (PPZ). The structures of an ACM–INA cocrystal and a binary adduct ACM–PABA were solved using single-crystal X-ray diffraction. Other ACM cocrystals, ACM–PAM and ACM–CPR, and the piperazine salt ACM–PPZ were solved from high-resolution powder X-ray diffraction data. The ACM–INA cocrystal is sustained by the acid...pyridine heterosynthon and N—H...O catemer hydrogen bonds involving the amide group. The acid...amide heterosynthon is present in the ACM–PAM cocrystal, while ACM–CPR contains carboxamide dimers of caprolactam along with acid–carbonyl (ACM) hydrogen bonds. The cocrystals ACM–INA, ACM–PAM and ACM–CPR are three-dimensional isostructural. The carboxyl...carboxyl synthon in ACM–PABA posed difficulty in assigning the position of the H atom, which may indicate proton disorder. In terms of stability, the salts were found to be relatively stable in pH 7 buffer medium over 24 h, but the cocrystals dissociated to give ACM hydrate during the same time period. The ACM–PPZ salt and ACM–nicotinamide cocrystal dissolve five times faster than the stable hydrate form, whereas the ACM–PABA adduct has 2.5 times faster dissolution rate. The pharmaceutically acceptable piperazine salt of acemetacin exhibits superior stability, faster dissolution rate and is able to overcome the hydration tendency of the reference drug.

2D X-ray diffraction and molecular modelling of the crystalline structure of polyesters under uniaxial stress

2021 ◽  
pp. 096739112199822
Author(s):  
Ahmed I Abou-Kandil ◽  
Gerhard Goldbeck
Keyword(s):  
Crystalline Structure ◽  
Molecular Modelling ◽  
Three Dimensional ◽  
Uniaxial Stress ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Modelling Techniques ◽  
Diffraction Patterns

Studying the crystalline structure of uniaxially and biaxially drawn polyesters is of great importance due to their wide range of applications. In this study, we shed some light on the behaviour of PET and PEN under uniaxial stress using experimental and molecular modelling techniques. Comparing experiment with modelling provides insights into polymer crystallisation with extended chains. Experimental x-ray diffraction patterns are reproduced by means of models of chains sliding along the c-axis leading to some loss of three-dimensional order, i.e. moving away from the condition of perfect register of the fully extended chains in triclinic crystals of both PET and PEN. This will help us understand the mechanism of polymer crystallisation under uniaxial stress and the appearance of mesophases in some cases as discussed herein.

A New POM-Based Supramolecular Compound: Synthesis, Structure and Adsorptive Property of [Cu(phen)2]3[W6O19]

2014 ◽  
Vol 919-921 ◽  
pp. 2013-2016 ◽  
Author(s):  
Ya Bing Liu ◽  
Hong Jie Wang ◽  
Hong Kai Zhao
Keyword(s):  
Three Dimensional ◽  
Building Blocks ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Hybrid Compound ◽  
Adsorptive Property ◽  
X Ray ◽  
Hydrogen Bonding Interactions ◽  
Compound Synthesis ◽  
Metal Organic

A POM - based organice - inorganic hybrid compound with the chemical formula of[Cu (phen)2]3[W6O19] (phen = 1,10-phenanthroline) (1) has been hydrothermally synthesized andstructurally characterized by the elemental analysis, and single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space groupC2/c witha=18.319(4) Å,b= 17.311(4) Å,c= 22.248(4) Å,β= 112.40(3) o,V= 6523(2) Å3,Z= 4, R1= 0.0448, andwR2=0.1218. Compound 1 consists of the [W6O19]3-building blocks and [Cu (phen)2]+metal organic cationic moieties, which are packed together via the extensive hydrogen-bonding interactions to form a three-dimensional supramolecular framework. The adsorption of methylene blue (MB) under UV irradiation with 1 as the heterogeneous adsorbent has been investigated, showing a good adsorptive property of 1 for MB degradation.

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