Twist Angle (twist + angle)

Distribution by Scientific Domains


Selected Abstracts


Oxide layer dissolution in Si/SiOx/Si wafer bonded structures

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009
N. Zakharov
Abstract The evolution of the interfaces of hydrophilic-bonded Si wafers and the corresponding low-angle twist boundary have been analysed in relation to thermal annealing and their relative crystallographic orientation. Two orientation relationships were investigated: Si<001>/Si<001> and Si<001>/Si<110>, where the interfaces are seperated by thin native SiO2 layers. The interfaces were analysed by TEM and STEM/EELS. It is found that the decomposition rate of the intermediate oxide layer and the formation of a Si(Si bonded interface depend very much on the lattice mismatch and on the twist angle. The velocity of the dissolution of the thin oxide layers and the formation of Si(Si bonds at the bonding interface depend on the orientation relations of the corresponding wafers. The processes of interface fusion and the dissolution of oxide layer are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Using 1,3-butadiene and 1,3,5-hexatriene to model the cis-trans isomerization of retinal, the chromophore in the visual pigment rhodopsin

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002
Fredrik Blomgren
Abstract The short polyenes 1,3-butadiene and 1,3,5-hexatriene are used to model the cis-trans isomerization of the protonated Schiff base of retinal (PSBR) in rhodopsin (Rh). We employed the complete active space self-consistent field (CASSCF) method for calculation of the potential energy surfaces (PESs) in C2 symmetry. In the calculations, the central bond was twisted from 0 to 180° in the first singly excited singlet state (Sse), i.e., the state dominated by a configuration with one electron excited from HOMO to LUMO. It was found that the PES of 1,3-butadiene has a maximum whereas the PES of 1,3,5-hexatriene has a minimum for a twist angle of 90°. This is explained by a shift in border of single and double bonds in the Sse state. The first step in the cis-trans isomerization of PSBR, which is the formation of the C6C7 (see Scheme 1 for numbering) twisted PSBR in the first excited singlet state (S1), inside the protein binding pocket of the visual pigment Rh is modeled using crystal coordinates and the calculations performed on 1,3-butadiene and 1,3,5-hexatriene. More specifically, a plausible approximate structure is calculated in a geometric way for the C6C7 90° twisted PSBR, which fits into the protein binding pocket in the best possible way. It has been shown earlier that PSBR has an energy minimum for this angle in S1. The CASSCF method was used to investigate the wave function of the calculated structure of PSBR. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source]


Improved lateral force calibration based on the angle conversion factor in atomic force microscopy

JOURNAL OF MICROSCOPY, Issue 2 2007
DUKHYUN CHOI
Summary A novel calibration method is proposed for determining lateral forces in atomic force microscopy (AFM), by introducing an angle conversion factor, which is defined as the ratio of the twist angle of a cantilever to the corresponding lateral signal. This factor greatly simplifies the calibration procedures. Once the angle conversion factor is determined in AFM, the lateral force calibration factors of any rectangular cantilever can be obtained by simple computation without further experiments. To determine the angle conversion factor, this study focuses on the determination of the twist angle of a cantilever during lateral force calibration in AFM. Since the twist angle of a cantilever cannot be directly measured in AFM, the angles are obtained by means of the moment balance equations between a rectangular AFM cantilever and a simple commercially available step grating. To eliminate the effect of the adhesive force, the gradients of the lateral signals and the twist angles as a function of normal force are used in calculating the angle conversion factor. To verify reliability and reproducibility of the method, two step gratings with different heights and two different rectangular cantilevers were used in lateral force calibration in AFM. The results showed good agreement, to within 10%. This method was validated by comparing the coefficient of friction of mica so determined with values in the literature. [source]


In vivo quantitative three-dimensional motion mapping of the murine myocardium with PC-MRI at 17.6 T

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2006
Volker Herold
Abstract This work presents a method that allows for the assessment of 3D murine myocardial motion in vivo at microscopic resolution. Phase-contrast (PC) magnetic resonance imaging (MRI) at 17.6 T was applied to map myocardial motion in healthy mice along three gradient directions. High-resolution velocity maps were acquired at three different levels in the murine myocardium with an in-plane resolution of 98 ,m, a slice thickness of 0.6 mm, and a temporal resolution of 6 ms. The applied PC-MRI method was validated with phantom experiments that confirmed the correctness of the method with deviations of <1.7%. Myocardial in-plane velocities between 0.5 cm/s and 2.2 cm/s were determined for the healthy murine myocardium. Through-plane velocities of 0.1,0.83 cm/s were measured. Velocity data was also used to calculate the myocardial twist angle during systole at different slices in the short-axis view. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]


Structural derivation and crystal chemistry of apatites

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003
T. J. White
The crystal structures of the [A(1)2][A(2)3](BO4)3X apatites and the related compounds [A(1)2][A(2)3](BO5)3X and [A(1)2][A(2)3](BO3)3X are collated and reviewed. The structural aristotype for this family is Mn5Si3 (D88 type, P63/mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P63/m, Cmcm and P63cm. Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1),A(1),O(2) twist angle , projected on (001) of the A(1)O6 metaprism. For apatites that contain the same A cation, it is shown that , decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P63/m symmetry or cation ordering. The inclusion of A(1)O6 metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr5(BO3)3Br. The most common symmetry for the 74 chemically distinct [A(1)2][A(2)3](BO4)3X apatites that were surveyed was P63/m (57%), with progressively more complex chemistries adopting P63 (21%), P (9%), P (4.3%), P21/m (4.3%) and P21 (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and divalent X anions or X -site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce BO5 square pyramidal units (as in ReO5) or BO3 triangular coordination (as in AsO3). Polysomatism arises through the ordered filling of [001] BO4 tetrahedral strings to generate the apatite,nasonite family of structures. [source]


Ferrocene compounds: methyl 1,-aminoferrocene-1-carboxylate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010
Christoph Förster
The title compund, [Fe(C5H6N)(C7H7O2)], features one strong intermolecular hydrogen bond of the type N,H...O=C [N...O = 3.028,(2),Å] between the amine group and the carbonyl group of a neighbouring molecule, and vice versa, to form a centrosymmetric dimer. Furthermore, the carbonyl group acts as a double H-atom acceptor in the formation of a second, weaker, hydrogen bond of the type C,H...O=C [C...O = 3.283,(2),Å] with the methyl group of the ester group of a second neighbouring molecule at (x, ,y , , z , ). The methyl group also acts as a weak hydrogen-bond donor, symmetry-related to the latter described C,H...O=C interaction, to a third molecule at (x, ,y , , z + ) to form a two-dimensional network. The cyclopentadienyl rings of the ferrocene unit are parallel to each other within 0.33,(3)° and show an almost eclipsed 1,1,-conformation, with a relative twist angle of 9.32,(12)°. The ester group is twisted slightly [11.33,(8)°] relative to the cylopentadienyl plane due to the above-mentioned intermolecular hydrogen bonds of the carbonyl group. The N atom shows pyramidal coordination geometry, with the sum of the X,N,Y angles being 340,(3)°. [source]


Two crystal forms of mesogenic bis(4,-cyanobiphenyl-4-yl) butanedioate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009
Kayako Hori
The title compound, C30H20N2O4, exhibits a nematic phase in the wide temperature range between 498.5 and 538.6,K, in spite of the short linker moiety. Two crystal forms have been found. In both forms, the molecule is centrosymmetric. Form I has a planar biphenyl group, while form II has a twisted biphenyl group with a twist angle of 34.75,(6)°. The packing modes are also different. In form I the long molecular axes are tilted with respect to each other at about 30°, while in form II the long molecular axes have an almost parallel arrangement. [source]


{4,10-Bis[2-(2-oxidobenzyl­idene­amino-,2N,O)benz­yl]-1,7-dioxa-4,10-diaza­cyclo­dodecane-,4O1,N4,O3,N10}ytterbium(III) perchlorate acetonitrile solvate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2006
Marina González-Lorenzo
In the crystal structure of the title compound, [Yb(C36H38N4O4)]ClO4·CH3CN, the ytterbium ion is eight-coordinated and deeply buried in the cavity of the dianionic Schiff base ligand. The coordination polyhedron may be described as a distorted square anti­prism that shows a twist angle of 29.5,(1)° between the two square planes. The receptor adopts a syn arrangement, with both pendent arms on the same side of the crown group, and there are two helicities (one associated with this layout of the pendent arms and the other with the conformation of the crown ring), which give rise to enantiomeric pairs of diastereoisomers, viz. ,(,,,,) and ,(,,,,). [source]


Different Photophysical Properties of Aryl-bipyridine Linked Pyrene and Anthracene

CHINESE JOURNAL OF CHEMISTRY, Issue 7 2005
Xiong Fei
Abstract 6-Phenyl-2,2,-bipyridine linked pyrene and anthracene were synthesized and their photophysical properties were measured in different solvents with different polarity. 4-Pyren-1,-yl-6-phenyl-2,2,-bipyridine (Ppbpy) showed significant solvent-dependent properities while 4-anthracen-yl-9,-yl-6-phenyl-2,2,-bipyridine (Apbpy) displayed solvent-independence, although they had similar molecular structure. Because of different twist angle between the arene and aryl-bipyridine, Ppbpy displayed intermixing behaviors of local excited state (1La and 1Lb) and intramolecular charge transfer (ICT), but Apbpy only showed the properties of local excited state 1La. [source]


X-ray Crystal Structure of a Sodium Salt of [Gd(DOTP)]5,: Implications for Its Second-Sphere Relaxivity and the 23Na NMR Hyperfine Shift Effects of [Tm(DOTP)]5,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2003
Fernando Avecilla
Abstract The X-ray structure of the sodium salt of [Gd(DOTP)]5, shows two different chelates, [Gd(1)(DOTP)]5, and [Gd(2)(DOTP)]5,, bound at either surface of a sheet formed by a cluster of hydrated Na+ ions. Each [Gd(1)(DOTP)]5, anion binds directly to four Na+ ions of this cluster through the free oxygen atoms of the phosphonate groups of the adjacent ligand, while each [Gd(2)(DOTP)]5, unit is connected to the cluster via hydrogen bonds only. The Gd3+ ions in the two moieties do not have any inner-sphere water molecules, and are eight-coordinate. Their coordination polyhedra are twisted square antiprisms, with slightly different twist angles. These m, isomers are found in the crystal structure as racemic mixtures of enantiomers. Only one set of NMR resonances is observed in aqueous solution, corresponding to an averaged m, isomer. In this crystal structure, the Na+ ions bind the phosphonate oxygen atoms of the [Gd(1)(DOTP)]5, anion at positions far removed from the main symmetry axis. This is significantly different from the binding mode(s) previously proposed to be occurring in solution between Na+ and [Tm(DOTP)]5,, based on the interpretation of solution paramagnetic 23Na NMR shifts. This could arise as a result of the effects of the cluster of hydrated Na+ ions that are present, which may hinder axial binding modes and distort lateral binding modes. Further, in the crystal structure, both types of Gd3+ centers have four second-sphere water molecules that are located at distances (4.2,4.5 Å) significantly longer than those previously proposed from the analysis of the NMRD data of [Gd(1)(DOTP)]5,. This is a result of the coordination of Na+ by these water molecules, thus preventing their direct interaction with the phosphonate oxygen atoms. However, in solution such second-sphere water molecules can interact strongly with the phosphonate ligand oxygen atoms, resulting in efficient relaxation if their binding has relatively long lifetimes (> 50 ps). Rotational immobilization will amplify this contribution, thus making it similar to outer-sphere relaxation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


The Effects of Fluorine and Chlorine Substituents across the Fjords of Bifluorenylidenes: Overcrowding and Stereochemistry

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2006
Sergey Pogodin
Abstract The bistricyclic aromatic enes (BAEs) (E)- and (Z)-1,1,-difluorobifluorenylidene, 1,8,1,,8,-tetrafluorobifluorenylidene, (E)- and (Z)-3,3,-difluorobifluorenylidene, 3,6,3,,6,-tetrafluorobifluorenylidene, and their chlorinated analogues were subjected to a DFT study of overcrowding in their fjord regions. The B3LYP hybrid functional was employed to calculate energies and geometries of the twisted conformations of these BAEs. The diastereomers E11,F2 and Z11,F2 have identical twist angles (, = 37.1°) and similar degrees of overcrowding, but differ in the degree and mode of pyramidalization, ,. In E11,F2, ,(C9) = +,(C9,) = 7.0° (syn -pyramidalization), while in Z11,F2, ,(C9) = ,,(C9,) = 1.0° (anti -pyramidalization). By contrast, in E11,Cl2 and Z11,Cl2, , = 40.6° and 42.7°, respectively. Introducing four halogen substituents results in higher twist angles: , = 40.3° in 181,8,F4 and 52.6° in 181,8,Cl4. Surprisingly, Z11,F2 is more stable than E11,F2 (,H298 = ,1.9 kJ/mol), whereas Z11,Cl2 is less stable than E11,Cl2 (,H298 = 2.2 kJ/mol). Both results are consistent with the experimental relative stabilities of these diastereomers. The unexpected stability of Z11,F2 is explained by a combination of steric and electronic effects. Calculations of Coulomb energies for point charge systems of atoms C, F, and H in the fjord regions shows stabilization of the (Z) diastereomer by ,45.5 kJ/mol. The dipole,dipole interactions in the fjord region destabilize Z11,F2 by 6.4 kJ/mol relative to E11,F2. Careful examination of the NMR spectra of E11,F2 and Z11,F2 shows, in the latter, evidence of long-range fluorine,fluorine coupling over seven bonds (11.4 Hz) and carbon,fluorine coupling over six bonds (4.8 Hz).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Improved lateral force calibration based on the angle conversion factor in atomic force microscopy

JOURNAL OF MICROSCOPY, Issue 2 2007
DUKHYUN CHOI
Summary A novel calibration method is proposed for determining lateral forces in atomic force microscopy (AFM), by introducing an angle conversion factor, which is defined as the ratio of the twist angle of a cantilever to the corresponding lateral signal. This factor greatly simplifies the calibration procedures. Once the angle conversion factor is determined in AFM, the lateral force calibration factors of any rectangular cantilever can be obtained by simple computation without further experiments. To determine the angle conversion factor, this study focuses on the determination of the twist angle of a cantilever during lateral force calibration in AFM. Since the twist angle of a cantilever cannot be directly measured in AFM, the angles are obtained by means of the moment balance equations between a rectangular AFM cantilever and a simple commercially available step grating. To eliminate the effect of the adhesive force, the gradients of the lateral signals and the twist angles as a function of normal force are used in calculating the angle conversion factor. To verify reliability and reproducibility of the method, two step gratings with different heights and two different rectangular cantilevers were used in lateral force calibration in AFM. The results showed good agreement, to within 10%. This method was validated by comparing the coefficient of friction of mica so determined with values in the literature. [source]


Bromido(,5 -carboxycyclopentadienyl)dinitrosylchromium(0) and (,5 -benzoylcyclopentadienyl)bromidodinitrosylchromium(0)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009
Yu-Pin Wang
In the structures of each of the title compounds, [CrBr(C6H5O2)(NO)2], (I), and [CrBr(C12H9O)(NO)2], (II), one of the nitrosyl groups is located at a site away from the exocyclic carbonyl C atom of the cyclopentadienyl (Cp) ring, with twist angles of 174.5,(3) and 172.5,(1)°. The observed orientation is surprising, since the NO group is expected to be situated trans to an electron-rich C atom in the ring. The organic carbonyl plane is turned away from the Cp ring plane by 5.6,(8) and 15.2,(3)°in (I) and (II), respectively. The exocyclic C,C bond in (I) is bent out of the Cp ring plane towards the Cr atom by 2.8,(3)°, but is coplanar with the Cp ring in (II); the angle is 0.1,(1)°. [source]