Laue Spots Research Articles

Screw dislocation lines in lysozyme crystals observed by Laue topography using synchrotron radiation

Laue topography of the tetragonal crystals of hen egg-white lysozyme has been carried out using synchrotron radiation. Straight-line images extending from the core part to the growth fronts were observed and interpreted as dislocations. They had the displacement vectors parallel to the line; they are similar type of dislocations common to the crystals grown from solutions. The Laue spots showed uniform distortion. The water filter 10 mm thick was effective in avoiding radiation damages.

Laue crystallography: coming of age

A renewed interest in the Laue diffraction technique has been brought about by the development of new, more intense and brilliant synchrotron sources along with their insertion devices such as wigglers and undulators, and by the prospect of using these sources to study structural dynamics by time-resolved crystallography. Theoretical studies during the past decade have identified unique features of the polychromatic diffraction geometry and greatly improved our understanding of the Laue method. This led to innovative approaches to Laue data processing and its software implementation. Most of the problems in Laue data processing, considered for a long time to limit the applicability of the technique, have been solved. Significant advances have also been made in the development of synchrotron sources, beamline optics and instrumentation, and the X-ray detectors. Static Laue experiments yield structure amplitudes that equal those from monochromatic data in quality. When coupled with careful consideration of data-collection strategies and reaction initiation in crystals, a series of successful time-resolved Laue experiments on biological systems have been conducted. These have revealed information on structural dynamics inaccessible to any other conventional diffraction method. These static and time-resolved experiments demonstrate that the Laue method is coming of age. They also suggest avenues for future improvements: a correct treatment of finite mosaic spread and the associated energy width of Laue spots; consideration of diffuse scattering; and determination of intermediate structures in time-resolved experiments in which those intermediates do not attain a high concentration.

Elasticity effects on domain coarsening of the lamellar-gyroid transition observed in a nonionic surfactant system.

The coarsening process of the gyroid phase of a nonionic surfactant system is investigated by time resolved small angle neutron scattering (SANS) and small angle neutron Laue diffraction techniques. The time evolution of SANS patterns shows anomalous coarsening of the gyroid domains. The observed Laue spot from a gyroid domain becomes elongated along the radial direction with the elapse of time and at a certain time the elongated spot is split into two spots. The results can be interpreted as follows. During the coarsening process, mismatch of the lattice orientation at the domain boundary brings strong stress to the gyroid domain, resulting in the distortion of the domain. The stored stress in the domain finally brings splitting of the gyroid domain. The elastic and fragile nature of the gyroid domains composed of the "soft matter" is responsible for the anomalous coarsening.

Neutron Structure Analysis and Structural Disorder of Poly(p-phenylene benzobisoxazole)

On the X-ray fiber diagram of poly(p-phenylene benzobisoxazole) (PBO), the diffuse streak scatterings are observed along the first and third layer lines, while Laue spots can be observed on the second and fourth layer lines. This shows that the molecular heights of PBO are disordered by a half of the fiber period. Therefore, the cell parameter c reduces to a half of the fiber period, 12.05 A. Furthermore, all the reflections observed on the X-ray fiber diagram can be indexed by the one-chain unit cell with parameters a = 5.651 A, b = 3.570 A, and γ = 101.4° (at 295 K). Neutron diffraction measurements were made on the equator at 17, 100, 200, and 295 K, and the structure analyses were made. The half-widths of the reflections do not depend on the temperature. This shows that the crystallite size and lattice distortion are independent of the temperature. The temperature dependences of the unit cell dimensions and temperature parameter are small in comparison with those of polyethylene, one of the flexible polymers. This may reflect the rigidity of the PBO molecule.

Laue and Kossel Diffraction on Quasicrystals by Means of Synchrotron Radiation

Laue experiments using synchrotron radiation have been carried out on quasicrystalline samples mainly with decagonal symmetry. Apart from Laue spots, Kossel lines and diffuse scattering have been observed on the X-ray film simultaneously. High spatial resolution was achieved by the positioning of the X-ray film at a distance of about 350 mm from the sample. Conclusions about the real structure and the crystal quality could be drawn using information obtained from the appearance of the Kossel lines, and the shape and the splitting of the Laue spots, respectively. The dimensions of the mosaic blocks and their tilting behaviour for one of the samples under investigation have been determined.

X-ray topographic investigation of tungstate flux-grown KTiOAsO4 crystals

White-beam synchrotron radiation and Lang topographic investigations of non-linear optical crystal KTiOAsO4 have been carried out. It is shown that domains and growth striations are primary planar defects in tungstate flux-grown single crystals. By selecting the wavelength to activate anomalous scattering effect near the absorption edge of the As atom, antiparallel ferroelectric domains are revealed, and in reflection pairshkl and\(\overline {hkl} \), the domains demonstrate contrast reversal. The differences in integrated intensity from a pair of opposite domains are also calculated and the harmonics in a Laue spot are given. Finally, the domain wall configurations are discussed in terms of the structural characteristics of KTiOAsO4.

Real Time Observation of Material Deformation Processes by Synchrotron White Beam X-ray Topography

ABSTRACTAn experimental apparatus which exploits synchrotron white beam X-ray diffraction topography has been developed to perform real time in situ observation of deformation processes of single crystals. The apparatus consists of a fully automated and remotely controlled mini-tensile device and a CCD based X-ray imaging detector with associated video system. Both tensile data and X-ray topographic images are recorded simultaneously. The materials under study include single crystals of Si, and single crystals or bicrystals of the refractory metals W and Mo. The deformation processes of these crystals have been studied by monitoring a selected transmission Laue spot while the specimen is mechanically cycled by loading and unloading. The X-ray images have been captured by a frame grabber and recorded via a VCR. Several phenomena have been observed, including bending contours, strain concentrations, reversible anelastic effect and microyielding. The observed stress relaxations are correlated to microstructural variations shown by X-ray topography. The stability of low angle grain boundaries in bicrystals; and the effect of high strength and toughness coatings on the deformation of single crystal substrates was investigated.

Computerized Linear Coordinate Nets in Crystallography

On the basis of the gnomonic projection, a new concept, the linear coordinate net (LCN) of crystals, is presented. With such nets, the Miller indices of Laue spots and the orientation of the crystal can be read directly without any calculation or graphical operation. These nets can be constructed with an IBM personal computer. In this paper, the principle and formulas, the computer program for constructing the nets and the applications of the LCNs are described. The main applications are when the incident X-rays are in a low-indices direction or are perpendicular to a plane with low Miller indices.

Submicron Resolution X-Ray Strain Measurements On Patterned Films: Some Hows And Whys

AbstractAs interconnect technology moves deeper into the submicron realm, the physics governing the mechanical behavior, hence the reliability of metal lines changes. Events at the level of individual grains become more important. One would like to be able to measure the strain and orientation of single grains, and the distribution of strain across a grain. Such data may help us understand such effects as sunken grains, the erratic occurrence of stress voiding and Blechlength effects in electromigration. To get this information, techniques involving X-ray diffraction with submicron beams are being developed. These experiments involve detecting Laue spots from selected areas and energy-analyzing them to find the strain tensor. Motivations for such measurements, the specifications for a useful instrument, some designs now being developed and the intrinsic limitations of these approaches will be discussed. Design issues in the choice of focussing optics and energy measurement will be highlighted with calculations of how the Laue spots would look for different conditions of crystal perfection.

Modification in the Debye-Waller factor and bragg law, and examination of the dynamical X-ray diffraction due to them

Based on an experimental result on disappearance of the Laue spots of the downward x-ray diffraction (2 θB∼90°. Hereafter, abbreviated as DXD.) in solid helium a radically modified Debye-Waller factor and a modified Bragg law, considering the recoil scattering and its Doppler effect, could be obtained. Since kBΘD≪ER (recoil energy) in solid helium in contrast with the reverse inequality in almost all materials, the fraction of recoil-free diffraction is extremely less than one which is one of main causes of disappearance of the Laue spots of the DXD. The difference of wave-length in Pendelloesung beat 1.4 · 10−6 Aby using Kato-Lang’s fomula from the (200) plane in GaAs which occurs by slight frequency shifts of incident X-ray becomes in order of 0.5· 10−6 A derived from a modified Bragg law. This agrees very well with the experimental values of GaAs [1].

Prominent peculiarities of X-ray diffraction of solid helium

Since3He and4He atoms are the lightest stable mono-atoms with atomic number 2, they cause a variety of macroscopic quantum effects, including large zero point vibrations in liquid and solid phases. Some quantities relevant to X-ray diffraction of solid helium, i.e., the atomic-scattering factor, mass-absorption coefficient, the reciprocal of which is the characteristic length defined by absorption and the extinction distance etc., show either larger or smaller values by approximately two orders of magnitude compared with 3d transition metals. An incidental disappearance of Laue spots due to the downward X-ray diffraction of solid helium (2θB = 90°) could be explained by two factors. One is that the fraction of recoil-free emission is weakened by the great ratio of the huge recoil energy to the phonon energy through the zero-point energy in the Debye-Waller parameter. The other is that the great difference in the linear scatterer density in downward diffraction from that in forward diffraction results from the irradiation of a line-focus X-ray beam to take section topographs weakens the downward X-ray diffraction. The dislocation line of solid helium could not be observed with sharp contrast. Considering the two-orders higher magnitude of the extinction distances and the high dislocation density of more than 2.6· 105cm−2, dynamical X-ray diffraction seems to lose validity.

An Ultra-Low-Temperature Diffractometer Based on an 3He–4He Dilution Refrigerator used for Synchrotron-Radiation X-ray Diffractometry and Topography

The direct observation of crystal structure at ultra-low temperatures helps better understanding of phase transformations and phase stability. Two sets of 3He-4He dilution refrigerators with a top-loading facility were installed at BL-3C2 and 6C1 of the Photon Factory. The first is used exclusively for topography of quantum crystals of solid 3He and 4He for studies of lattice defects. Typical examples of topographs that indicate an annealing effect of solid helium, understood in terms of a quantum tunneling, are presented. The disappearance of downward diffraction Laue spots (2θB = 90°) is discussed on the basis of the temperature and other factors in solid helium. The second refrigerator is used for X-ray diffraction studies of crystalline solids. A splitting of the Laue spots from Cs2NaHoCl6 below 150 mK, giving evidence of a cooperative Jahn–Teller transition of the first kind at the lowest transition temperature ever observed, is briefly explained as an example of diffractometry.

Development of a microarea diffraction system by polychromatic synchrotron radiation with the Laue method

Microarea diffraction equipment has been developed with a micropinhole and an imaging plate using the Laue method combined with polychromatic synchrotron radiation. The crystal structure of 8 μm diam area of olivine [(Mg,Fe)2SiO4] grain included in a thin section of meteorite was successfully refined based on the intensities of Laue spots.

Low temperature diffractometer below 1 K by a 3He‐4He dilution refrigerator used for synchrotron radiation x‐ray diffraction

The observation of changes in the crystal structure at low temperatures plays very important roles in gaining a better understanding of mechanism of the phase transformation and stability of the phase as a ground state. For these purposes, two sets of 3He‐4He dilution refrigerators with a top loading facility were installed at BL‐3C2 and 6C1 of the Photon Factory. The former is used exclusively for taking topographs from quantum crystals of solid 3He and 4He for studies of lattice defects. Typical examples of topographs, which indicate an annealing effect of solid helium which might be understood from a viewpoint of a quantum tunneling effect, are presented. The latter refrigerator is used for studies of crystalline solids by x‐ray diffraction. A splitting of the Laue spots of Cs2NaHoCl6 below 150 mK, giving evidence of a Jahn–Teller transition of the first kind, which is the lowest transition temperature ever detected, was observed as a new peculiarity of the phase transition at ultralow temperature.

The Evolution of X-ray Analytical Instrumentation at Rigaku Corporation

Soon after Von Laue's experiment of X-ray diffraction in 1912, a similar experiment was conducted in Japan by Prof. Terada at University of Tokyo. He made direct observation of Laue spots from rock-sault on a fluorescent screen. In 1914, Prof. Nishikawa also at University of Tokyo photographed Laue spots of spinel. The X-ray generator employed was one designed for medical use. The first X-ray diffractometer in Japan was fabricated in the 1920s at the Institute of Physical and Chemical Research, It was designed with reference to Bragg's spectrometer using an ionization chamber as the X-ray detector.In 1932, X-ray generators and cameras were manufactured by Rigaku Denki Mfg., the predecessor of the present Rigaku Corporation, Shimazu Mfg. and some other few companies. X-ray tubes at the time were Coolidge type demountable tubes.

Evidence for a Jahn-Teller distortion of Cs2NaHoCl6 at 150 mK observed by X-ray diffractometry

By means of SR X-ray diffractometry, cooperative Jahn-Teller distortion as a structural phase transformation of the first kind is directly confirmed by a splitting of Laue spots. It is understood that the degenerate ground state of a nonmagnetic doublet (Γ3) of Ho3+ in a cubic Ho-elpasolite, Fm3m(Oh5), at least above 600 mK, is lifted up by a distortion below 150 mK, which was predicted by a splitting of the NQR spectrum and anomalies in the specific heat and magnetic susceptibility. This structural transformation shows not only the lowest transition temperature up to now, but also the greatest hysteresis specified by a Schottky-type excitation. The magnitude of the relative distortion (Δ1/1) has been roughly estimated to be on the 2.0 · 10−3 order of magnitude, which is much larger than the predicted value obtained from a point charge approximation. The pecularities of this transition are discussed from the viewpoint that the general theory of a structural transformation, established convincingly at high temperatures could not be easily applied.

Molecular Dynamics Simulation of Nucleation and Growth of a Binary Quasicrystal

Abstract The quasicrystal structure is considered to be a new type of ordered phase because its Fourier transform has Laue spots with icosahedral symmetry, which is inconsistent with crystal structure. Computer simulation of the formation process of a quasicrystal was performed by the molecular dynamics method. On the basis of the Strandburg type of quasicrystal model, we developed an algorithm of the formation process of binary quasicrystal reflecting the procedure as realistically as possible. The Fourier transform of some of the obtained structures has shown decagonal symmetry although the spots are rather diffused. It has been shown that the potential parameter and experimental condition should be limited to produce a perfect quasicrystal structure.

Standard stereographic diagrams and indexing of X-ray Laue diffraction spots of an icosahedral quasicrystal

White-beam synchrotron-radiation X-ray topographs of the Al62Cu25.5Fel2.5 icosahedral quasicrystal (IQC) have been taken for different specimen orientations. Standard stereographic projection diagrams along the two-, three-, and fivefold zone axes of the IQC have been calculated by the cut-and-projection method. The total structure factor S(g parallel-to) has been calculated with the simple lattice model for each reciprocal vector g with indices n(i)* lying in the range - 8 less-than-or-equal-to n(i)* less-than-or-equal-to 8 and reflections with the highest S(g parallel-to) values have been selected to simulate the geometric distribution of the Laue spots for a given incident-beam direction. On the basis of standard diagrams of simulated Laue patterns, all the strong diffraction spots have been indexed successfully. For the specific experimental arrangement and the characteristics of the synchrotron-radiation source, the mean intensities of the diffraction spots have been calculated and are in agreement with the experimental ones.

Determination of the <i>c/a</i> Ratio of a Submicrometer-Sized Crystal of Tetragonal Barium Titanate by the Synchrotron Radiation

The tetragonality of submicrometer-sized crystals of barium titanate, BaTiO3, has been investigated by the ultramicro single-crystal X-ray diffraction technique using synchrotron radiation. The c/a ratios have been determined using the splitting of Laue spots due to twinning to be 1.0072 (2) and 1.0106 (6) for crystals with conversion diameters of 0.56μm and 10μm, respectively. The c/a ratio of the 10μm crystal is approximately the same as that of the bulk crystal, while it is significantly small for the 0.56μm crystal, indicating that the size effect on the tetragonal-to-cubic phase transition is remarkable in the submicrometer region. No clear splitting due to tetragonal twinning was observed for the crystal with a conversion diameter of 0.25μm, suggesting that the critical size for the transition is close to this size.

Low-symmetry metastable phases formed during crystallization of the metallic glass Pd80Si20

Low-symmetry metastable phases with planar defects of the metallic glass Pd80Si20 are observed at the initial stage of crystallization. Since the reciprocal points are stretched into rods in the direction perpendicular to the planar defects, when the reciprocal rods intersect the Ewald sphere, electron diffraction patterns with cross-grating bands will be obtained. Geometrically, the indexes of these diffraction spots can be directly obtained from these diffraction patterns. The structure parameters of these low-symmetry phases are analyzed with the aid of high-order Laue zones and Laue spots. The appearance of these metastable phases reveals that the crystallization of the metallic glass Pd80Si20 is a complicated and composition dependent process, and the lattice parameters of these metastable phases are affected by the local composition.