Debye-Scherrer Rings Research Articles

Investigation of the early mineralisation on collagen in dentine of rat incisors by quantitative electron spectroscopic diffraction (ESD).

The earliest crystallites in dentine appear as chains of "dots" in ultra-thin sections viewed by transmission electron microscopy. These dots rapidly coalesce along the longitudinal directions of the collagen microfibrils to form needle-like structures that coalesce preferentially in lateral directions to form ribbon-like or plate-like crystallites. This morphological interpretation is supported by line-scans of the corresponding zero-loss filtered electron spectroscopic diffraction patterns, which demonstrate the crystalline structure of the dentine mineral (apatite). The intensity ratio of the Debye-Scherrer rings of the characteristic Bragg-reflections (002 to 300, together with 1 or 2 unresolved reflections) shows a maximum in the region of early chain-like and needle-like crystallites, decreasing with maturation of the dentine mineral to the ribbon-plate-like crystallites. Detailed investigations using line-scans of the zero-loss filtered electron spectroscopic diffraction patterns through the dentine zone show that the intensity ratio found near the mineralisation front is repeated 3-5 times at distances of about 10-20 microns. This may represent a circadian pattern of mineralisation corresponding to light microscopically visible incremental lines in dentine.

クリーニング作用域に形成されるアルミニウム合金の微細割れの検討

Microcracks developed in cleaning action region by GTA process have been investigated using an aluminum and aluminum alloys. Although no microcracks are observed in a pure aluminum and a commercially pure aluminum, microcracks are mainly developed in the region of Al-Mg alloys where the oxide film is broken due to the cleaning action. This tendency of cracks is quite the same as the weld solidification crack. The microcracks are easily developed with the increase in EN ratio of the welding current. Since dendrites are observed on the crack surface, the microcracks is intergranular due to the solidification crack. The cooling rate in this case was estimated to be about 104°C using the size of the dendrites. The microcracks are considered to be developed due to the phenomena that the region where the oxide film is broken is locally melted owing to the high current density and the cooling rate is very high. X-ray diffraction technique made clear that the continuous vague Debye-Scherrer rings are obtained from the region where the oxide film is broken even when using a single crystal. This shows that the single crystal changes to very small polycrystals in this region and the polycrystallized depth from the specimen surface was about 100μm. Fatigue strength at 1 × 107 cycles of specimens having the microcracks is lower than that of the base metal and decreases linearly with the increase in the crack depth.

Reflection High Energy Electron Diffraction Observation of Dynamic Ion Beam Mixing Process in Titanium Nitride Crystal Growth

The initial stages of TiN crystal growth on Si substrates in the dynamic mixing method were investigated by reflection high-energy electron diffraction (RHEED) in a newly constructed ultrahigh-vacuum apparatus. The Si (001) RHEED pattern disappeared immediately after dynamic ion beam mixing started, and then was replaced by the halo pattern representing amorphous structures. The halo gradually changed to Debye-Scherrer rings representing Ti polycrystal. The results for Si (001) and (111) substrates have confirmed that the TiN crystal is controlled by the arrival ratio, Ti/N. The present RHEED pattern study has, for the first time, revealed an observable influence of the crystallography of Si substrates on TiN crystal growth.

A new neutron diffractometer with multiple detectors combining the advantages of time-of-flight and double-axis diffractometers

In this paper, the principle of a new neutron diffractometer is presented. In this diffractometer are combined the advantages of a high-resolution time-of-flight (TOF) diffractometer and some essential characteristics of a classical double-axis spectrometer (DAS), specific disadvantages of both instruments being eliminated. Its name, MARTIN (multiple-angle high-resolution time-of-flight instrument for neutrons), is derived from the particular instrumental set-up. With the MARTIN diffractometer, a neutron pulse from a narrow wavelength band (0.2–0.5 A) impinges on the sample. The diffracted radiation is registered and time-analyzed by detectors located at several scattering angles. The angular arrangement of the detectors is such that each detector samples a different portion of the diffractogram, with the portions detected by adjacent detectors partially overlapping. These partial diffractograms can be conjoined to yield the complete diffractogram of interest. This new machine has all the advantages of a TOF diffractometer: no contamination of the primary beam by higher orders, higher counting rates because of the possible utilization of the entire Debye–Scherrer ring, higher flexibility because no monochromators are needed and less strict requirements of mechanical precision as a result of the fixed detector arrangement. In addition, the use of a narrow wavelength band reduces the problem of absorption and extinction corrections in TOF diffractometry to one solvable by the well known data treatment of two-axis diffractometry. A prototype of the MARTIN diffractometer was designed for powder diffraction and installed as an extension of the TOF diffractometer at the Munich Research Reactor (FRM) in Garching, where its characteristics were tested on a powder sample of Al2O3.

The development of synchrotron x-ray area detectors for studying high pressure phase transitions

Abstract Two detector systems are currently being developed for use with high pressure cells on beamline 9 at Daresbury Laboratory. The first is a television area x-ray camera which is used for rapid alignment and specimen characterisation. The second is an imaging plate system which is being developed to obtain accurate integrated intensities from small volume powder samples. The television detector has been used to determine lattice parameters to an accuracy of 1 × 10−3 A. The measured intensities compare well with data from the same specimen collected on film. The imaging plate system was used in the same configuration as the television detector and the film. The specimens studied were La2CuO4 and InSb. The early results from this detector show a great deal of promise especially in the low photon flux region which is essential for determining accurate intensities from weak Debye–Scherrer rings. A radial integration program for summing over the whole diffraction range is being developed.

Analysis of the calcium distribution in predentine by EELS and of the early crystal formation in dentine by ESI and ESD.

Predentine is a collagen-rich extracellular matrix between the odontoblasts and the dentine with a width of about 15-20 microns. Electron energy-loss spectroscopy of rat incisors shows a significantly higher calcium content in the predentine at the predentine-dentine border than in the middle region of the predentine. At the predentine-dentine border in the dentine, the calcium and the phosphate groups combine to form apatite crystallites. Electron spectroscopic diffraction with zero-loss filtering revealed that the earliest crystallites contain only Debye-Scherrer rings of apatite, which are fewer in number and more diffuse than the diffraction rings from the mature crystallites. We therefore conclude that the early crystallites still contain lattice defects, which are annealed out to some degree with crystal growth. Electron spectroscopic imaging with zero-loss filtering also showed that the earliest crystallites are chains of dots (or small islands); they build up strands composed of islands, which rapidly acquire a needle-like character and coalesce laterally to form ribbon-or plate-like crystallites. The parallel strands sometimes appear to reinforce the macroperiod of the collagen microfibrils (67 nm) by tiny holes without any crystal-substance lined up perpendicular to the parallel strands of the crystallites.

An imaging plate system for high-pressure powder diffraction: The data processing side

The use of an imaging plate as a two-dimensional (2-D) detector removes many of the difficulties that arise in performing angle-dispersive powder diffraction at high pressures in a diamond-anvil cell. Due to the 2-D nature of the imaging plate, a substantial part of each Debye Scherrer ring is intercepted and recorded. The averaging of the intensities around a ring so as to create a conventional one-dimensional (1-D) powder pattern results in a significant improvement in counting statistics and powder averaging, both severe problems in high-pressure diffraction due to the very small sample volumes involved. For an accurately known plate geometry the 2-D to 1-D conversion is straightforward; however, considerable complications arise when inaccuracies in plate to sample distance, plate orientations, poor powder averaging/preferred orientation, and the presence of diamond Bragg spots are considered. The current status of the software used to analyze the imaging plate data is presented along with test data to illustrate its use.

Evalution of X-ray diffraction data from protein crystals by use of an imaging plate

A system has been developed which uses an imaging-plate diffraction apparatus to obtain structure factors for protein crystals. The latter is connected to a graphics workstation through an Ethernet. Pixel data from an imaging plate are transferred via the Ethernet to a workstation and processed to give the structure factors. The quality and precision of the diffraction data were examined from the point of view of spatial uniformity, linearity with exposure, decay with time, and reproducibility. X-rays from an 55Fe source and Debye-Scherrer rings from Si powder were used for calibration purposes. Finally, diffraction data were obtained and evaluated for lysozyme and cytochrome c-553 using this system. The results were satisfactory in terms of sensitivity and precision.

X-Ray Analysis of Stress in a Localized Area by Use of Imaging Plate

AbstractFor determination of stress in a localized area, we combined a modified single exposure technique and the imaging plate, which is an x-ray digital area detector. With the, single exposure method, stress value is obtained from lattice strains in two directions with a single incident x-ray beam directed at an oblique angle. However, since diffraction data around a whole Debye-Scherrer ring was used in this study, a stress value can be accurately determined in comparison with the single exposure method. We observed the DS ring by use of the imaging plate with requiring only a short exposure time. Lattice strains in many directions on a DS ring were measured by an image analyzer connected to a computer; we verified the effectiveness of this method.

Determination of the Orientation Distribution Function From Arbitrary Diffraction Data

A method proposed by Bunge in which we assume a fit between the theoretical ODF and the isolated expetal points was used to calculate the ODF from experimental data chosen in an arbitrary way in a pole figure and an inverse pale figure space. In particular, this technique was used to obtain the ODF from the measurements of three, two and one pole figures, from the data obtained using the reflection technique only or transmission technique only, from inverse pole figures and from the photo showing the Debye-Scherrer rings. Various tests described in this paper allows us to suggest an empirical rule indicating that the number of experimental data points should be three times higher than the number of required series expansion coefficients of the ODF. In addition, other factors, for instance, the strength of texture and the distribution of experimental points are also important.

Advantage of Electron Spectroscopic Diffraction on Calcified Tissue Sections

Different stages in the mineralization of calcified tissues can be investigated by electron diffraction. A disadvantage is the strong background below the Debye—Scherrer rings caused by the large massthickness of calcified products and the high ratio (≃ 3) of the inelastic—to—elastic scattering cross—sections of the embedding material. Therefore, a large fraction of the background consists of inelastically scattered electrons with energy losses. The electron spectroscopic diffraction (ESD) mode of an energy—filtering microscope (ZEISS EM902) allows to record diffraction patterns using only the zero—loss electrons which consist of the primary beam, Bragg diffracted electrons and a smaller fraction of elastically scattered electrons between the Debye—Scherrer rings by thermal—diffuse scattering. Small—area diffraction patterns with different camera lengths are generated at the filter—entrance plane and the zero—loss electrons are selected by a slit in the energy—dispersive plane behind the Castaing—Henry filter lens.

Calculation of the crystal orientation distribution function from synchrotron radiation experimental data

Series-expansion coefficients for an orientation distribution function (ODF) of cold-rolled aluminium sheet were calculated from the intensity of Debye–Scherrer rings obtained in an experiment using synchrotron radiation. Calculated and observed pole figures demonstrate that a sufficiently good approximation to the ODF is obtained from coefficients calculated to l = 8.

Electron diffraction studies of supersonic jets. 8. Nucleation of various phases of sulfur hexafluoride, selenium hexafluoride, and tellurium hexafluoride

Old microcrystals of SF/sub 6/, SeF/sub 6/, and TeF/sup 6/ are condensed when the gaseous hexafluorides in monatomic carriers flow supersonically through aminiature Laval nozzle. Electron diffraction records of the condensates display strong Debye-Scherrer rings. The diffraction patterns depend markedly upon the carrier gas and expansion conditions. For the hexafluorides of sulfur and selenium the well-known body-centered plastic cubic phase forms if the molecular weight of the carrier gas is low and the subject mole fraction exceeds several percent. A phase II of low symmetry begins to appear only at low mole fractions of SF/sub 6/ and requires a carrier at least has heavy as argon. Phase II appears for SeF/sub 6/ with argon carrier under all conditions examined and with neon under extreme conditions. It appears readily even with helium in the case of TeF/sub 6/, provided the subject mole fraction is comparatively high. At lower mole fractions and total pressures another, as yet unidentified, phase III of TeF/sub 6/ is produced. Patterns of phase II are well accounted for by the triclinic lattice P1, Z = 3. Refinements based on this space group, for the two compounds yielding nearly pure phase II, led to the following cell constantsmore » (3sigma): SeF/sub 6/ (T < 140 K), a = 14.51 (8) A, b = 8.22 (3) A, c = 4.92 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/; ..beta.. = 93.7 (4)/sup 0/, ..gamma.. = 88.14 (4)/sup 0/; TeF/sub 6/ (T < 160 K.), a = 14.99 (7) A, b = 8.53 (3) A, c = 5.06 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/, ..beta.. = 93.5 (3)/sup 0/ = 88.9 (3)/sup 0/.« less

Raman Study of Silicon Small Particles

The particle-size dependence of Raman spectra of gas-evaporated silicon small particles, whose size distribution is well described by a log-normal distribution function, is reported in connection with their electron diffraction patterns. Although a diamond structure is confirmed by the Debye-Scherrer rings for the samples with an average particle size from 70 to 220 A, the Raman spectra are rather complex; the spectra are resolved into a new surface mode and three known modes (LA, TO and allowed-TO ones) in a range of 250 to 600 cm -1 . A disadvantage of the present theoretical studies relating to the finite-size effects of microcrystalline silicon is pointed out.

Directly RF-sputtered γ-Fe&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;O&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;thin films

RF-sputtered γ-Fe 2 O 3 thin films have been proposed for obtaining high bit densities in digital magnetic recording. However, those reported methods of preparation for γ-Fe 2 O 3 films involve RF reactive sputtering of Fe or Fe 3 O 4 followed by heat treatments for oxidation and reduction. Better control of their properties and savings in processing time and cost are attained by directly sputtered γ-Fe 2 O 3 films. We present results of measurements of the structure and magnetic properties of γ-Fe 2 O 3 films which were directly sputtered from a Fe 3 O 4 target on to glass, Al, and Si substrates. X-ray diffraction patterns obtained for these films showed the characteristic γ-Fe 2 O 3 peak distribution. Electron diffraction also exhibited Debye-Scherrer rings of the γ-Fe 2 O 3 structure. The in-plane coercivity ranged from 500 to 650 Oe. with squareness of 0.31 to 0.44 and the perpendicular coercivity ranged from 750 to 1000 Oe. with squareness of 0.70 to 0.82. The directly RF-sputtered γ-Fe 2 O 3 appears to have perpendicular magnetic anisotropy.

Liquid structure under shear: Comparison between computer simulations and colloidal suspensions

Simulated scattered light intensity plots are calculated for a soft sphere inverse-12 system subjected to a shear and are compared to experimental plots for a colloidal suspension under approximately equivalent conditions. The simulated plots were obtained by a Fourier transform of the radial distribution function. The two sets show points of striking similarity: The Debye–Scherrer rings become elliptical when both systems are subjected to the shear, and the light intensity around the rings is a function of polar angle. An interesting feature is the degree to which the experimental plots display non-Newtonian characteristics of the suspension. Overall, the work is a direct comparison of the results of a computer simulation with real experimental data. Suggestions for future work are given.

Interpretation of the fading of diffraction patterns from organic substances irradiated with 100 keV electrons at 10-300 K

The fading curves of Debye-Scherrer ring intensities have been recorded for evaporated films of some aliphatic and aromatic compounds at temperatures between T s =14-66 K and room temperature. The lowest real specimen temperature T s was calibrated by the condensation of different gas atoms and depends on the current density used, which has to be raised with increasing resistivity to radiation damage. The fading curves for the lowest specimen temperature were compared with a theory of Clark et al. modified by a multiple-hit model. By fitting the theory to experimental results, values of the cross-section σ for a single hit, the mean number m of hits necessary to destroy a sensitive unit and the ratio b of the damaged to the undamaged structure amplitude of a unit cell can be established. There are considerable differences in these quantities for different compounds. The temperature dependence of σ for tetracene and other compounds can be explained by an activation energy of the order of a few tens of one meV.

Coagulation of polymer–Cu2 complexes in polymer films and its application for producing semiconducting CuI surface layers

In poly(vinyl alcohol) and polyacrylamide films containing the corresponding polymer–Cu2+ complexes, the reason why the films may gain surface electrical semiconductivity as high as 10−3 Ω−1 when treated with acetone solution of iodine was investigated. Optical and scanning electron microscope observations indicated that the coagulated polymer–Cu2+ complexes favor the appearance of the high conductivity and that the state of coagulation depends on the anions of the copper salts used as well as two parameters, F1 ≡ [Cu2+]/[MU] and F2 ≡ [OH−]/[Cu2+], where [MU] is the molar concentration of monomeric units of the polymer and [OH−] is that of hydroxide ions added. The effectiveness of the anions in causing coagulation decreases in the order of SO42− > Cl− > NO3− ≈ Br−. The whitish substance that appears on the film surface after the iodine treatment gives x-ray Debye–Scherrer rings characteristic of γ-CuI. The γ-CuI surface layer adheres to the film rather firmly, at least in polyacrylamide, and is responsible for the conductivity. By controlling the state of coagulation of the complexes and hence the formation of the γ-CuI surface layer, we have produced films with anisotropic surface electrical semiconductivity, i.e., σ∥ ≈ 10−4 Ω−1 and σ∥/σ⊥ = 1 ˜ 103. Optical and ESR spectra are also obtained to understand the mechanism of γ-CuI formation and to clarify the optical properties of the films.

Electron diffraction studies of the peptidoglycan of bacterial cell walls

Peptidoglycan of the gram-positive bacterium Lactobacillus plantarum was adsorbed onto hydrophilic crystalline films of graphitic oxide. Destruction by radiation damage was reduced by using a device which permitted scanning of the specimen for several hours through a focussed electron beam of low current density (2.5 X 10(-5) A/cm2). In additition to the sharp Debye-Scherrer rings caused by graphitic oxide, peptidoglycan causes a diffuse Debye-Scherrer ring in the region of 4.5 A. This can be interpreted as the packing periodicity of the peptidoglycan within the planes of the peptidoglycan sacculi.

Collimation correction for non-isotropic small-angle X-ray scattering curves from lamellar systems

A collimation-correction method is presented which is suitable for scattering curves of large lamellae with a partial disorientation of their axes. If it is assumed that the orientation of the lamellar multilayers can be characterized by a mosaic spread, the intensity at a given scattering angle is limited to a defined arc on the corresponding Debye-Scherrer ring and the distribution of the intensity along this arc depends on the distribution function of the multilayer orientations. It is further assumed that this orientation distribution function can be approximated by a Gaussian (normal distribution). Its width can be estimated from a short-time pin-hole collimated X-ray film exposure. Thus, an additional condition has to be inserted into the smearing integral equation, which is solved using the iterative method of Lake [Acta Cryst. (1967), 23, 191–1943]. The procedure has been successfully tested on lamellar intensity functions from models and thereafter has been applied to the small-angle X-ray scattering curves of partially oriented erythrocyte ghost membranes.