Single Diffraction Pattern Research Articles

A method for determination of the rhombohedral angle of SbSn

A method is suggested which allows several independent determinations of the rhombohedral angle using data from a single diffraction pattern. This is applied to the intermetallic compound SbSn.

Foil Thickness Determination from Single Crystal Diffraction Patterns

Foil thickness measurements are necessary for determining crystal volumes, which in turn are needed to calculate defect densities for dislocations or point defect clusters or for determining interparticle spacings. The most generally applied technique for obtaining the foil thickness is the trace method wherein the trace of a known plane (slip trace, stacking fault, grain boundary, etc.) must be determined, its projected width on a micrograph measured, the precise crystal orientation calculated from a diffraction pattern and the thickness calculated from simple trigonometric relationships. If no traces are obtainable on an image, an alternate method uses extinction contours: a perfect wedge-shaped crystal is set at the Bragg angle, and the number of white fringes from the edge of the foil in a bright-field micrograph (or dark fringes in a dark-field micrograph) counted and multiplied by the extinction distance (which must be accurately known) for the particular reflection involved.

Beugung im inhomogenen Primärstrahlwellenfeld. I. Prinzip einer Phasenmessung von Elektronenbeungungsinterferenzen

In addition to the amplitude information, phase information can also be obtained from a generalized diffraction experiment (in spite of the inability of the detector to observe phases directly) on condition that the primary ray can be controlled in a defined way. A single diffraction pattern suffices for the determination of the phases except in the case of a centre of symmetry in real space, and the combination of at least two patterns removes this ambiguity.

Occurrence of Olivine in a Type I Carbonaceous Meteorite

A REPORT of the discovery of olivine in the Orgueil carbonaceous meteorite1 aroused considerable scepticism2,3. The identification was based on selected area electron diffraction patterns obtained from two mineral fragments observed during an electron microscope examination of a powdered meteorite specimen. Because, with the electron microscope in use at that time, it was only possible to examine particles in the orientation which they had arbitrarily taken up on the specimen support film, each diffraction pattern gave only limited information about the unit cell parameters and space group of any individual unknown mineral. The possibility of using such restricted data to identify mineral species rests on the fact that many minerals develop pronounced and specific faces, either by growth or cleavage, so that different fragments of the same mineral tend to lie in a common orientation, and thus to exhibit the same type of single crystal diffraction pattern in the electron microscope. The match between patterns from terrestrial olivine samples and those from olivine in Orgueil was good, but it was clearly desirable to put the identification on a firmer basis, if possible, by obtaining for a single mineral particle the full complement of unit cell parameters and the space group.

EFFECTS OF CHANGES IN SOME SOLVENT PARAMETERS ON CARBOXYPEPTIDASE A IN SOLUTION AND IN CROSS-LINKED CRYSTALS

Quiocho and Richards1 have shown that oii treatmeilt with the bifunctional reagent glutaraldehyde, single crystals of the enzyme carboxypeptidase A become completely insoluble. The effect appears to be due to intermolecular cross-linking which provides ani effectively infinite three-dimensional4network. The material gives single crystal X-ray diffraction patterns very similar to those obtained with the untreated protein. Both the native and cross-linked crystals have demonstrable catalytic activity for hydrolysis of the protected dipepticle substrate carbobenzoxyglycyl-L-phenylalanine (CGP). More recent studies have begun to define the enzymic properties of both the crystalline and amorphous enzyme.2 Access of substrate (CG1P) to the interior of the crystals is not limited by diffusion if the minimum crystal dimension is 5-10 t or less. The substrate concentration required to reach half-maximal activity is roughly the same for all forms of the enzyme. The shapes of the velocity versus substrate concentration curves for the solid samples of the enzyme differ from those in solution, but they are still indicative of multiple substrate-binding sites. In passing from the soluble enzyme to very small native crystals at low ionic strength the specific activity measured with CG1' decreases by a factor of about 300. The cross-linking reaction per se results in a further decrease inactivity of onily a factor of 2.

Erratum: “Lattice Modulation in the Ordered Alloys with Long Period Studied by X-Ray Diffraction. I. Au3Cd”

Au 3 Cd which is an ordered alloy with the one-dimensional regular anti-phase domain structure exhibits an asymmetry in intensity of components of each pair of split superlattice reflections in X-ray single crystal diffraction patterns, the splitting being caused by the presence of the periodic anti-phase domains. The nature of lattice modulation revealed by this intensity asymmetry has been investigated in detail. Fourier synthesis has been made using ( h 0 l ) type reflections and the crystal structure has been refined taking into account the information obtained from the synthesis. The result shows that the modulation is nothing but the periodic displacements of atoms from the normal positions, gold atoms being displaced away from the anti-phase domain boundaries by 0.015±0.005 A and cadmium ones being displaced in the opposite directions by 0.028±0.005 A. This type of lattice modulation seems not to contradict the idea suggested by Sato and Toth that the ordered alloys with long period are stabilized ...

On the Anti-Phase Domain Structure of the Ordered Phase CuAu3

A model for the anti-phase domain structure of CuAu 3 is proposed which can account well for the particular feature of the superlattice reflections observed by Hirabayashi in his single crystal X-ray diffraction pattern. In this model, the imperfectly ordered lattice consists of anti-phase domains with the shape of dodecahedron. Domain boundaries are {110} planes, across which direct contact between like atoms takes place more frequently than inside domains. The shape and size of domains may considerably be irregular in the actual lattice.

Electron Microscopy of Beta-Beryllia

THE development of β-beryllia1 has been observed in the electron microscope. Fine chips of beryllium oxide obtained by grinding single crystals in a mortar and supported on a carbon substrate were examined in an EM–6 electron microscope. Most of the transparent chips fracture along prism planes and these yielded single crystal diffraction patterns which were readily indexed as the normal hexagonal structure of α-beryllia. Transformation to the high-temperature form was accomplished by defocusing the illuminating electron beam and allowing a more intense beam to strike the sample. This develops a finely shattered texture in the crystal. The evidence that the tetragonal structure of β-beryllia is formed is indicated by the appearance of new rings or diffraction spots from β-beryllia that are superimposed on the spot diffraction pattern of single crystal α-beryllia. In particular there are observed the (110) and (310) reflexions of β-beryllia with d-spacings agreeing within experimental error with those previously reported1; simultaneously the (002) of α-beryllia is commonly absent. Occasionally extra diffraction rings appear; these can be indexed if one presumes that beryllium carbide is formed by reaction between the beryllium oxide and the carbon substrate.

The production of a single slit diffraction pattern by reflection

The production of a single slit diffraction pattern by reflection

The single crystal diffraction patterns of silicon

A triple-crystal diffractometer is used to study the single crystal diffraction patterns of Si (111), (220), (333) and good agreement with the dynamical theory of X-ray diffraction on perfect single crystals is found. This proves the possibility of using Si single crystals as in X-ray spectroscopy for a double-crystal spectrometer with a high resolving power as well as for studying very narrow diffraction patterns by means of a triple-crystal diffractometer.

Single crystal diffraction patterns of germanium. Part II

The rocking curves of Ge (111), (220), (333) for CuKα1 radiation were measured by means of the triple-crystal diffractometer. Perfect silicon single crystals, cut parallel to the (111) plane were used in the monochromator part of the triple-crystal diffractometer. The results prove the suitability of such a monochromator for studying diffraction patterns.

Cell dimensions and space group of bismuth(I) chloroaluminate

The cell dimensions and interplanar spacings of bismuth (1) chloroaluminate are determined from crystals grown from melt under helium. Single crystal diffraction patterns show the c rystal to be rhombohedral. The hexagonal unit cell of BiA1C1/sub 4/ is a = 11.855 plus or minus 0.003 and c = 29,991 plus or minus O.OO9A, corresponding to the rhombohedral cell a = 12.109 plus or minus 0.002A and alpha = 58 deg 29' plus or minus 2 plus or minus . Precession patterns of the hexagonal levels hol, hll. and h21 show the systematic absences hnl (absent if 1 plus or minus 2n) and hkl (absent if -h + k + 1 plus or minus 3n). The space groups consistent with these absences are R3c and R3c with the probable space group being R3c. (N.W.R.)

Single crystal diffraction pattern of germanium

The diffraction pattern for the (111)-reflection of germanium was measured by means of the three-crystal arrangement and compared with dynamical theory. The results obtained indicate the possibility of using germanium crystals for precise measurements in X-ray spectroscopy.

Single crystal diffraction pattern of germanium

Single crystal diffraction pattern of germanium

Experimental Study of the Slit Function of an Ebert Spectrometer in the Visible and Near-Infrared*

The slit function of an Ebert spectrometer has been measured with different f numbers at the wavelength of the 0.5461 μ Hg line and the 2.05 μ He line. It is shown that the slit function changes from a single slit diffraction pattern to a Gaussian and finally to a triangular function for increasing slit width.

The use of the stereoscopic tilt device of the electron microscope in unit-cell determinations

An improved method is detailed, making use of electron diffraction of individual crystals in the electron microscope, for determination of the unit-cell dimension most nearly parallel to the electron beam. A series of diffraction patterns is recorded from a crystal tilted through known angles by the device normally used for making stereomicrographs. One of these patterns serves as a datum, for location on each of the others of the centre of its almost circular Laue zones. A new method is described for calibration of the instrument without using additional apparatus; all the factors which vary with the electron-beam potential can then be derived from a single diffraction pattern of a standard substance. A graph has also been prepared to allow correction of errors in calculation due to large angles between the third-row axis and the electron beam. The improvement in accuracy due to the procedure is illustrated by results obtained using crystals of known unit-cells.

On the Single Crystal X-Ray Diffraction Pattern of Calcite

The method of analysis of double spectrometer rocking curves developed by L. P. Smith is reconsidered. Although from Smith's very general viewpoint, six experimental curves are needed for a complete analysis, it is shown that for rocking curves from calcite, taken with the usual type of double spectrometer, it should be possible to deduce the shape of the single crystal diffraction pattern from two rocking curves, the (1,+1) and (2,+2). A method of modifying the equations of the instrument to allow for a simple type of mosaic structure is indicated.The equations have been applied to rocking curves of Mo $K{\ensuremath{\alpha}}_{1}$ from calcite, supplied by L. G. Parratt. The method requires resolution of the observed curves into Fourier components, and a numerical method of doing this is described. The reliability of the components obtained can be tested by predicting the (1,-1) curve with them and comparing with experiment. In this way it is found that the curves are consistent as regards Fourier components of long period and large amplitude, but inconsistent in the short period, small amplitude components. A single crystal pattern is deduced, based mainly on the observed (1,-1) curve, with asymmetry as indicated by the (1,+1) and (2,+2) curves. It indicates that the crystals used do not have the flat-topped Darwin-Ewald-Prins diffraction pattern. Possible causes of the short period discrepancy have been investigated, but an adequate explanation has not been found.