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The diffraction properties of curved silicon crystals, with curvature radii between ∞ and 25 m obtained by microscopic techniques, were investigated by means of a neutron diffractometer. The ratio of neutron reflectivity between plane and curved silicon crystals was measured as a function of the neutron wavelength using different reflecting planes in both Bragg and Laue cases in symmetrical and asymmetrical conditions. The experimental results were interpreted with the results of theoretical investigations on the dynamical theory of diffraction applied to the curved-crystal case. The implications of this work on neutron monochromator design are briefly discussed.

Transmission electron diffraction studies of thin films of SiO and mixtures of SiO and B 2 O 3 vacuum evaporated onto air-cleaved NaCl crystals indicate that the amorphism of SiO films is increased by the addition of B 2 O 3 , and that the particle size is a minimum for 5% B 2 O 3 in the thickness range 500–1500 A.

Alloys of vanadium containing up to 10 at.% oxygen were examined by transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. The presence of the V 9 O phase was confirmed and several electron diffraction patterns of important reciprocal lattice planes of this phase were obtained. These patterns are explained using a long-period-superlattice which is 4 × 4 × 6 vanadium atom cells in dimension. It is further shown that the sites of this long-period-superlattice correspond to tetrahedral positions for the interstitial atoms. The possibility of octahedral site occupation is discussed.

SummaryThe positions of all the atoms including hydrogen have been found by a partial three-dimensional single-crystal neutron-diffraction study in which about one-third of the reflections in the reciprocal sphere to 1·5 Å were measured. The hydroxyl group is perpendicular to the plane of the silicate sheets. The fluorine content of this phlogopite is enough to occupy 25 % of the (OH, F) sites. Site occupancy refinement suggests that there is a small deficiency of hydrogen at the remaining sites and that the two crystallographically different octahedral sites are fully occupied by the same proportions of Mg, Ti, Fe, and Ca.

STEEDS et al. have published pictures showing effects of upperlayer interactions in molybdenite1,2. Because of its use in structure analysis it seems worthwhile to set down rules from the literature which relate electron diffraction symmetries to three-dimensional crystal symmetries. As distinct from problems which can be solved by considering only zero-layer interactions, such as the determination of a polar axis in the plane of projection3,4, the total crystal symmetry, including the boundaries, must be considered when upper-layer interactions are important. As a simple example some results obtained from a highly tilted crystal are given, and I also comment on the conclusions of Steeds et al.1,2.

Powder Cd of 99.999% purity was prepared at room temperature (25 °C) and x-ray diffraction patterns were obtained using CuKaα radiation with Ni-filter. The line broadening was analyzed after incorporating the appropriate correction factors. At room temperature Cd was found to have large particle size (653 A), small root mean square strain (.001), small deformation fault probability a (.003). and negligible growth fault probability β(0). Compared to other hep metals which have been studied earlier and which have higher melting temperatures, metal Cd is much less affected by mechanical deformation at room temperature.

This paper outlines the difficulty of resolving two overlapping symmetrical peaks of the same unknown shape as might be seen in x-ray or electron diffraction studies of epitaxial layers.

A manganese-bearing mineral characterized by a black hair-like surface crystal growth, and somewhat unique to the Socorro County, New Mexico Area, has been referred to as psilomelane or pseudo-pyrolusite. X-ray diffraction measurements indicated the structure to be the tetragonal (a=4.42 A, c=2.87A) MnO2 (pyrolusite) structure; with α-Mn enrichment. Detailed examinations of the mineral specimens made in the scanning and transmission electron microscopes showed the fiber crystals to be pseudo-fluted as a result of an apparent stacking of long needles to form continuous single-crystral bundles oriented along the x-axis These crystals were shown by selected-area electron diffraction to be composed of extended superstructure cells, and these to be commposed of as many as 10 MnO2 unit cells stacked along the x-axis; interrupted by a stacking fault shear of the basic MnO2 lattice resulting in stacking faults. Individual whisker crystals were observed to be terminated by crystallographic facets which is indicative of solution growth expected on considering their geological and mineralogical environment.

The reflection of an incident «low-energy» (10 eV≲E≲≲500 eV) electron by a solid is dominated by the consequences of its interactions with the valence electrons in the solid. In particular, the high probability that the incident electron suffers an inelastic electron-electron collision renders the elastic electron-solid scattering cross-sections direct measures of the electronic structure and positions of ion cores within 10 A or less of the solid’s surface. We indicate the major features of the coherent reflection,i.e. diffraction, of such low-energy electrons from planar surfaces of single-crystal solids and of current theoretical models of this phenomenon. Emphasis is placed on those features of the electron-electron and electron-ion-core interactions which permit the extraction of the atomic geometry of surface species from measured low-energy electron diffraction (LEED) intensities. Analysis of the elastic low-energy electron diffraction intensities from the low-index faces of aluminum reveals the relatively modest influence on these intensities of the detailed shape of the one-electron optical potential and of the electronic structure of the ion cores. This result, in turn, is used to analyse the atomic structure of Ni(100)-c(2×2)-S, Ni(100)-c(2×2)-O and Cu(100)-c(2×2)-O adsorbed overlayers. Finally, we indicate the present status of applications of LEED intensity analyses to determine the atomic geometry of periodic surface structures.

We have established by electron microscopy and electron diffraction the existence of several crystallographic shear phases in the family of chromium oxides CrnO2n−1, where n = 4 and 6. As in the systems TinO2n−1 and VnO2n−1, the phases are based on crystallographic shear on the planes {121}. A further series of phases found in this study show a superlattice along g 210 and bear similarities to the MmO2m−2 phases found by Gibb and Anderson in the Ga2O3TiO2 system.

An investigation by electron diffraction, transmission and scanning electron microscopy, and energy-dispersive X-ray analysis has shown that Ta additions to a 40-30-30 Co-Cr-Ni-base alloy strengthen by ordering and by formation of coherent α-Co3Ta precipitate. However, increasing Ta content increases the proportion of the hexagonal phase and decreases ductility.

Thin films of cobalt, prepared in ultra-high-vacuum at 4 K and examined in situ by scanning electron diffraction, are shown to be amorphous with a radial distribution function similar to that obtained theoretically by serial deposition of atoms in the computer-simulated model developed by Bennett. The effects of removal of lossy electrons (by velocity filtering), subtraction of substrate background, and multiple scattering on the diffraction profile are investigated and discussed.

Thermal neutron diffraction has been studied using single and double quartz crystal systems vibrating in the compressional and flexure modes. A spectral shift has been noted for a vibrating crystal resulting in an increase in most probably diffracted neutron wavelength from 2.2 A to 2.9 A. Double crystal diffraction was found to yield a 95% survival of once diffracted neutrons in the second diffraction, but with a large beam angular divergence. Large amplitude flexure mode studies produced a 30% reduction in diffracted intensity and no measurable effect on beam divergence.

Neutron diffraction topography with thermal neutrons has been used to observe the three-dimensional strain fields in a hot-pressed germanium crystal 8 mm thick. In the stereo-paired and section topographs the strain fields were found to be columnar along the press direction. This result was confirmed by X-ray diffraction topography performed on slices cut from the same crystal.

Electron microscope and electron diffraction studies on the surfaces of CP‐4 etched germanium specimens have shown that the changes in etching behavior induced by fast neutron irradiation occur as a result of a gross change in chemical behavior and cannot be due to local variations in the etching rate in the vicinity of the structural defects introduced by the irradiation. Observations on network structures which are produced under certain conditions of etching indicate that these arise as a result of mechanical preparation of the surfaces or from changes in the etching process and are apparently unrelated to any prior substructure in the material.

The temperature dependence of dynamically influenced electron diffraction intensities of a polycrystalline aluminum foil was measured in the temperature range 150–800°K. It is shown that the experimentally determined effective Debye Waller factors exp (-α g M g ) for these reflections (g) are in good agreement with theoretical calculations, based on the dynamical theory of electron diffraction.

A simple algebraic criterion based on reciprocal lattice geometry was established. It allows a straightforward construction of the distribution of intensity peaks on an electron diffraction pattern along layer lines associated with any crystallographic direction. It can be used to determine the fibre texture axis in materials composed of crystals of arbitrary symmetry. The method was applied to the determination of the fibre texture of thin films of PbO.

X-ray diffraction patterns of vitreous Si${\mathrm{O}}_{2}$ and Ge${\mathrm{O}}_{2}$ have been made in an evacuated camera using Cu $K\ensuremath{\alpha}$ radiation monochromatized by crystal reflection. Intensity curves are obtained from the microphotometer records in the usual way. A method is developed for calculating the scattering of x-rays in an amorphous solid and is applied to the diffraction patterns of glass. In vitreous Si${\mathrm{O}}_{2}$ each Si is tetrahedrally surrounded by 4 oxygens at a distance Si---O=1.60A, and each oxygen is shared between two such tetrahedral groups. The resulting network which is built up is a random network, it does not repeat at regular intervals, and is accordingly non-crystalline. From this picture of the glassy state, scattering curves are calculated for vitreous Si${\mathrm{O}}_{2}$ and Ge${\mathrm{O}}_{2}$ which are in good agreement with the experimental curves.

The molecular structure of meta-difluorobenzene in the gas phase has been determined by electron diffraction at room temperature. The carbon ring deviates slightly from D6h symmetry. The four C-C distances adjacent to the F atoms are 1.384 A, the two other C-C distances are slightly longer, i.e. 1.405 A. The C-F and C-H distances are 1.324 and 1.107 A. The C-C-F valency angle is 119.5°.

An apparatus is described for the class‐room demonstration of electron diffraction photographs obtained from thin metallic films and using the range 2000 to 15000 volts. It is very simple to build and reasonably stable. The method of operation is explained.

The nature of exchange reflexions in low-energy electron diffraction from antiferromagnetic nickel oxide was studied in particular reference to its dependence on the diffraction condition of electrons, which was, in the present study, changed primarily by rotating the crystal at a fixed electron energy. It was pointed out that the exchange reflexions are subject to the three-dimensional diffraction conditions appropriate to the reciprocal lattice points which correspond to the magnetic structure, and also that the intensities of these weak reflexions may be favourably enhanced by the dynamical diffraction effect under the condition which involves the simultaneous presence of a strong regular reflexion.

SummaryA time saving method has been applied for the determination of retained austenite.The method involved is based on the approach of energy dispersive X-ray diffraction analysis. With this approach, polychromatic radiation from the X-ray tube is used and diffraction maxima will occur at a fixed angle 2θ in as many wavelengths or energies as “d“ values are present.Giessen and Gordon published the first application of this method to powder diffraction analysis in 1968 for the identification of crystal structures. As the determination of retained austenite is a quantitative type of analysis, based upon identification of the crystal structure, the new approach should also be applicable in principle.With almost 100 samples of unknown austenite content, experiments have been carried out both with the conventional and the energy dispersive X-ray diffraction technique. The results obtained are closely comparable and the retained austenite values together with the errors are shown.For these measurements, experiments have been carried out with the energy dispersive technique to determine the relation between the known concentration of retained austenite in a number of standards and the intensity correction factors (R). The results obtained from these experiments have shown good reproducibility of the intensity correction factors.Using this technique, a five-fold reduction in analysis time is possible over the conventional technique with no reduction in accuracy.

A universal electron diffraction microscope, as we call it, consists of three stage electron lens and two specimen chambers and functions both as an electron microscope and as an electron diffraction unit. This instrument can be used in the following seven ways:(1) Electron microscope; range of magnification between 800 and 20 000 times can be covered continuously.(2) Electron microdiffraction unit; electron diffraction pattern characteristic of any small area of a specimen under microscopic observation can be revealed by a switch.(3) Dark‐field electron microscopic image.(4) High‐resolution electron diffraction unit.(5) Effective camera length of electron diffraction is variable from 0 to 250 cm.(6) Shadow micrographs of the specimen used in (4) can be directly obtained.(7) Shadow microdiffraction (probe diffraction); dark‐field microscopic image appears in each diffraction spot.The specimen in the second chamber can be heated at any temperature up to about 800°C and on which two kinds of substances can ...

The occurrence of diffuse bands in electron diffraction and their apparent non-appearance in x-ray diffraction is accounted for by differences in wave-length, intensity, crystal size, etc. Under suitable conditions it is expected that they may be observed with x rays. A qualitative comparison is made of the Fax?n-Waller theory, used to explain extra spots in the x-ray diffraction pattern, with the hypothesis advanced to account for the presence of diffuse bands. The former is in many respects equivalent to assuming approximate coherence in thermal vibrations over very limited regions of the crystal. If these regions shrink to unit-cell dimensions, the molecules therein vibrate very nearly independently, giving rise to diffuse bands, in addition to the usual Laue or Bragg spot patterns.

In the present work film morphology was studied by an electron diffraction method. The electron microscopy replica method seems to be insufficient to give unambiguous information concerning film morphology and the growth process, but a combination of diffraction data and electron microscope observations gives much more complete information. We applied these methods to investigations of Ge epitaxial films on GaAs and Si substrates at different stages of growth (at thicknesses of 20 A upwards).

Calculations based on n-beam dynamical diffraction theory have shown that the intensities of rings and arcs in diffraction patterns from polycrystalline materials are strongly dependent on the experimental conditions. For arc patterns from BiOCl, calculations confirm a revised formula for the intensities from very thin crystals and indicate dependences on the distributions of orientation, thickness and bending of the crystals which are sufficient to account for the wide deviations of recent experimental results from the predictions of the primary extinction formula, based on the two-beam approximation. Inferences regarding the possible errors in electron diffraction analysis of crystal structures, especially for materials containing heavy atoms, are drawn from calculations relating to the intensities of arc patterns from AgTISe2. It is suggested that n-beam calculations should be made in order to avoid serious error in the refinement stages of a structure analysis.

Electron microscopic observations of the first suboxide phase formed in the Vanadium-Oxygen system are given. The VO x suboxide (VO 0.06 –VO 0.1 ) is found by means of electron diffraction to be tetragonal ( c a =0.97−0.96 ), the X-ray data being consistent with this result. The twinned structure of this phase and the direct resolution of a long period superstructure are presented.