Showing papers on "Electron backscatter diffraction published in 1979"

Convergent Beam Electron Diffraction

Abstract: Convergent beam electron diffraction (CBD) is a technique with a long history of gradual development which has recently become widely available through the development of commercial TEM/STEM electron microscopes. The technique was discovered by KOSSELL and MOLLENSTEDT (1939) who obtained some quite remarkably good results when one realizes that the size of focussed probe they were working with was comparatively large. Most specimens are so irregular that there would be considerably thickness variation within such areas producing a thickness average of the information. Further, few specimens are so flat that some important angular average will not occur over such areas. Thickness and orientation are two crucial parameters of electron diffraction and it is essential to eliminate their variation within the illuminated volume if meaningful results are to be obtained.

Neutron diffraction from clay-water systems

Abstract: The use of neutron diffraction to determine some of the structural properties of montmorillonite-water systems at low water concentrations is described. The samples were prepared by compression or suction to give clay samples with between one and three molecular layers of water between the plates. About 10% of the platelets in the clay are randomly oriented. The remainder are partially oriented in the plane of the sample, with an angular spread of 40° about the mean orientation. It is suggested that these oriented domains are formed from the larger platelets present in the system. The Bragg diffraction pattern is better explained by a disordered lattice model rather than by a mixture model with small particles having a well-defined lattice spacing. We have fitted both the intensities of (00l) reflections and the shape of the (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value. The half width of the spread is about 10% of the lattice spacing. No significant structural differences are found between Li, Na, K, and Cs montmorillonites. The method of preparation has no effect on the structural properties of the large platelet particles but does affect the randomly oriented fraction. The lattice spacing of the latter appears to be better defined for samples prepared by compression. Experiments on the variation of lattice spacing with humidity indicate that the structural model we have used is adequate except at humidities where the system is changing over from one to two, or two to three water layers.

Nucleation of recrystallization in compressed aluminium: studies by electron microscopy and Kikuchi diffraction

Abstract: Following the earlier investigation of recrystallization of aluminium by Bellier and Doherty [1] by transmission Kossel diffraction, the details of the nucleation process were studied by transmission electron microscopy and Kikuchi electron diffraction. This showed that nucleation appeared to occur via a sub-grain coalescence process that occurred selectively at deformation bands and at deformation band, grain boundary junctions. Nucleation occurred only at grain boundaries and at deformation bands. The condition for continued growth, of enlarged sub-grains of length 2L, along the grain boundary L>2r(γs/γg) where γs is the sub-boundary energy and γg the grain-boundary energy, was found to be obeyed. The values of the stored energy calculated from the measured sub-grain sizes and misorientations were less than the reported experimental value, indicating that in as-deformed aluminium the dislocation arrays in the sub-boundaries may not have the lowest energy structure assumed in the calculation.

Elements of X-ray diffraction

Abstract: Intended to acquaint the reader with the theory of x-ray diffraction, the experimental methods involved, and the main applications. The book is a collection of principles and methods stressing X-ray diffraction rather than metallurgy. The book is written entirely in terms of the Bragg law and can be read without any knowledge of the reciprocal lattice. It is divided into three main parts— Fundamentals; experimental methods; and applications. Designed for beginners, not as a reference tool for the advanced reader.

Direct phasing of electron diffraction data from organic crystals: the effect ofn-beam dynamical scattering

Abstract: The conditions under which direct phasing methods might be used to determine the crystallographic phases from electron diffraction intensity data are investigated through numerical calculations for two organic crystals. The Cowley-Moodie multislice formulation of dynamical diffraction theory is used to calculate the diffraction intensity data for various crystal thicknesses, at electron energies of 100 keV and 1.0 MeV. The direct phasing method is found to give generally correct phases up to a crystal thickness of about 75 A at 100 keV. The use of higher electron energy (i.e. 1.0 MeV) produces a significant improvement in the success of the direct phasing approach at crystal thicknesses greater than 75 A.

Diffraction effects and images from inclined grain boundaries in polycrystalline thin foils

Abstract: The geometry of the reciprocal lattice associated with the periodic structure of inclined grain boundaries in thin foils is described. Electron diffraction effects consistent with the reciprocal lattice were observed from inclined boundaries. It is pointed out that, before any extra diffraction effects can be attributed to a periodic grain boundary structure, it is necessary to check for the possible contributions of double diffraction. Techniques for performing these checks were developed and applied to several boundaries observed in this study. The influence of grain boundary as well as spurious diffraction effects on the image of the boundary is described. Examples are discussed where the relationship between the image end the diffraction pattern is not straightforward. For boundaries containing relatively short-period structures, both the inclination of the boundary plane and the periodicity of the structure can be determined using diffraction techniques with little if any information require...

An electron diffraction study of amorphous silicon oxide films

Abstract: Amorphous silicon oxide films have been examined by high energy electron diffraction using the sector-microphotometer method of data collection common to gas phase electron diffraction. This data was analyzed with a least-squares procedure that is designed to minimize extraneous detail in the radial distribution function obtained by the Fourier sine transform of the interference function. The results of this analysis for thin film SiO 2 show that the overall bonding topology of the thin film agress well with that of bulk (vitreous) SiO 2 examined by X-ray diffraction. The experimental short distance parameters for the films whose composition was determined to be ∼SiO 1.3 , SiO, and SiO 0.8 are found to be consistent with those expected for a mixture of tetrahedrally bonded amorphous Si and SiO 2 phases in which the scale of the Si-like and SiO 2 -like regions is of the order of a few basic tetrahedral units. This result is in agreement with previous examinations of SiO powder by X-rays and a previous examination of thin silicon oxide films by electron diffraction.

Amorphous Ribbons of LiNbO3, PbTiO3 and (PbTiO3)0.9(B2O3)0.1

Abstract: Amorphous ribbons of LiNbO3, PbTiO3, and (PbTiO3)0.9(B2O3)0.1 were obtained by a roller quenching technique. These ribbons were examined by electron diffraction as well as by X-ray diffraction experiments, and were proved to be in the amorphous state. Their dielectric constant increased rapidly with increase of temperature.

A search–match system for X-ray powder diffraction data

Abstract: A computer program which can identify the crystalline component phases of a mixture from its X-ray diffraction pattern is described. The program uses the data base of powder diffraction patterns maintained by the Joint Committee on Powder Diffraction Standards. The `reverse searching' technique employed permits the identification of each component and provides an estimate of confidence in the identification. Errors in measured spacings and intensities are tolerated by the program. The interactive search-match system is available for general use via a networked timeshared computer.

Non‐destructive investigation of texture by neutron diffraction

Abstract: Texture measurement as a function of depth with a collimated thermal neutron beam is demonstrated for a `two-layer plate' geometry sample with preliminary results for a copper cone.

Scanning microdiffraction of polymers.

Abstract: Scanning transmission electron microscopy (STEM) has been suggested to have advantages over conventional transmission electron microscopy (CTEM) for the observation of diffraction contrast features and diffraction patterns from radiation-sensitive crystalline polymers. For many applications it is desirable to obtain successive diffraction patterns from very small adjacent areas. Several microarea diffraction techniques are available using CTEM and STEM. The most useful technique is scanning microarea diffraction used in conjunction with STEM dark-field imaging. Using this technique we have obtained diffraction patterns from regions as small as 100 nm×100 nm for a 12 nm thick polyethylene single crystal. Adjacent microarea diffraction patterns can be obtained while only radiation-damaging the diffracting region. This allows mapping of the specimen crystallography on a very fine scale as well as allowing one to obtain a diffraction pattern for selecting various STEM dark-field conditions while only damaging a small portion of the specimen before the dark-field image is recorded.