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Showing papers on "Electron backscatter diffraction published in 1989"


BookDOI
01 Jan 1989
TL;DR: The main topics of the workshop, Reflection High Energy Electron Diffraction (RHEED) and Reflection Electron Microscopy (REM), have a common basis in the diffraction processes which high energy electrons undergo when they interact with solid surfaces at grazing angles as discussed by the authors.
Abstract: This volume contains the papers presented at the NATO Advanced Research Workshop in "Reflection High Energy Electron Diffraction and Reflection Electron Imaging of Surfaces" held at the Koningshof conference center, Veldhoven, the Netherlands, June 15-19, 1987. The main topics of the workshop, Reflection High Energy Electron Diffraction (RHEED) and Reflection Electron Microscopy (REM), have a common basis in the diffraction processes which high energy electrons undergo when they interact with solid surfaces at grazing angles. However, while REM is a new technique developed on the basis of recent advances in transmission electron microscopy, RHEED is an old method in surface crystallography going back to the discovery of electron diffraction in 1927 by Davisson and Germer. Until the development of ultra high vacuum techniques in the 1960's made instruments using slow electrons more accessable, RHEED was the dominating electron diffraction technique. Since then and until recently the method of Low Energy Electron Diffraction (LEED) largely surpassed RHEED in popularity in surface studies. The two methods are closely related of course, each with its own specific advantages. The grazing angle geometry of RHEED has now become a very useful feature because this makes it ideally suited for combination with the thin growth technique of Molecular Beam Epitaxy (MBE). This combination allows in-situ studies of freshly grown and even growing surfaces, opening up new areas of research of both fundamental and technological importance.

279 citations



Journal ArticleDOI
01 Jan 1989-Nature
TL;DR: In this paper, a new copper oxide superconductor with an onset tem-perature of 28 K was found in the Nd-Ce-Sr-Cu-O system.
Abstract: Recently, a new copper oxide superconductor with an onset tem-perature of 28 K was found in the Nd–Ce–Sr–Cu–O system1. The superconducting phase was identified by X-ray diffraction and electron microscopy2, and the metal-atom positions are identical with those in the K2NiF4 or Nd2CuO4 structure3, except for the order of the cations Nd(Ce) and Sr. Here we report the refinement of the crystal structure using neutron powder diffraction. We find that it comprises alternating slabs of the K2NiF4 and Nd2CuO4 structures, and that all the copper atoms are crystallographically identical, with oxygen in fivefold (square-pyramidal) coordination. In having only one kind of copper site, this new compound is structurally simpler than the other CuO5-bearing superconductors such as YBa2Cu3O7, and may therefore be particularly helpful in the effort to understand the origins of high-temperature superconductivity.

138 citations


Journal ArticleDOI
TL;DR: In this paper, a model for the superstructure of Bi 2 Sr 2 CaCu 2 O 8.2 was proposed, which involves the addition of one in ten oxygen atoms in the BiO planes and a displacement of the surrounding atoms.
Abstract: A model is proposed for the superstructure of Bi 2 Sr 2 CaCu 2 O 8.2 . It involves the addition of one in ten oxygen atoms in the BiO planes and a displacement of the surrounding atoms. This model is consistent with electron microscope, neutron and X-ray diffraction data. In particular it is consistent with the symmetry determined by convergent beam electron diffraction and with details of the high resolution electron microscope image contrast.

72 citations


Journal ArticleDOI
TL;DR: In this paper, a low temperature molten salt electrochemical technique has been used for the preparation of Ba6K4BiO3 and the resulting crystalline material has been characterized by X-Ray diffraction, scanning electron microscopy and by energy dispersive X-ray analysis.

70 citations


Journal ArticleDOI
TL;DR: In this article, the symmetry determination of three-dimensional (usual) crystals, four-dimensional and one-dimensionally incommensurate (quasicrystals) by convergent-beam electron diffraction is described and demonstrated using real materials.
Abstract: Symmetry determination of three-dimensional (usual) crystals, four-dimensional (one-dimensionally incommensurate) crystals and five- and six-dimensional crystals (quasicrystals) by convergent-beam electron diffraction is described and demonstrated using real materials. Crystal structure refinement based on the dynamical theory of electron diffraction is described for the low-temperture phase of SrTiO3.

45 citations


Journal ArticleDOI
TL;DR: In this article, the advantages of neutron diffraction texture analysis are compared to those of X-ray texture analysis, due to the lower absorption coefficient and the ability to measure magnetic textures.
Abstract: Neutron diffraction texture analysis is based on pole figure measurement followed by pole figure inversion. Neutron diffraction pole figure measurement is quite similar to that by X-rays. There are, however, several advantages in detail which are mainly due to the lower absorption coefficient. Besides these quantitative differences, there is one principle difference between the two methods. Neutron diffraction allows the magnetic texture to be measured which is not possible by X-rays. The paper gives a survey on the advantages of neutron diffraction texture analysis which are only counteracted by the limited availability and higher costs of neutron diffraction.

37 citations


Journal ArticleDOI
TL;DR: In this paper, a low-energy electron diffraction (LEED) crystallographic analysis has been undertaken to assess the lateral and vertical relaxations for the Cu(100)-(2\ifmmode\times\else\texttimes\fi{}2)-S surface structure.
Abstract: A low-energy electron diffraction (LEED) crystallographic analysis has been undertaken to assess the lateral and vertical relaxations for the Cu(100)-(2\ifmmode\times\else\texttimes\fi{}2)-S surface structure. The motivation was provided by the recent report with angle-resolved photoemission extended fine structure (ARPEFS) by Bahr et al. [Phys. Rev. B 35, 3773 (1987)]. It was found that the surface structure given by ARPEFS does not account well for the measured LEED intensity curves, although these curves can be reasonably accommodated by a structural model with components of relaxation in some opposite senses to those previously reported.

33 citations


Journal ArticleDOI
TL;DR: In this paper, electron diffraction was used to study the order and phase transition of cadmium arachidate monolayers and multilayers and found that the loss of intensity on heating is reversible for both the monolayer and the multilayer up to temperatures where the peaks fully disappear.

33 citations


Journal ArticleDOI
TL;DR: In this article, a dynamical and kinematical model of x-ray scatting on multilayers is presented, where the dynamical model gives only a rigotions description of the X-ray scattering.
Abstract: X-ray diffraction patterns from layered structures yield detailed information on their structural parameters such as strain profile, chemical composition, layer thickness and interface quality. Any variation of the period, thickness of the individual layers, composition and homogeneity of the supelattics can be also determined. For an accurate determination of the structural properties a theoretical modeling of the experimental diffraction patters is, however, requird. The appropriate dynamical and kinematical models of x-ray scatting on multilayers are here reviewed and compared: The dynamical model gives only a rigotions description of the x-ray scattering. The unique capability of the x-ray diffraction technique to analyze multilayer structures is illustrated by investigations of the AlxGa1-xAs/GaAs and GaxIn1-xAs/AlyIn1-y As material systems. X-ray scattering on periodic, quasiperiodic (Fibonacci superlattics), automatic (Theu-Morse superlattics), as well as on random systems is discussed.

30 citations


Journal ArticleDOI
TL;DR: In this paper, K{sub 1.35}Ti{sub 8}O{sub 16} is obtained in the form of dark blue tetragonal crystals of the space group I4/m having the hollandite structure with a = 1.018.



Journal ArticleDOI
01 May 1989-Polymer
TL;DR: In this article, the crystal structure of polypivalolactone (γ-PPVL) was determined from electron diffraction data and tested with the Rietveld method against X-ray powder diffraction profiles.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the circular arcs and high-order Laue zone (HOLZ) fine lines observed in both Kikuchi-line and convergent-beam electron diffraction (CBED) patterns have been shown to be consistent with the concept of Bloch-wave channeling of fast electrons along rows of atoms.
Abstract: The circular arcs and high-order Laue zone (HOLZ) fine lines observed in both Kikuchi-line and convergent-beam electron diffraction (CBED) patterns have been shown to be consistent with the concept of Bloch-wave channeling of fast electrons along rows of atoms. This interpretation has the advantages that it provides a direct correlation between HOLZ lines and the crystal periodicity along the incident-beam direction, and forms a basis which could be incorporated into a more rigorous electron diffraction theory in the future for understanding the extreme Laue and Bragg cases of electron diffraction, as well as the intermediate reflection and transmission high-energy electron diffraction (RTHEED). Examples are given of all three types of CBED, RHEED and RTHEED patterns from Pt and GaAs single crystals, which show the common dynamical diffraction effects, circular arcs and HOLZ fine lines, resulting from Bloch-wave channeling.

Journal ArticleDOI
TL;DR: Examples of the use of CBED techniques in measuring lattice parameters and strain are given from studies of precipitation (including misfit measurements) and from investigations of partially recrystallised microstructures to illustrate the advantages and limitations of the CBED technique.
Abstract: A brief review is presented of the methods of measuring lattice parameters and strain using diffraction techniques. The presence of strain leads to broadening of diffraction maxima, which is normally separable from any broadening caused by size. The special advantages of the convergent beam electron diffraction (CBED) technique is the local nature from which the data are derived. Examples of the use of CBED techniques in measuring lattice parameters and strain are given from studies of precipitation (including misfit measurements) and from investigations of partially recrystallised microstructures. These examples are used to illustrate the advantages and limitations of the CBED technique.

Journal ArticleDOI
TL;DR: In this paper, the diffraction of fast electrons from crystals in the reflection geometry (RHEED) is in many respects similar to low energy electron diffraction (LEED), because the components of the wave vectors normal to the surface are of the same order of magnitude due to the grazing incidence of the electron beam and its higher energy.

Journal ArticleDOI
R. Vincent1
TL;DR: The techniques required to record standard convergent beam electron diffraction patterns in an analytical electron microscope are discussed in detail, with emphasis on the design of electron optics in commercial instruments.
Abstract: The techniques required to record standard convergent beam electron diffraction patterns in an analytical electron microscope are discussed in detail, with emphasis on the design of electron optics in commercial instruments. Practical comments are included on specimen preparation, the influence of crystal defects, tilting to major zone axes, and alignment of the instrument. The influence of parameters under experimental control such as probe size, accelerating voltage, temperature, specimen thickness, and convergence angle is discussed in detail. Some comments are included on the alignment and limitations of large angle patterns formed by a defocused probe.


Journal ArticleDOI
TL;DR: In this article, the crystallographic structure of small Pd particles formed during the earliest stages of vapor deposition onto refractory oxide supports was studied by energy filtered in situ UHV scanning transmission electron diffraction (STED).
Abstract: The crystallographic structure of small Pd particles formed during the earliest stages of vapor deposition onto refractory oxide supports was studied by energy filtered in situ UHV scanning transmission electron diffraction (STED). Although only the average structure of particles can be obtained by this high‐precision, large area diffraction technique, its main advantage over high‐resolution transmission electron microscopy (TEM) is the drastic reduction of radiation damage effects. On‐line processed experimental diffraction data were compared to calculated elastic diffraction intensities and radial distribution functions obtained by Fourier transformation. The results show conclusive evidence that small Pd clusters of less than about 2 nm size prefer non‐fcc icosahedral packaging over the standard fcc structure, which confirms earlier theoretical predictions for minimum energy cluster configurations. Standard fcc structures always dominate in later stages of growth with increasing particle size.

Journal ArticleDOI
TL;DR: In this paper, the pole figure determination by means of TOF technique is considered and the main parameters of the Dubna texture facility are given, and further developments of the experimental technique are considered.
Abstract: For the majority of isotopes the thermal neutron absorption cross section is two or more orders lower than that for X-rays. This makes neutron diffraction well-suited for bulk texture investigations. Some characteristics of neutron diffraction are discussed. The principles of neutron time-of-flight diffraction are described. The pole figure determination by means of TOF technique is considered. The main parameters of the present Dubna texture facility are given. Further developments of the experimental technique are considered. The application of the TOF technique for inverse pole figure measurement is discussed as an approach to direct observation of the texture forming process. The magnetic moments of neutrons can be used to study magnetic textures. Two different techniques are discussed.


Journal ArticleDOI
TL;DR: Neutron diffraction methods for texture analysis are closely parallel to well-known X-ray diffraction techniques as discussed by the authors, however, the effect of anisotropic absorption in multi-phase materials can be neglected in most cases.
Abstract: Neutron diffraction methods for texture analysis are closely parallel to well-known X-ray diffraction techniques. The chief advantage of neutron diffraction over X-ray diffraction, however, arises from the fact that the interaction of neutrons with matter is relatively weak, and consequently the penetration depth of neutrons is 102–103 times larger than that of X-rays. Hence neutron diffraction is an efficient tool for measuring textures in multi-phase systems. Based on the high transmission of a neutron beam the effect of anisotropic absorption in multi-phase materials can be neglected in most cases. Moreover, the analysis of bulk textures becomes possible, such that textures in a wide variety of multi-phase systems can be studied which are of special interest in engineering and science (metals, alloys, composites, ceramics and geological specimens).

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional spherical mirror analyzer was used to find circular diffraction patterns from a bulk crystal in RHEED patterns near superstructural spots from a surface structure.


Journal ArticleDOI
TL;DR: In this article, the crystal structure of (Zn 1− x Mn x ) 3 As 2 has been determined with neutron powder diffraction for x = 0, 0.08 and 0.135.
Abstract: The crystal structure of (Zn 1− x Mn x ) 3 As 2 has been determined with neutron powder diffraction for x = 0, 0.08 and 0.135. The structure of these compounds turned out to be the same as that of the α-phase of Cd 3 As 2 , space group I4 1 cd. The diffraction for a sample with nominal x = 0.2 indicates the presence of several phases.

Journal ArticleDOI
TL;DR: Gas-phase electron diffraction is one of the principal tools for the determination of accurate molecular geometry and has been used extensively in the literature to study structural changes in series of compounds or even during some chemical happenings.
Abstract: Gas-phase electron diffraction is one of the principal tools for the determination of accurate molecular geometry. Re- cently, research efforts have focused on the determination of structural changes in series of compounds or even during some chemical happenings rather than on the study of individual struc- tures. Internal rotation, substituent effects, the transition from vapor to crystal phase, and the formation of new bonds are among the chemical changes whose structural consequences are being examined. The study of unstable molecules and reaction products is facilitated by combined electron diffraction/quadrupole mass spectrometric experiments.

Journal ArticleDOI
TL;DR: The applications of electron diffraction and diffraction contrast electron microscopy with which to study the structure and dynamics of organic thin films are discussed and methods to reduce radiation damage and environmental protection of the thin film specimen are outlined.
Abstract: The applications of electron diffraction and diffraction contrast electron microscopy with which to study the structure and dynamics of organic thin films are discussed. The techniques of making thin film deposits on substrates and of forming free-standing thin films over holes on the substrate are described. Selected area electron diffraction and diffraction contrast imaging techniques for thin film studies are elaborated, and examples are given. Methods to reduce radiation damage and environmental protection of the thin film specimen are outlined. The interpretation of electron diffraction and imaging data is given for three cases: (1) The effects of film tilting and molecular tilting (with respect to the film plane) are examined. (2) The detection of phase transition is illustrated. (3) The use of labels to mark film domains is shown together with the measurement of dynamic movement.