Diffraction effects from interfaces

1987 ◽  
Vol 45 ◽  
pp. 38-41
Author(s):  
J. M. Vitek
Keyword(s):  
Grain Boundaries ◽  
Theoretical Work ◽  
Real Space ◽  
Periodic Array ◽  
Interface Plane ◽  
Fine Scale ◽  
Structural Distortions ◽  
New Information ◽  
Electron Microscopes ◽  
Diffraction Effects

The ability of electron microscopes to examine the structure and composition of materials on a very fine scale has paved the way for a renewed interest in examining the structure at interfaces and grain boundaries. Complemented by theoretical work on the structure of interfaces, much new information has become available. Among the various techniques available for studying the structure at interfaces, diffraction experiments have proved to be very useful. It has been shown, for example, that a periodic array of defects exists within the plane of the interface, leading to extra reflections in the plane of the interface. More recently, the diffraction behavior in the direction perpendicular to the interface plane has been examined. By considering diffraction effects in this direction only (to be referred to as the z direction in real space and the L direction in reciprocal space), information can be derived on the structural distortions in this direction near the interface without interference from any arrays of defects within the interface plane.

Determination of the lattice translation across {110} APBs in GaAs

1988 ◽  
Vol 46 ◽  
pp. 600-601
Author(s):  
D.R. Rasmussen ◽  
N.-H. Cho ◽  
C.B. Carter
Keyword(s):  
Grain Boundaries ◽  
Lower Energy ◽  
Antiphase Boundary ◽  
The Other ◽  
Boundary Structure ◽  
Interface Plane ◽  
Inversion Symmetry ◽  
High Angle ◽  
Equilibrium Distance

Domains in GaAs can exist which are related to one another by the inversion symmetry, i.e., the sites of gallium and arsenic in one domain are interchanged in the other domain. The boundary between these two different domains is known as an antiphase boundary [1], In the terminology used to describe grain boundaries, the grains on either side of this boundary can be regarded as being Σ=1-related. For the {110} interface plane, in particular, there are equal numbers of GaGa and As-As anti-site bonds across the interface. The equilibrium distance between two atoms of the same kind crossing the boundary is expected to be different from the length of normal GaAs bonds in the bulk. Therefore, the relative position of each grain on either side of an APB may be translated such that the boundary can have a lower energy situation. This translation does not affect the perfect Σ=1 coincidence site relationship. Such a lattice translation is expected for all high-angle grain boundaries as a way of relaxation of the boundary structure.

Diffraction effects from inclined grain boundaries in polycrystalline thin foils

1978 ◽  
Vol 36 (1) ◽  
pp. 420-421
Author(s):  
C.B. Carter ◽  
A.M. Donald ◽  
S.L. Sass
Keyword(s):  
Thin Film ◽  
Grain Boundaries ◽  
Boundary Plane ◽  
Foil Surface ◽  
Thin Foils ◽  
The Matrix ◽  
Firm Basis ◽  
Diffraction Patterns ◽  
Wave Matching ◽  
Diffraction Effects

Using thin-film gold bicrystals with the boundary plane parallel to the foil surface, it has been shown(l,2) that networks of grain boundary dislocations can act as diffraction gratings and give rise to subsidiary reflections close to the matrix reflections in electron diffraction patterns. Recently several groups of workers(3-5) have shown that inclined boundaries in polycrystalline specimens also produce extra reflections which may be due to the periodic nature of the boundaries. In general grain boundaries in polycrystalline specimens will be steeply inclined to the foil surface and additional reflections due to wave matching at the boundary(6) will also be present. The diffraction technique has the potential for providing detailed information on the structure of inclined boundaries (see, for example (5)), especially for the case where the image contains no useful information. In order to provide a firm basis for this technique, the geometry of the diffraction effects expected from inclined boundaries and the influence of these effects on the appearance of images will be examined.

Quantitative structure determination of interfaces through Z-contrast imaging and electron energy loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 104-105
Author(s):  
S. J. Pennycook ◽  
P. D. Nellist ◽  
N. D. Browning ◽  
P. A. Langjahr ◽  
M. Rühle
Keyword(s):  
Grain Boundaries ◽  
Cuprate Superconductors ◽  
Structure Refinement ◽  
3D Structure ◽  
Real Space ◽  
Contrast Imaging ◽  
Coordination Polyhedra ◽  
Burgers Vector ◽  
Z Contrast ◽  
Contrast Image

The simultaneous use of Z-contrast imaging with parallel detection EELS in the STEM provides a powerful means for determining the atomic structure of grain boundaries. The incoherent Z-contrast image of the high atomic number columns can be directly inverted to their real space arrangement, without the use of preconceived structure models. Positions and intensities may be accurately quantified through a maximum entropy analysis. Light elements that are not visible in the Z-contrast image can be studied through EELS; their coordination polyhedra determined from the spectral fine structure. It even appears feasible to contemplate 3D structure refinement through multiple scattering calculations.The power of this approach is illustrated by the recent study of a series of SrTiC>3 bicrystals, which has provided significant insight into some of the basic issues of grain boundaries in ceramics. Figure 1 shows the structural units deduced from a set of 24°, 36° and 65° symmetric boundaries, and 24° and 45° asymmetric boundaries. It can be seen that apart from unit cells and fragments from the perfect crystal, only three units are needed to construct any arbitrary tilt boundary. For symmetric boundaries, only two units are required, each having the same Burgers, vector of a<100>. Both units are pentagons, on either the Sr or Ti sublattice, and both contain two columns of the other sublattice, imaging in positions too close for the atoms in each column to be coplanar. Each column was therefore assumed to be half full, with the pair forming a single zig-zag column. For asymmetric boundaries, crystal geometry requires two types of dislocations; the additional unit was found to have a Burgers’ vector of a<110>. Such a unit is a larger source of strain, and is especially important to the transport characteristics of cuprate superconductors. These zig-zag columns avoid the problem of like-ion repulsion; they have also been seen in TiO2 and YBa2Cu3O7-x and may be a general feature of ionic materials.

Reconstruction and electronic properties of β-Li3PS4 |Li2S interface

2021 ◽  
Author(s):  
Chengdong Wei ◽  
Hongtao Xue ◽  
Zhou Li ◽  
Fenning Zhao ◽  
Fuling Tang
Keyword(s):  
Space Charge ◽  
Solid Electrolyte ◽  
Lattice Structure ◽  
Real Space ◽  
Space Charge Layer ◽  
Interface Plane ◽  
Charge Layer ◽  
Charge Density Difference ◽  
Interface Charge ◽  
Interface Contact

Abstract The morphology and properties of the interface between solid electrolyte and electrode have important impacts on all-solid-state lithium-sulfur batteries’ performance. We used the first-principles calculations to explore the interface between Li2S cathode and β-Li3PS4 (lithium thiophosphate, LPS) solid electrolyte, including lattice structure, mechanical, electrical properties, interface contact type, and charge distribution in real space. It is found that the interface is significantly reconstructed, and the Li atoms at the interface move mainly parallel to the interface plane. The interface density states introduce metallic properties, mainly contributed by the Li-s and S-s, -p orbitals in Li2S and S-p orbitals in LPS. The highest occupied molecular orbitals of the LPS electrolyte are lower than the electrochemical potential (Fermi level) of the Li2S cathode, thus the electrolyte and cathode materials are reasonable and stable in thermodynamics. Interface density of states shows electrons on the interface do not penetrate from Li2S into LPS, and do not leak electrons to cause electron conduct in LPS. Besides, the interface is an n-type Schottky barrier with a barrier value of 1.0 eV. The work-function of the interface indicates that there is a space charge layer by the redistribution of electrons, which is in agreement with the result of interface charge density difference. The electron/hole pairs will be separate, realizing high current charge and discharge capability because of the space charge layer.

Characterization of Grain Boundaries and Interfaces by High Resolution Transmission Electron Microscopy

1989 ◽  
Vol 153 ◽  
Author(s):  
William Krakow
Keyword(s):  
High Resolution ◽  
Grain Boundaries ◽  
Ohmic Contacts ◽  
Dielectric Material ◽  
Medium Voltage ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Interfacial Structures ◽  
Tilt Boundaries ◽  
Electron Microscopes

AbstractSeveral examples will be given of high resolution electron microscope images of both grain boundaries and interfaces and the methods which have been applied to understanding their atomic structure. Specific expitaxial interfacial structures considered are: Pd2Si/Si used for ohmic contacts, Al on Si overlayers and CaF2/Si where the CaF2, is an attractive possibility as a dielectric material. For the case of grain boundaries specific examples of both twist and tilt boundaries in Au will be given to show the imaging capability with the new generation of medium voltage electron microscopes.

The specific identity of the algal symbiont in Convoluta roscoffensis

1967 ◽  
Vol 47 (2) ◽  
pp. 445-464 ◽  
Author(s):  
Mary Parke ◽  
Irene Manton
Keyword(s):  
Water Samples ◽  
Distinct Species ◽  
Free Living ◽  
Algal Symbiont ◽  
New Information ◽  
Golgi System ◽  
Electron Microscopes ◽  
Convoluta Roscoffensis ◽  
Specific Identity

The algal symbiont of Convoluta roscoffensis (Graff) has been studied with the light and electron microscopes both in situ in worms collected from four localities on the coast of Brittany and in various forms of isolates in culture. The same organism has also been obtained from populations of free-living monads collected from sand and water samples adjacent to the Convoluta colonies. Its structure and behaviour in culture are described and illustrated. Platymonas convolutae sp.nov. is a very distinct species with a rough-surfaced theca and a pyrenoid with some new characters not previously recorded in other members of the group. Some new information on scale and theca production from the Golgi system has also been obtained.

Platymonas Impellucida Sp.Nov. From Puerto Rico

1967 ◽  
Vol 47 (3) ◽  
pp. 723-733 ◽  
Author(s):  
J. Mclachlan ◽  
M. Parke
Keyword(s):  
Puerto Rico ◽  
Fine Structure ◽  
Cell Division ◽  
Related Genus ◽  
Anatomical Features ◽  
Whole Cells ◽  
New Information ◽  
Electron Microscopes ◽  
Structure Investigations

The morphology and microanatomy of Platymonas impellucida sp.nov. have been investigated using light and electron microscopes and unusual stages of cell division studied. The anatomical features closely resemble those recently described for Platymonas convolutae (cf. Parke & Manton, 1967). As in that species the pyrenoid is penetrated from many directions by cytoplasmic canaliculi lined with the double plastid membrane but unlike that species a starch shell is not developed around the pyrenoid. In whole cells of P. impellucida therefore, it is extremely difficult, in most cases impossible, to detect the presence of the pyrenoid. This new information on the absence of a starch shell in a member of the Prasinophyceae is of importance since pyrenoid structure appears to be of major importance for taxonomic purposes. Apparent fusion stages have been shown to be a variation in vegetative division not previously encountered in the genus Platymonas.IntroductionRecent studies on members of the Prasinophyceae have assisted greatly in characterizing this class of green-pigmented algae although the limits are not as yet entirely defined. Fine-structure investigations have, in addition, elucidated certain features of generic significance. The genus Platymonas is now well described and can be unequivocally distinguished from Prasinocladus, a closely related genus. Previously these two genera were separated on the presence or absence of non-motile dendroid colonies, but such colonies are now known in both genera (Parke & Manton, 1967).The remaining significant diagnostic generic characteristic is the structure of the pyrenoid. In Platymonas the branched canaliculi invading the pyrenoid either from a direction facing the nucleus (Gibbs, 1962; Manton & Parke, 1965) or from many directions (Parke & Manton, 1967) contain cytoplasm rather than protrusions of the nucleus as in Prasinocladus (Parke & Manton, 1965).

Defects at Crystalline Interfaces

1970 ◽  
Vol 28 ◽  
pp. 506-507
Author(s):  
K. R. Kinsman ◽  
H. I. Aaronson
Keyword(s):  
Grain Boundaries ◽  
Single Phase ◽  
Relative Orientation ◽  
Interfacial Structure ◽  
Contrast Effects ◽  
Materials Analysis ◽  
Displacement Vectors ◽  
Transmission Electron ◽  
Line Defects ◽  
Diffraction Effects

Crystalline interfaces are of two basic types - interfaces in single phase solids separating grains of differing orientation (grain boundaries, sub-grain boundaries, twin boundaries), and interphase interfaces separating crystals which differ in crystal structure and/or composition, as well as relative orientation. Depending upon these variables a particular boundary will have more or less interfacial structure which can be resolved by transmission electron microscopy. The dislocations (line defects) which are imaged at boundaries by electron diffraction contrast effects may be unique to the boundary, i.e., have displacement vectors which are different from those of dislocations found in single phase materials. Analysis may be further complicated by extra diffraction effects such as superimposed Moire patterns (Fig. 1a and 2).

The (111)/(100) interface in cubic materials

1994 ◽  
Vol 52 ◽  
pp. 522-523
Author(s):  
Sundar Ramamurthy ◽  
C. Barry Carter
Keyword(s):  
Grain Boundaries ◽  
Coincident Site Lattice ◽  
Interface Plane ◽  
Polycrystalline Thin Films ◽  
Cubic Materials ◽  
Wide Range ◽  
Low Energies ◽  
Cubic System ◽  
The Stability ◽  
Microscopy Techniques

Descriptions of crystalline interfaces have concentrated on grain boundaries using the framework of the coincident-site-lattice (CSL) model. Within this framework, an interface-plane scheme can be formulated to describe all types of crystalline interfaces, homophase or heterophase. Low Σ values, the inverse density of CSL sites, are associated with boundaries with low energies. However, stable interfaces that cannot be described by such models are often found experimentally in thin-film, semi-bulk and bulk forms. The stability of such interfaces thus depends on factors other than the geometry of the interface.Crystallography of the (111)/(100) interface in the cubic system has been studied extensively in a wide range of materials using different electron-microscopy techniques. Recently, this interface has spurred interest in the growth of tri-crystal microstructures to study junctions in polycrystalline thin films where three identical grain boundaries meet along a line. In this paper we review the (111)/(100) interface showing different examples from our recent work.

Ab-Initio Theory of Initial Oxidation of Silicon (001) Surfaces

1997 ◽  
Vol 492 ◽  
Author(s):  
N. A. Modine ◽  
G. Zumbach ◽  
E. Kaxiras
Keyword(s):  
Oxygen Atom ◽  
Photoelectron Spectroscopy ◽  
Density Functional ◽  
Experimental Studies ◽  
Theoretical Work ◽  
Real Space ◽  
Initial Oxidation ◽  
Atomic Structures ◽  
Ab Initio Theory ◽  
Initial Oxygen

ABSTRACTThe oxidation of the Si(001) surface is an important process on both technological and theoretical grounds. Experimental studies have not provided a clear picture of even the relevant atomic structures during the initial stages of oxidation, while previous theoretical studies of these processes have yielded contradictory results. Using careful first principles total-energy calculations based on density functional theory, we study several mechanisms of incorporating a sub-monolayer coverage of oxygen into the characteristic p(2 × 1) dimer reconstruction of the Si(001) surface. Our recently developed Adaptive Coordinate Real-space Electronic Structure (ACRES) method allows us to obtain results that are adequately converged with respect to the numerous computational parameters associated with this difficult system. We compare our results with previous theoretical work and propose a physically motivated two step pathway for the initial incorporation of an oxygen atom into the dimerized surface. Based on our results, we can explain what formerly appeared to be puzzling Ultraviolet Photoelectron Spectroscopy measurements which indicated that each initial oxygen atom saturates two surface dangling bonds.

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