Structure of the Σ=5 (310) interface in NiAl

1993 ◽  
Vol 51 ◽  
pp. 984-985
Author(s):  
Richard W. Fonda ◽  
David E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Point Defects ◽  
Low Temperatures ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Embedded Atom ◽  
Resolution Electron ◽  
Antisite Defects ◽  
Simulated Images

The atomic structure of the Σ=5 [001] (310) grain boundary in NiAl was examined by high resolution electron microscopy and multislice image simulation. As in most other intermetallic compounds, the grain boundaries in NiAl are intrinsically brittle at low temperatures. Although there have been few studies on this alloy, the energies of NiAl grain boundaries have been calculated using embedded atom potentials for both stoichiometric and non-stoichiometric structures. These studies are consistent with the results of Bradley and Taylor, which indicate that nickel-rich compositions result from nickel antisite defects on the aluminum sublattice, while aluminum-rich compositions produce constitutional vacancies on the nickel sublattice, and with recent field ion microscopy results on nickel-rich alloys.The Σ=5 grain boundary was prepared by diffusion bonding at 1000 °C. A JEOL 4000EX was used for HREM imaging and the NUMIS multislice simulation program was used to simulated images. Analysis of these images considered the effects of grain boundary expansion, rigid body displacements along the boundary, grain boundary stoichiometry, and point defects at the boundary.

Σ =13 tilt grain boundary in silicon bicrystal

1990 ◽  
Vol 48 (4) ◽  
pp. 562-563
Author(s):  
M.J. Kim ◽  
Y.L. Chen ◽  
R.W. Carpenter ◽  
J.C. Barry ◽  
G.H. Schwuttke
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Rotation Axis ◽  
Czochralski Method ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Simulation Techniques ◽  
Resolution Electron ◽  
The Common ◽  
Tilt Grain Boundary

The structure of grain boundaries (GBs) in metals, semiconductors and ceramics is of considerable interest because of their influence on physical properties. Progress in understanding the structure of grain boundaries at the atomic level has been made by high resolution electron microscopy (HREM) . In the present study, a Σ=13, (510) <001>-tilt grain boundary in silicon was characterized by HREM in conjunction with digital image processing and computer image simulation techniques.The bicrystals were grown from the melt by the Czochralski method, using preoriented seeds. Specimens for TEM observations were cut from the bicrystals perpendicular to the common rotation axis of pure tilt grain boundary, and were mechanically dimpled and then ion-milled to electron transparency. The degree of misorientation between the common <001> axis of the bicrystal was measured by CBED in a Philips EM 400ST/FEG: it was found to be less than 1 mrad. HREM was performed at 200 kV in an ISI-002B and at 400 kv in a JEM-4000EX.

Characterization of structural units in tilt grain boundaries

1992 ◽  
Vol 50 (1) ◽  
pp. 120-121
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Structural Units ◽  
Symmetric Tilt ◽  
Resolution Electron ◽  
Special Cases ◽  
High Resolution Electron Microscope

General tilt grain boundaries can be viewed in terms of small structural units of varying complexity. High-resolution electron microscope (HREM) images of these boundaries in many materials show this repetitive similarity of the atomic structure at the boundary plane. The structure of particular grain boundaries has been examined for several special cases and commonly observed configurations include symmetric tilt grain boundaries and asymmetric tilt grain boundaries with one grain having a prominent, low-index facet. Several different configurations of the boundary structure may possibly occur, even in the same grain boundary. There are thus many possible ways to assemble the basic structural units to form a grain boundary. These structural units and their distribution have traditionally been examined by high-resolution electron microscopy. The images of the projection of the atomic columns (or the tunnels between atomic columns) providing a template for constructing “ball-and-stick ” models of the interface.

The Atomic Structure of Mosaïc Grain Boundary Dislocations in GaN Epitaxial Layers

1999 ◽  
Vol 589 ◽  
Author(s):  
V. Potin ◽  
G. Nouet ◽  
P. Ruterana ◽  
R.C. Pond
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Atomic Structure ◽  
High Resolution Electron Microscopy ◽  
Anisotropic Elasticity ◽  
Epitaxial Layers ◽  
Threading Dislocations ◽  
Image Simulation ◽  
Resolution Electron

AbstractThe studied GaN layers are made of mosaYc grains rotated around the c-axis by angles in the range 0-25°. Using high-resolution electron microscopy, anisotropic elasticity calculations and image simulation, we have analyzed the atomic structure of the edge threading dislocations. Here, we present an analysis of the Σ = 7 boundary using circuit mapping in order to define the Burgers vectors of the primary and secondary dislocations. The atomic structure of the primary ones was found to exhibit 5/7 and 8 atom cycles.

Grain Boundary Transformations in Bi-Doped Copper

1991 ◽  
Vol 238 ◽  
Author(s):  
Elsie C. Urdaneta ◽  
David E. Luzzi ◽  
Charles J. McMahon
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Treatment Time ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

ABSTRACTBismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.

Atomic Resolution Studies of Tilt Grain Boundaries in NiO

1985 ◽  
Vol 60 ◽  
Author(s):  
K. L. Merkle ◽  
J. F. Reddy ◽  
C. L. Wiley ◽  
David J. Smith ◽  
G. J. Wood
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Mirror Symmetry ◽  
High Resolution Electron Microscopy ◽  
Atomic Resolution ◽  
High Angle ◽  
Structural Units ◽  
Atomic Structures ◽  
Resolution Electron

AbstractThe atomic structures of a number of <001> high-angle tilt grain boundaries in NiO have been studied by high-resolution electron microscopy (HREM). Crystal 1inity is always maintained right up to the grain boundary (GB). Grain boundary planes bounded by a (100)-plane are preferred, however symmetrical facets are also found at each misorientation. A tendency to match atomic planes across the GB is not only observed in symmetrical, but also in asymmetrical GBs. Structural units can be clearly recognized in symmetrical GBs. Contrast differences suggest that a multiplicity of structural units exists for some GB configurations. Frequently symmetric GBs also show deviations from mirror symmetry. Multislice simultations indicate that the image contrast associated with HREM GB images is not particularly sensitive to GB relaxation.

Structure of the ∑=3 (111) Grain Boundary in Cu-1.5%Sb

1992 ◽  
Vol 295 ◽  
Author(s):  
Richard W. Fonda ◽  
David E. Luzzi
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Auger Electron ◽  
Preliminary Investigation ◽  
High Resolution Electron Microscopy ◽  
Transmission Electron ◽  
Resolution Electron

AbstractGrain boundaries in quenched and aged Cu-i.5%Sb were examined with Auger electron microscopy, transmission electron microscopy, and high resolution electron microscopy. The ∑=3 grain boundaries are strongly faceted, with the facets lying primarily along the coincident (111) planes of the two grains. The grain boundaries are enriched in antimony, as demonstrated by both AES and HREM. HREM images of the ∑=3 (111) ║ (111) grain boundary differ from those of the Cu-Bi ∑ =3 (111) ║ (111) grain boundary in the lack of a significant grain boundary expansion to accommodate the excess solute at the boundary. A preliminary investigation of the atomic structure of the ∑=3 (111) ║ (111) facet by HREM and multislice calculations is presented.

Effect of Cu and Al Substitutions on the Microstructure of R-Fe-B Magnets

1991 ◽  
Vol 232 ◽  
Author(s):  
Y. J. Zhang ◽  
L. Withanawasam ◽  
G. C. Hadjipanayis ◽  
A. Kim
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Secondary Phases ◽  
Al Substitution ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Melt Spun

ABSTRACTThe coercivity of melt-spun Pr-Fe-B ribbons was found to increase with the addition of Cu and Al. The change in size and shape of grains with Cu and Al substitution were investigated by transmission eletron microscopy (TEM) and the grain boundary structure was further examined with high resolution electron microscopy (HREM). For small substitutions only “disturbed lattice” regions were observed at most of the grain boundaries. Secondary phases rich in the added elements were observed mostly at tripple grain boundaries and sometimes at grain boundaries in samples with larger amounts of substitution. The grain size in the substituted samples does not decrease much with further substitution. However, the shape of grains changes from polyhexagons to facets. The enhancement in coercivity can be explained by the grain size reduction and the modification of microstructure at the grain boundary regions.

Anti-Site Bonds and the Structure of Interfaces in SiC

1990 ◽  
Vol 183 ◽  
Author(s):  
P. Pirouz ◽  
J. Yang
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Compound Semiconductors ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Dangling Bonds ◽  
Resolution Electron ◽  
Elemental Semiconductors

AbstractHigh resolution electron microscopy has been used to study the structure of the 3C/6H interface, Σ,=3 {111}and Σ.=3 {112}grain boundaries in 3C-SiC. In SiC, as in other compound semiconductors, anti-site bonds occur in a variety of defects. These are high energy bonds comparable to that of dangling bonds. But, while dangling bonds at the grain boundaries may be eliminated by reconstruction just as in elemental semiconductors, it may not be possible to avoid anti-site bonds.These problems are discussed for the Σ=3 {112} grain boundary, where the structures proposed for Ge and Si are used as starting models for SiC.

Time-resolved high-resolution electron microscopy of grain migration process in MgO films

1996 ◽  
Vol 54 ◽  
pp. 674-675
Author(s):  
T. Kizuka ◽  
M. Iijima ◽  
N. Tanaka
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
High Resolution Electron Microscopy ◽  
Video Tape ◽  
Grain Boundary Migration ◽  
Time Resolved ◽  
Resolution Electron

High-resolution electron microscopy (HREM) has been employed intensively to analyze the atomic structures of grain boundaries and interfaces having two dimensional structures inside polycrystalline and composite materials. Furthermore time-resolved HREM (TRHREM) is required to analyze the behavior of grain boundaries and interfaces at atomic scale. The grain boundary migration, which is a typical grain boundary behavior, is a fundamental process relating to structural stability of polycrystalline materials. The mechanism of the migration has been still unknown.In the present study, the variation of atomic arrangement at the grain boundary migration of a MgO [001]Σ5 boundary was analyzed by TRHREM.Magnesium oxide polycrystalline films were prepared by vacuum-deposition on air-cleaved (001) surfaces of sodium chloride at 300°C. TRHREM was carried out at room temperature using a 200-kV electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder. The spatial resolution of the system was 0.2 nm at 200 kV and the time resolution was 1/60 s. Electron beam density was 30 A/cm2.

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