Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

A method for direct measurement of specimen noise in HREM images

1993 ◽  
Vol 51 ◽  
pp. 458-459
Author(s):  
Sidnei Paciornik ◽  
Roar Kilaas ◽  
Ulrich Dahmen ◽  
Michael Adrian O'Keefe
Keyword(s):  
Random Noise ◽  
Image Interpretation ◽  
Thin Foil ◽  
High Resolution Electron Microscopy ◽  
Black Dot ◽  
Atomic Column ◽  
Amorphous Oxide ◽  
Resolution Electron ◽  
Imaging Conditions ◽  
Image Simulations

High resolution electron microscopy (HREM) is a primary tool for studying the atomic structure of defects in crystals. However, the quantitative analysis of defect structures is often seriously limited by specimen noise due to contamination or oxide layers on the surfaces of a thin foil.For simple monatomic structures such as fcc or bcc metals observed in directions where the crystal projects into well-separated atomic columns, HREM image interpretation is relatively simple: under weak phase object, Scherzer imaging conditions, each atomic column is imaged as a black dot. Variations in intensity and position of individual image dots can be due to variations in composition or location of atomic columns. Unfortunately, both types of variation may also arise from random noise superimposed on the periodic image due to an amorphous oxide or contamination film on the surfaces of the thin foil. For example, image simulations have shown that a layer of amorphous oxide (random noise) on the surfaces of a thin foil of perfect crystalline Si can lead to significant shifts in image intensities and centroid positions for individual atomic columns.

Atomic chemistry by HREM and image simulations?

1986 ◽  
Vol 44 ◽  
pp. 828-829
Author(s):  
J.M. Howe ◽  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Resolution Electron ◽  
Image Simulations

The technique of high-resolution electron microscopy (HREM) is invaluable to the materials scientist because it allows examination of microstructural features at levels of resolution that are unobtainable by most other methods. Although the structural information which can be determined by HREM and accompanying image simulations has been well documented in the literature, there have only been a few cases where this technique has been used to reveal the chemistry of individual columns or planes of atoms, as occur in segregated and ordered materials.

Observation of the CdTe-GaAs Interface by High Resolution Electron Microscopy

1984 ◽  
Vol 37 ◽  
Author(s):  
N. Otsuka ◽  
L. A. Kolodziejski ◽  
R. L. Gunshor ◽  
S. Datta ◽  
R. N. Bicknell ◽  
...  
Keyword(s):  
High Resolution ◽  
Film Growth ◽  
Substrate Surface ◽  
High Resolution Electron Microscopy ◽  
Gaas Substrates ◽  
Resolution Electron ◽  
Interfacial Structures ◽  
Substrate Preheating ◽  
High Resolution Electron Microscope

AbstractCdTe films have been grown on GaAs substrates with two types of interfaces - one with the epitaxial relation (111)CdTe║ (100)GaAs and the other with (100)CdTe║ (100)GaAs,. High resolution electron microscope observation of the two types of interfaces was carried out in order to determine the role of the substrate surface microstructure in determining the epitaxy. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin oxide layer (∼10 Å in thickness) between the two crystals. These observations suggest that details of the substrate preheating cycle prior to film growth is the principle factor in determining which epitaxial relation occurs in this system. The relation between interfacial structures and the origin of the two epitaxial relations is discussed.

Crystal Structure of and Defects in the Pentacene Thin Film Phase

2002 ◽  
Vol 734 ◽  
Author(s):  
Lawrence F. Drummy ◽  
Paul K. Miska ◽  
David C. Martin
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Low Voltage ◽  
Field Effect Transistors ◽  
High Resolution Electron Microscopy ◽  
Orthorhombic Symmetry ◽  
Extended Defects ◽  
X Ray Diffraction ◽  
Voltage Electron ◽  
Resolution Electron

The aromatic hydrocarbon pentacene is currently under investigation for use as the active layer in electronic devices such as thin film field effect transistors. We have used X-Ray Diffraction (XRD), Electron Diffraction (ED), Low Voltage Electron Microscopy (LVEM), High Resolution Electron Microscopy (HREM) and molecular modeling to investigate the thin film phase of pentacene. We will report the orthorhombic symmetry and lattice parameters of the thin film phase measured experimentally from these techniques. The structure of extended defects such as dislocations and grain boundaries will influence the electrical and mechanical characteristics of the films. Here we show a direct image of an edge dislocation in the thin film phase and discuss the way in which the lattice accommodates the defect.

Misfit Dislocations at II-VI/GaAs Interfaces

1990 ◽  
Vol 183 ◽  
Author(s):  
A. F. Schwartzman
Keyword(s):  
Lattice Mismatch ◽  
High Resolution Electron Microscopy ◽  
Interfacial Structure ◽  
Misfit Dislocations ◽  
Extended Defects ◽  
Partial Dislocations ◽  
Resolution Electron ◽  
Before And After ◽  
Slip Planes ◽  
Efficient Type

AbstractHigh-resolution electron microscopy -is used to characterize the defect structure of CdTe/GaAs and ZnTe/GaAs heterojunctions before and after annealing. For as-deposited films, a variety of defects exist both in the form of perfect misfit dislocations at the interface and extended defects into the thin film. The extended defects result from dissociation of 60° dislocations and reactions between perfect and partial dislocations lying on intersecting slip planes. The annealed interfaces consist of a periodic array of perfect edge Lomer dislocations, the most efficient type of misfit dislocation for accomodating the lattice mismatch, 14.6 % for CdTe/GaAs and 8 % for ZnTe/GaAs. In both cases, the spacing between dislocations corresponds to the value predicted for completely strain-free thin fims, 31 and 54 Å for CdTe and ZnTe respectively. This paper concentrates on the different dislocation reactions which transform the interfacial structure from the as-deposited case to the annealed case.

Trends in Atomic Resolution Electron Microscopy

1994 ◽  
Vol 332 ◽  
Author(s):  
David J. Smith ◽  
M.R. Mccartney
Keyword(s):  
Electron Microscopy ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Operating Conditions ◽  
Atomic Scale ◽  
Irradiation Damage ◽  
Image Recording ◽  
Exit Surface ◽  
Resolution Electron ◽  
Image Simulations

ABSTRACTStructural information on the atomic scale is readily accessible from thin samples using the technique of high-resolution electron microscopy. Electron micrographs recorded under well-defined operating conditions can be directly interpreted in terms of atomic arrangements around defects of interest such as dislocations and interfaces. Digital image recording with slow-scan CCD cameras and quantitative comparisons with image simulations based on structural models are starting to lead to improved accuracy and reliability in structure determinations. Techniques based upon holographic methods are utilizing the superior illumination coherence of the field emission electron source to enhance resolution beyond the conventional extended Scherzer limit. Innovative methods for combining image and diffraction pattern information are also leading to improved levels of resolution for periodic objects. Care is needed to ensure that electron irradiation damage and surface cleanliness do not impose unnecessary restrictions on the details that can be extracted from recorded micrographs. It is proposed that the complex wavefunction emerging from the exit-surface of the sample should be considered as a basis for comparing the differences between experimental micrographs and image simulations.

Electron Microscopy Observations on the Role of Twinning in the Evolution of Microstructures

2002 ◽  
Vol 8 (4) ◽  
pp. 247-256 ◽  
Author(s):  
U. Dahmen ◽  
C.J.D. Hetherington ◽  
V. Radmilovic ◽  
E. Johnson ◽  
S.Q. Xiao ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Phase Transformations ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Equilibrium Shape ◽  
High Resolution Electron Microscopy ◽  
Resolution Electron ◽  
Multiple Twinning

Twinning plays an important role in phase transformations and can have significant effects on microstructural evolution. Different roles of twinning in the development of microstructures during precipitation and phase transformations are reviewed and illustrated with examples from investigations by high-resolution electron microscopy, including the effect of multiple twinning on the development of Ge precipitates in Al-Ge and Ag-Ge alloys, the twin dissociation of grain boundaries in Au, the formation of hexagonal Si at twin intersections and the effect of twin boundaries on the equilibrium shape of Pb inclusions in Al.

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