Misfit dislocations in heteroepitaxial systems with low dislocation density

1978 ◽  
Vol 36 (1) ◽  
pp. 132-133
Author(s):  
W. Hagen ◽  
H. Strunk
Keyword(s):  
Electron Microscopy ◽  
Dislocation Density ◽  
Misfit Dislocations ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
Transmission Electron ◽  
Low Dislocation Density ◽  
Heteroepitaxial Layers ◽  
Transparent Area ◽  
Electron Transparent Area

The growth of heteroepitaxial layers causes stress across the interface which in a certain range of layer thickness may he relaxed by the formation of misfit dislocations at the interface. Systematic investigations of such misfit structures by transmission electron microscopy (TEM) have previously heen conducted only on systems with a relatively large misfit parameter f, i.e. with a high dislocation density. However, this case presents difficulties in the analysis because of the complexity of the dense structures.Interfaces containing a low density of misfit dislocations, e.g. heteroepitaxial systems with low misfit, should consequently be investigated. High voltage electron microscopy (HVEM) enables us to study specimens of several μm in thickness and offers decisive advantages over 100 kV TEM: i) generally, specimens can he prepared by thinning the substrate only, ii) thick foils are mechanically stable, which allows the preparation of specimens with an electron transparent area of several mm2.We report here new results on the initial formation of misfit dislocation structures in the heteroepitaxial system Ge on GaAs (f = 0.074%).

scholarly journals Some Current and Future Trends of High Voltage Transmission Electron Microscopy

1973 ◽  
Vol 31 ◽  
pp. 2-3
Author(s):  
Gareth Thomas
Keyword(s):  
Electron Microscopy ◽  
High Voltage ◽  
Materials Science ◽  
Future Trends ◽  
Light Elements ◽  
Special Effects ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
Transmission Electron ◽  
Resolution Level

The Optimum Voltages for Electron Microscopy – The advantages of high voltage electron microscopy are now well established, and many applications, such as use of environmental cells both in metallurgy and biology, are now possible. However recent experiments at Toulouse indicate that except for light elements, there is no appreciable gain in transmission for a given resolution level as the energy is increased above 1 MeV (see Fig. 1). These results are not as optimistic as theory might indicate. Special effects such as critical voltages above 1 MeV are of interest, but knock-on radiation damage imposes limitations on many applications. Thus it would appear that 1 MeV is a reasonable upper limit for most applications in materials science.

Observations on Developing Blood Vessels in Rat Spinal Cord—A High Voltage Electron Microscopy Study

1974 ◽  
Vol 32 ◽  
pp. 66-67
Author(s):  
Richard S. Hannah
Keyword(s):  
Electron Microscopy ◽  
Spinal Cord ◽  
High Voltage ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
High Voltage Electron Microscopy ◽  
Thin Sections ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Transmission Electron

The formation of junctional complexes between endothelial cell processes was examined in rat spinal cords, from age birth to six weeks. Segments of spinal cord were removed from the region of the cervical enlargement and fixed. For comparative purposes, animals from each time group were subdivided into groups, fixed by either immersion or perfusion with an aldehyde combination in sodium cacodylate buffer and embedded in Araldite. Thin sections were examined by conventional transmission electron microscopy. Thick sections (0.5μ - 1.0μ) were stained with uranyl magnesium acetate for four hours at 60°C and lead citrate for 30 mins. and examined in the AEI Mark II High Voltage Electron Microscope.

Detection efficiency and estimation of the performance of high voltage STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 84-85
Author(s):  
A. Ishikawa ◽  
C. Morita ◽  
M. Hibino ◽  
S. Maruse
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radiation Damage ◽  
High Voltage ◽  
Detection Efficiency ◽  
Beam Current ◽  
High Energy ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
Transmission Electron

One of the problems which are met in conventional transmission electron microscopy (CTEM) at high voltages is the reduction of the sensitivity of photographic films for high energy electron beams, resulting in the necessity of using high beam current. This cancels out an advantage of high voltage electron microscopy which is otherwise expected from the reduction of the inelastic scattering in the specimen, that is the reduced radiation damage of the specimen during observations. However, it is expected that the efficiency of the detector of scanning transmission electron microscopy (STEM) can be superior to that of CTEM, since the divergence of the electron beam in the detecting material does not affect the quality of the image. In addition to observation with less radiation damage, high voltage STEM with high detection efficiency is very attractive for observations of weak contrast objects since the enhancement of the contrast (which is an important advantage of STEM) is easily realized electrically.

Comparison of Images of Crystalline Specimens by Energy-Filtering TEM at 80 keV and CTEM at 200 keV

1990 ◽  
Vol 48 (2) ◽  
pp. 62-63
Author(s):  
A. Bakenfelder ◽  
L. Reimer ◽  
R. Rennekamp
Keyword(s):  
Electron Microscopy ◽  
Energy Loss ◽  
Chromatic Aberration ◽  
Biological Tissues ◽  
Energy Window ◽  
High Voltage Electron Microscopy ◽  
Energy Filtering ◽  
Voltage Electron ◽  
Transmission Electron ◽  
Crystalline Films

One advantage of energy-filtering electron microscopy (EFEM) is to avoid the chromatic aberration of conventional transmission electron microscopy (CTEM) by the mode of electron spectroscopic imaging (ESI) using either zero-loss filtering of unscattered and elastically scattered electrons or a narrow selected energy window at the most probable loss of the electron-energy-loss spectrum (EELS). Chromatic aberration can also be reduced by high-voltage electron microscopy (HVEM). Comparisons of ESI at 80 keV and CTEM at 200 keV have already been reported for biological tissues. In this contribution we compare the imaging of evaporated crystalline films with ESI at 80 keV in a ZEISS EM902 and with CTEM at 200 keV in a Hitachi H800/NA.Zero-loss filtering at 80 keV can be applied for maximum mass-thicknesses of x=ρt≃150 μg/cm2 where the zero-loss transmission falls below 0.001 and an energy window at the most-probable energy loss can be used below ≃300 μg/cm2. Inelastic scattering preserves the Bragg contrast.

Extracellular matrix morphogenesis: HVEM analysis

1987 ◽  
Vol 45 ◽  
pp. 574-577
Author(s):  
David E. Birk ◽  
Robert L. Trelstad
Keyword(s):  
Electron Microscopy ◽  
Molecular Assembly ◽  
High Voltage Electron Microscopy ◽  
Tissue Specific ◽  
Voltage Electron ◽  
Transmission Electron ◽  
Corneal Fibroblasts ◽  
Multistep Process ◽  
Collagen Molecules ◽  
Supramolecular Aggregates

Matrix morphogenesis requires the synthesis, assembly and deposition of collagen molecules in a tissue specific manner. Collagen fibrillogenesis is a multistep process involving both intracellular and extracellular assembly reactions. Collagen synthesis, molecular assembly and formation of supramolecular aggregates occurs within a series of well defined cytoplasmic compartments while the assembly and deposition of the newly synthesized collagen fibrils, fibril bundles and tissue specific collagen macroaggregates occurs within a series of extracellular compartments defined by the fibroblast.In the studies described here we will focus our attention on the cellular influences involved in the assembly of collagen molecules into fibrils, fibril bundles and tissue specific macroaggregates. The chick tendon and corneal fibroblasts partition the extracellular space during morphogenesis, forming at least three compartments. These extracytoplasmic compartments have been described using high voltage electron microscopy of thick sections and serial thick sections as well as by conventional transmission electron microscopy.

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