Domains in single crystals of poly-4-methyl-pentene-1

1987 ◽  
Vol 45 ◽  
pp. 488-489
Author(s):  
P. Pradère ◽  
J.-F. Revol ◽  
R. St. John Manley
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Single Crystals ◽  
Solution Concentration ◽  
Dark Field ◽  
Dilute Solution ◽  
Contrast Imaging ◽  
Slow Cooling ◽  
Carbon Coated ◽  
Isothermal Crystallisation

Polymer single crystals are generally considered to be structurally homogeneous. In this paper it is shown that in a given single crystal of poly-4-methyl-pentene-1 (P4MP1) there exist narrowly delimited domains that give rise to different electron diffraction (ED) patterns. The shape and location of these domains is characterized by diffraction contrast imaging in the dark field (DF) mode.Monolayer single crystals of P4MP1 polymorphs I and III were prepared in dilute solution (concentration ranging from 0.01 to 0.05%). Form I was obtained by slow cooling of a hexadecane solution whereas form III was prepared by isothermal crystallisation in xylene at 60°C. Crystals were deposited on carbon coated grids and observed with a Philips EM 400 T electron microscope operated at 120 kV. The crystals are very radiation sensitive and the total end point dose, measured by the fading of the ED pattern is 27 C m-2.

Spherulite morphology in thin films of natural rubber

1962 ◽  
Vol 270 (1341) ◽  
pp. 232-241 ◽  
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Single Crystals ◽  
Growth Mechanism ◽  
Electron Irradiation ◽  
Electron Diffraction Data ◽  
Dilute Solution ◽  
Spherulite Morphology

Crystalline ‘spherulites’ grown in ultra-thin films of natural rubber at — 26 °C were examined in the electron microscope. The spherulites form hollow domes, like blisters in the film, which collapse under electron irradiation producing remarkable fibre-like patterns of folds and creases. Within the spherulite, crystalline and amorphous regions coexist and the former appear to grow to a preferred thickness of a few hundred Angstroms with the molecular chains oriented perpendicular to the film. The molecules are thus almost certainly folded as in polymer single crystals grown from dilute solution. Electron diffraction data suggest that relatively large regions of the spherulite correspond to single crystals. A growth mechanism for the spherulites is proposed.

Spherulite Morphology in Thin Films of Natural Rubber

1965 ◽  
Vol 38 (1) ◽  
pp. 33-44
Author(s):  
E. H. Andrews
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Single Crystals ◽  
Growth Mechanism ◽  
Electron Irradiation ◽  
Electron Diffraction Data ◽  
Dilute Solution ◽  
Spherulite Morphology

Abstract Crystalline ‘spherulites’ grown in ultra-thin films of natural rubber at − 26° C were examined in the electron microscope. The spherulites form hollow domes, like blisters in the film, which collapse under electron irradiation producing remarkable fiber-like patterns of folds and creases. Within the spherulite, crystalline and amorphous regions coexist and the former appear to grow to a preferred thickness of a few hundred angstroms with the molecular chains oriented perpendicular to the film. The molecules are thus almost certainly folded as in polymer single crystals grown from dilute solution. Electron diffraction data suggest that relatively large regions of the spherulite correspond to single crystals. A growth mechanism for the spherulites is proposed.

The decomposition of magnesium hydroxide in an electron microscope

1958 ◽  
Vol 247 (1250) ◽  
pp. 346-352 ◽  
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Single Crystals ◽  
Magnesium Oxide ◽  
Magnesium Hydroxide ◽  
Basal Plane ◽  
Morphological Changes ◽  
Water Molecules ◽  
Two Stages

The beam of an electron microscope has been used to dehydrate single crystals of magnesium hydroxide to magnesium oxide. Electron diffraction photographs and electron micrographs were taken at various stages to follow the crystallographic and morphological changes which accompany decomposition. The decomposition may be considered to occur in two stages. First, there is a small shrinkage in the basal plane, and the resulting strain causes a maze of cracks in the crystal. This change is followed by a collapse of the planes down the original [0001] of magnesium hydroxide. The collapse is controlled by the migration of water molecules from between the planes to a surface where they can escape. The product is a highly oriented aggregate of micro-crystallites of magnesium oxide. More intense irradiation in the electron beam occasionally causes bulk movement of the solid.

Direct Observation of the Surface Topography of Single Crystals in a Transmission Electron Microscope

1981 ◽  
Vol 39 ◽  
pp. 208-211
Author(s):  
G. Lehmpfuhl ◽  
Y. Uchida
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Surface Topography ◽  
Single Crystals ◽  
Dynamic Effect ◽  
Thickness Variation ◽  
Crystal Thickness ◽  
Kinematic Effect ◽  
Diffraction Patterns ◽  
Small Change

From the analysis of convergent-beam electron diffraction patterns it is well known that the intensity of some reflections may become most sensitive to the crystal thickness variation at special conditions for thickness and orientation. This can be understood as a dynamic effect as well as a kinematic effect of electron diffraction. Using such a diffracted beam for imaging, a small change in thickness of a single crystal can be observed in an electron microscope. At the beginning of the application of this technique only weak beams were used for imaging the surface topography of undistorted single crystals. Thickness differences down to the atomic level could be detected in darkfield micrographs of MgO and Au. However, the intensity of the weak beams was so low that long exposure times up to 2 minutes were necessary to record a micrograph at a magnification of 20,000. This magnification is the upper limit for the weak-beam darkfield technique for reasons of stability of the electron microscope. The thickness contrast can be explained already by the kinematical theory of electron diffraction.

Electron microscopic investigation of the structure and morphology of syndiotactic polypropylene

1989 ◽  
Vol 47 ◽  
pp. 358-359
Author(s):  
Andrew J. Lovinger ◽  
Bernard Lotz ◽  
Don D. Davis
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Dark Field ◽  
Microscopic Investigation ◽  
Electron Microscopic Investigation ◽  
Dilute Solution ◽  
Electron Microscopic ◽  
Syndiotactic Polypropylene ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron

In contrast to its isotactic isomer, syndiotactic polypropylene has received only little attention. Our main source of understanding of its structure is the X-ray study by Conradini et al., who found the chains to have a (t2g2)2 conformation (corresponding to a 4∗2/1 helix with molecular repeat 0.74 nm), and to be packed in a C-centered unit cell as shown in the left side of Fig. 1. We have recently begun a study of the structure, crystallization, and morphology of syndiotactic polypropylene using electron microscopy and diffraction. Here we concentrate specifically on the electron-diffraction evidence as a function of temperature, in order to obtain an understanding of the evolution and variation of structure in this polymer.Thin films of syndiotactic polypropylene (synthesized by Dr. R. E. Cais as reported previously) were prepared by casting from dilute solution in xylenes at ca. 140°c onto freshly cleaved mica substrates. Following evaporation of the solvent, they were melted and then isothermally crystallized at a variety of temperatures. After shadowing with Pt/C and coating with carbon, they were floated off their substrates for examination by transmission electron microscopy (bright- and dark-field) and selected-area electron diffraction at 100-200 keV.

Struktur und thermisches Verhalten von Wachstumszwillingen in dünnen kubisch flächenzentrierten Metallschichten

1965 ◽  
Vol 20 (9) ◽  
pp. 1201-1207 ◽  
Author(s):  
H. Schlötterer
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Hexagonal Phase ◽  
Stacking Faults ◽  
Dark Field Image ◽  
Dark Field ◽  
Periodic Lattice ◽  
Double Diffraction ◽  
Polycrystalline Films ◽  
Matrix Orientation

Single crystal films prepared by evaporation of silver, gold, copper, and nickel on heated cleaved rocksalt crystals and polycrystalline films of silver, gold, copper, platinum, aluminum, and nickel have been studied by transmission electron microscopy and electron diffraction. By means of electron microscope dark-field image and selected area diffraction technique the existence of small growth twins in the films is shown. Extra spots observed in the electron diffraction diagram can be explained partly as spots of the four twin orientations, partly as arising from double diffraction of the (100) matrix orientation and of a twin orientation. In the case of polycrystalline films the double diffraction mechanism results in additional diffraction rings seeming not to belong to the normal face-centred cubic lattice. The assumption of an hexagonal phase or of stacking faults or of periodic lattice defects cannot explain all the extra spots and additional rings.The changing diffraction contrast of thick and thin microtwins obviously depends on the different reflection conditions in the electron microscope. It is shown that it is very complicated to distinguish stacking faults from microtwins, but some criteria of distinction are given.By means of a heating stage the single crystals have been heated in the electron microscope up to more than 1000 °C. The thermal behaviour of the twins has been studied in detail. It can be observed that up to 95% of the twins become invisible by transformation from the twin orientation to the (100) matrix orientation. It is concluded from the experiments that the transformation nucleates at the top or bottom of the thin films. Nevertheless more than 1013 twins and stacking faults per cm3 remain unchanged inspite of heating to temperatures near the melting point of the bulk metal.

The Formation and Utility of Sub-Angstrom to Nanometer-Sized Electron Probes in the Aberration-Corrected Transmission Electron Microscope at the University of Illinois

2010 ◽  
Vol 16 (2) ◽  
pp. 183-193 ◽  
Author(s):  
Jianguo Wen ◽  
James Mabon ◽  
Changhui Lei ◽  
Steve Burdin ◽  
Ernie Sammann ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Transmission Electron Microscope ◽  
Spherical Aberration ◽  
Real Space ◽  
Dark Field ◽  
Atomic Scale ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractWe evaluate the probe forming capability of a JEOL 2200FS transmission electron microscope equipped with a spherical aberration (Cs) probe corrector. The achievement of a real space sub-Angstrom (0.1 nm) probe for scanning transmission electron microscopy (STEM) imaging is demonstrated by acquisition and modeling of high-angle annular dark-field STEM images. We show that by optimizing the illumination system, large probe currents and large collection angles for electron energy loss spectroscopy (EELS) can be combined to yield EELS fine structure data spatially resolved to the atomic scale. We demonstrate the probe forming flexibility provided by the additional lenses in the probe corrector in several ways, including the formation of nanometer-sized parallel beams for nanoarea electron diffraction, and the formation of focused probes for convergent beam electron diffraction with a range of convergence angles. The different probes that can be formed using the probe corrected STEM opens up new applications for electron microscopy and diffraction.

Utilizing Dark Field Electron Microscopy to Produce Lantern Slides

1974 ◽  
Vol 32 ◽  
pp. 116-117
Author(s):  
J. N. Meador ◽  
C. N. Sun ◽  
H. J. White
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Dark Field ◽  
Limiting Factor ◽  
Clinical Laboratories ◽  
Field Electron ◽  
Time Element ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Dark Field Micrographs

The electron microscope is being utilized more and more in clinical laboratories for pathologic diagnosis. One of the major problems in the utilization of the electron microscope for diagnostic purposes is the time element involved. Recent experimentation with rapid embedding has shown that this long phase of the process can be greatly shortened. In rush cases the making of projection slides can be eliminated by taking dark field electron micrographs which show up as a positive ready for use. The major limiting factor for use of dark field micrographs is resolution. However, for conference purposes electron micrographs are usually taken at 2.500X to 8.000X. At these low magnifications the resolution obtained is quite acceptable.

Sign in / Sign up

Export Citation Format

Share Document