Transmission electron microscopy contrast enhancement

Kimura, Shirai and coworkers used two chiral dimeric porphyrins 95 and 96 to investigate their self-assembling behavior [162,163]. While incorporation into fibers made of the alkylamide derivatives of (fl,fl)-DACH, 95 formed stable well-resolved fibrous assemblies as visualized by transmission electron microscopy, the fluorescence of which was not quenched by external electron acceptors [162]. However, the induced CD was not detected indicating an inability of 95 to form chirally orientated aggregates under the applied conditions. In contrast, 96 was able to produce optically active inter molecular self-assemblies with an enhanced chiroptical response through the //-oxo bridging in an alkali solution, while intramolecular //-oxo dimer formation was excluded on the basis of steric reasons [163]. 

Despite these rapid developments, transmission electron microscopy could not possibly contribute significantly to coatings and polymer research until commercial machines became available. The first Siemens microscope was marketed in 1938 (35). followed the next year by a more advanced unit. In this country, RCA marketed its first unit in 1941 (36). Even with commercial equipment available, many other problems had to be overcome. The main difficulty was that of sample preparation. Sections had to be extremely thin to be penetrated sufficiently by the electron beam. Often contrast was not sufficient to form a suitable image. In 1939, the shadowing technique was developed to enhance contrast... 

Vesely and Finch used two radiation effects for contrast enhancement of the samples, which were examined by scanning transmission electron microscopy (i) differential formation of double bonds (through reactions such as (R-13)) in a component polymer, and (ii) differential mass... 

As in the field of condensed matter sciences, polymer research has made extensive use of conventional transmission electron microscopy (CTEM) ever since its invention. Polymer research focuses on materials that mainly consist of carbon and other light elements. These materials are relatively weak electron scatterers and therefore give low mass thickness and phase contrast. Mass thickness contrast may be enhanced using an objective aperture, staining, and/or low... 

Figure 4.15. Transmission electron microscopy micrographs of a sectioned microporous membrane show little detail of the structure due to the low electron scattering of the polymer (A). Treatment with an unsaturated surfactant followed by osmium staining results in sections with enhanced contrast, which permits...

Figure 4.22. Transmission electron microscopy micrographs of sectioned industrial tire cords are prepared by the ebonite method to enhance the contrast of the various structures and to harden the adhesive and the rubber for sectioning. Fiber cross sections, two adhesive layers (RFL), and the rubber (R) are shown by TEM.

Figure 5.70. A phase contrast optical micrograph (A) of an impact modified nylon shows the fine dispersion of modifier in the matrix. Transmission electron microscopy micrographs of a cryosection, stained with ruthenium tetroxide (B and C), show more detail and finely dispersed subinclusions (arrows) within the elastomeric phase. Scanning transmission electron microscopy (D) of an unstained cryosection shows less dense regions in a darker background due to mass loss of the rubber phase during exposure to the electron beam, resulting in contrast enhancement.

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