Microscopy, replication techniques

Scanning electron microscopy and replication techniques provide information concerning the outer surfaces of the sample only. Accurate electron microprobe analyses require smooth surfaces. To use these techniques profitably, it is therefore necessary to incorporate these requirements into the experimental design, since the interfaces of interest are often below the external particle boundary. To investigate the zones of interest, two general approaches to sample preparation have been used. 

These results were confirmed by an electron microscopy study using a freeze-etching replication technique (1 ). The aim of this technique was to conserve the real gel structure by blocking any diffusion processes in the gel sample by the freezing action of liquid nitrogen. The three-dimensional network is then recovered... 

Fig. 8 Freeze fracture replication technique for transmission electron microscopy (TEM). (From RefJ l)...

Polymer materials find a wide application in replication technologies for producing structures with submicron elements of intricate shapes and for nano-scale surface replication [1-4]. They show considerable promise for smoothing out the surface roughness to obtain good-quality inexpensive substrates used in fabrication of X-ray optic components [5,6], In this work, the features of silicon wafer surface replication by polymers were studied by atomic-force microscopy (AFM) and X-ray reflectometry (XRR) with a view to applying this replication technique to produce smooth polymer-glass combination substrates to be used in multilayer X-ray mirrors. 

This paper describes a systematic study by electron microscopy of adsorbed monolayers of long-chain fatty acids ranging from C14 to C26 Improvements in replication techniques and the electron microscopes themselves since the time of Epstein s original work, as well as the successful applications of electron microscopy cited above, gave reason to believe that such an investigation would be a useful supplement to the previous experiments of Bigelow and Brockway in elucidating the structure of the adsorbed films. 

Figure 3.3. Electron micrograph (replica) of a graft-type high-impact polystyrene with polybutadiene as the rubbery component (Keskkula and Traylor, 1967). In the absence of agitation, phase inversion does not occur, and an interwoven cellular structure results, with polybutadiene remaining as the continuous phase. The specimen was prepared for electron microscopy by exposing a polished surface to isopropanol vapor, which preferentially swells the polystyrene phase a double replication technique was then used. The reader should compare the results obtained by this technique to results obtained using thin-section transmission techniques (see, for example. Figure 3.2).

So far the evidences to suggest that TCs contain cellulose synthases were all indirect. In many cases, rosette TCs can not be visualized easily by freeze fracture replication technique even during stages of active cellulose biosynthesis in some plant cells. Therefore, we had to await for advances in immimocjTo-chemical techniques coupled with freeze-fracture electron microscopy to demonstrate directly that rosette TCs contain the catalytic subunit of cellulose synthase and the linear TCs in A. xylinum contain the c-di-GMP-binding protein that activates cellulose synthesis. 

Electron Microscopy can be used for resolution of smaller objects the practical limit of resolution being a few angstrom units. Electron Microscopy has been used in the study of the morphology of crystalline polymers. The usual techniques of replication, heavy-metal shadowing, and solvent etching are widely used. The direct observation of thin specimens, like polymer single crystals, is also possible and permits the observation of the electron-diffraction pattern of some specimen area, which is invaluable for... 

However to make things a whole lot more complicated, the two strands of the DNA molecule are antiparallel, yet only one site of replication is visible by low-resolution techniques, like electron microscopy during the repheation of double-stranded DNA, at what is known as the replication fork (Figure 3.30a). There is no way that DNA polymerase can synthesise one strand of DNA in the way which is illustrated in Figs 3.28/3.29 and simultaneously synthesise the other strand in the opposite direction, (which logically would have a 5 -phosphate at its... 

In a typical treatment of polyethylene, 1-2 pm is removed from the surface, with the reagent attacking preferentially the non-crystalline material. The surface can then be studied either by two-stage replication or by high-resolution scanning electron microscopy (SEM). The latter gives somewhat lower resolution than TEM, but is much easier to use than the production of replicas. In this technique scattered or secondary electrons emitted from the surface are collected as an electron beam is scanned across it in a raster like that used to produce a television picture and the image is built up in a similar way from the intensity detected. 

General corrosion control, prevention, and monitoring should be planned for from the onset. To detect and monitor corrosion, various methods must be used, while corrosion protection would be done by the addition of inhibition and use of protection coatings [5]. Visual examination, laser methods, the replication microscopy liquid penetration testing method, magnetic particles testing, the eddy current inspection method, acoustic emission technique, thermal methods of inspection, and nondestructive methods are the various methods to be adopted when monitoring pipeline corrosion [5]. 

Electron microscopy is a powerful direct experimental technique. Using electron microscopy information can be obtained on the presence of inhomogeneities, and on their shapes, sizes, size dispersion and number density. The experimental and theoretical aspects of this technique have been reviewed by Hirsh a/. (1965). There are two methods of observation. In the first, the topography of the sample surface is replicated and it is this replica, and not the sample which is then examined in the electron microscope. Generally carbon is used as the replicating material and shadowing at an angle with heavy elements (Pt) is used to accentuate the surface reUef. The resolution limit is about 50 A due to a microstructure in the rephca. As the sample itself is not examined, a diffraction pattern is not obtained. The sample surface can be either etched or unetched. An unetched surface wiU reveal cracks, voids, and polyphase microstructures if the various phases... 

A technique was developed to observe the lamellar morphology directly with transmission electron microscopy without the need of replication. The technique is a modification of the staining method by Trent [225], The lamellar thickness in these sections was 190 A. 

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