Transmission electron contrast modes

As a result of this, microtomed blends were studied under the transmission electron microscopy mode to provide a more accurate description of the microstructure in this compositional range. The thin sections were mildly doped (stained) with iodine to provide the requisite phase contrast and moderate conductivity to avoid charging effects. Figure 3 is a representation transmission electron micrograph obtained from such a specimen. 

Scanning Transmission Electron Microscopy (STEM) [22]. STEM represents a merger of the concepts of TEM and SEM. Modes of operation and mechanisms of contrast and of imaging are essentially the same as in CTEM but the main advantage of STEM is the ability to carry out microanalysis at very high resolution (see Section H). 

Film Preparation for Electron Microscopy. (SN), N P Cl, (NPCl ), DMDA, (DMDA), TCDU, and (TCDU) were all prepared for examination by use of a collodion stripping technique or by sub-strate dissolution, after Pt, C, or Au coating to enhance film strength and contrast. A Jeol JEM lOOB transmission electron microscope was used in both bright field and diffraction modes. 

Transmission electron microscopy (TEM) is also widely employed, in its simplest bright-field mode, as a tool for direct visualization of the nanocomposite structure of polymer nanocomposites. This is possible because there exists sufficient contrast for the transmitted electrons between the polymer matrix and most fillers (inorganic particles, carbon in nanotubes or graphite, and almost all oxides) without polymer staining. In the extreme case, high-resolution TEM can even provide a qualitative picture of the inorganic filler crystal structure, or can be... 

Unlike SEM, the inelastic scattered electrons, secondary electrons, for example, are not significant for image contrast in the TEM (if we disregard the imaging mode for STEM— scanning transmission electron microscopy ) and are excluded from analysis through the lens objective. 

For studying supported catalysts, TEM is the commonly applied form of electron microscopy, and today images as shown in Figure 7.1 are obtained routinely. In general, the detection of supported particles is possible provided that there is sufficient contrast between the particles and the support. This may impede applications of TEM on well-dispersed supported oxides [11]. Contrast in the transmission mode is caused not only by the attenuation of electrons due to density and thickness variations over the sample, but also by diffraction and interference. For example, a particle in a TEM image may show less contrast than other identical... 

There are two instruments that are used for electron imaging TEM and SEM. As the name implies, the transmission mode measures the intensity from an electron source after it has passed through a transparent sample (Figure 7.6a). In contrast, SEM features the scanning of an electron beam over selected regions of an opaque sample (Figure 7.6b). 

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