Resolution in TEM

The resolution in TEM is limited by lens aberrations. In contrast to optical microscopy, where by serially ordering concave and convex lenses, aberrations can be compensated and hence the wavelength of the radiation is resolution limiting in TEM lens aberrations cannot be compensated since concave electron lenses are not feasible. The objective lens is the crucial part for image defining the microscope s resolution. The quality of the objective lens is described by the constants of spherical Cs(" 0.5-3mm) and chromatic aberration Cc ( 1-2 mm). Recently, microscopes equipped with complex correctors for the spherical aberration have become available. ... 

The use of several techniques testing the magnetic response of particles ensembles on different time scales is desirable, especially when their size reaches the limit of resolution in TEM and their diffraction peaks are too broad for permitting the identification of all formed phases. The incorporation of Fe, Ni salts in TH permits to obtain metallic particles by ion irradiation or aimealing at low temperatures, simply in vacuum, while undesired phases are formed in TEOS (often even when heat treated in pure H2 atmosphere [9]). The formation of smaller particles, perfectly encapsulated in dense films of glass, under ion irradiation should permit to increase the areal density of information in magnetic memories. 

Disadvantages of STEM relate to image resolution, image quality and the cost of dedicated instruments. The loss of resolution and image contrast compared to TEM must be considered for each application as the images tend to be softer in STEM. The better resolution in TEM also is a major factor in imaging if the structures of interest require ultimate resolution. On the other hand, there are specimens which cannot be... 

Application High-resolution signal (TEM, STEM) Back-scattering of electrons (BSE signal in SEM) Analytical signal (TEM, STEM, SEM) Emission of secondary electrons (SE signal in SEM)... 

Light element spectroscopy for concentration, electronic, and chemical structure analysis at ultra-high lateral resolution in a TEM or STEM... 

The HRTEM technique has become popular in recent years due to the more common availability of high-volti e TEMs with spatial resolutions in excess of... 

Recent demands for polymeric materials request them to be multifunctional and high performance. Therefore, the research and development of composite materials have become more important because single-polymeric materials can never satisfy such requests. Especially, nanocomposite materials where nanoscale fillers are incorporated with polymeric materials draw much more attention, which accelerates the development of evaluation techniques that have nanometer-scale resolution." To date, transmission electron microscopy (TEM) has been widely used for this purpose, while the technique never catches mechanical information of such materials in general. The realization of much-higher-performance materials requires the evaluation technique that enables us to investigate morphological and mechanical properties at the same time. AFM must be an appropriate candidate because it has almost comparable resolution with TEM. Furthermore, mechanical properties can be readily obtained by AFM due to the fact that the sharp probe tip attached to soft cantilever directly touches the surface of materials in question. Therefore, many of polymer researchers have started to use this novel technique." In this section, we introduce the results using the method described in Section 21.3.3 on CB-reinforced NR. 

Dedicated SEM instruments have a resolution of about 5 nm. The main difference between SEM and TEM is that SEM sees contrast due to the topology and composition of a surface, whereas the electron beam in TEM projects all information on the mass it encounters in a two-dimensional image, which, however, is of subnanometer resolution. 

The development of X-ray microanalysis in the TEM has been driven by the improvement in spatial resolution in comparison with EPMA. This arises because thin specimens are used, so less electron scatter occurs as the beam traverses the specimen, and also because of the higher electron energy in the TEM also reduces scatter. The disadvantage is that the specimen has to be prepared in the form of a thin foil, and the problems involved in this process have already been discussed. 

The ideal solution to microanalysis would be simply to freeze the plant material rapidly to the temperature of liquid nitrogen and then section it while it is still frozen on a cryotome. The frozen sections would then be transferred to a cold stage in a TEM and analyzed. In theory, no ion movement will take place and analysis at the high resolution of TEM should be possible. Indeed, this is a useful technique for liver, kidney, and soft animal tissues, but unfortunately it is almost impossible to cut tough plant material, and maintain the sections in a reasonable state for analysis (2). Even if this problem could be overcome unstained tissues will be difficult to visualize in TEM. 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

On the other hand, electron diffraction is much more sensitive than X-Ray as interaction as is many thousands times stronger in comparison. Again, in TEM, ED patterns can be obtained instantly with sufficient quality better than 0.1 nm resolution. 

In solid state physics, the sensitivity of the EELS spectrum to the density of unoccupied states, reflected in the near-edge fine structure, makes it possible to study bonding, local coordination and local electronic properties of materials. One recent trend in ATEM is to compare ELNES data quantitatively with the results of band structure calculations. Furthermore, the ELNES data can directly be compared to X-ray absorption near edge structures (XANES) or to data obtained with other spectroscopic techniques. However, TEM offers by far the highest spatial resolution in the study of the densities of states (DOS). 

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