Imaging, in electron microscopy

The high heavy atom content of metal clusters makes them attractive candidates for imaging in electron microscopy, for X-ray contrast agents, or for determining the phasing in the crystallography of biological molecules. 

Liang, L. and Li, Z.R. (2003). Digital imaging in electron microscopy. In Li, Z.R. (Ed.) Industrial Applications of Electron Microscopy, New York Marcel Dekker. WOSH. NIOSH manual ofanalytical methods (4th). ONLINE. (1994). U.S. Division of Health and Human Services National Institute of Occupational Safety and Health. Available http //www.cdc.gov/niosh/nmam/. 

Apart from the sheer complexity of the static stmctures of biomolecules, they are also rather labile. On the one hand this means that especial consideration must be given to the fact (for example in electron microscopy) that samples have to be dried, possibly stained, and then measured in high vacuum, which may introduce artifacts into the observed images [5]. On the other, apart from the vexing question of whether a protein in a crystal has the same stmcture as one freely diffusing in solution, the static stmcture resulting from an x-ray diffraction experiment gives few clues to the molecular motions on which operation of an enzyme depends [6]. 

Figure 6.3(b) is a good example of the beautifully sharp and clear images of dislocations in assemblies which are constantly being published nowadays. It is printed next to the portrait of Peter Hirsch to symbolise his crucial contribution to modern metallography. It was made in Australia, a country which has achieved an enviable record in electron microscopy. 

The other striking feature of nanotubes is their extreme stiffness and mechanical strength. Such tubes can be bent to small radii and eventually buckled into extreme shapes which in any other material would be irreversible, but here are still in the elastic domain. This phenomenon has been both imaged by electron microscopy and simulated by molecular dynamics by lijima et al. (1996). Brittle and ductile behaviour of nanotubes in tension is examined by simulation (because of the impossibility of testing directly) by Nardelli et al. (1998). Hopes of exploiting the remarkable strength of nanotubes may be defeated by the difficulty of joining them to each other and to any other material. 

At present only low resolution (>30A) structures, all derived from single particle analysis of images from electron microscopy, are available for the entire DP3R. These structures differ in their details, but all show a roughly square structure with fourfold symmetry and lateral dimensions of about 20 nm (Fig. 2). 

TEG structure refinement has distinctly observed in electron microscopy studies of the oxidized TEG powders subjected to the repeated thermal shock. In this case the size of TEG macropores was equal to 1.5-2 pm that is essentially lower that for source TEG. Figure 2 presents SEM images of the source TEG particle (a) and TEG particle oxidized by sulfuric acid and re-exfoliated at 800°C (b). 

Secondary electrons are very low energy electrons (less than 50 eV) knocked out of the loosely bound outer electronic orbitals of surface atoms. Because of their low energy, they can only escape from atoms in the top few atomic layers and are very sensitive to surface topography - protruding surface features are more likely to produce secondary electrons which can escape and be detected than are depressed features. The intensity of secondary electrons across the sample surface therefore accurately reflects the topography and is the basis of the image formation process in electron microscopy. 

XD Zou. On the phase problem in electron microscopy the relationship between structure factors, exit waves, and HREM images. Microsc. Res. Tech. 46 202-219,... 

D reconstruction can be performed by restoring the 3D Fourier space of the object from a series of 2D Fourier transforms of the projections. Then the 3D object can be reconstructed by inverse Fourier transformation of the 3D Fourier space. For crystalline objects, the Fourier transforms are discrete spots, i.e. reflections. In electron microscopy, the Fourier transform of the projection of the 3D electrostatic potential distribution inside a crystal, or crystal structure factors, can be obtained from HREM images of thin crystals. So one can obtain the 3D electrostatic potential distribution (p(r) inside a crystal from a series of projections by... 

Saxton, W.O. Computer Techniques for Image Processing in Electron Microscopy. Advances in Electronics and Electron Physics. Supplement 10, Academic Press, New York (1978). 

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

Image analysis may be applied to gold labeling in electron microscopy in order to achieve improved localization and facilitate quantitative analysis of the gold particles (24). 

Yada, R.Y., Harauz, G., Marcone, M.F., Beniac, D.R., and Ottensmeyer, F.P. 1995. Visions in the mist The Zeitgeist of food protein imaging by electron microscopy. Trends Food Sci. Technol. 6, 265-270. 

In the natural world, numerous knotted and entwined forms of DNA strands are known and have been imaged by electron microscopy (Figure 10.86)." Knotted proteins such as lactoferrin and ascorbinic acid... 

A limiting factor in electron microscopy is the quality of the electron beam. Aberrations introduced by the optics limit both spatial resolution and analytical capabilities. There is a need to correct for the spherical and chromatic aberrations introduced by the electron optics. This will result in improved coherence of the beam and improved imaging and diffraction. In particular, these advances will permit the analysis of amorphous samples. Smaller beam sizes can also be achieved, allowing for sub-Angstrom resolution chemical analysis of samples. Development of higher-quality electron beams and short pulses of electron beams would broaden and deepen the application of electron microscopy. 

Radermacher M, Ruiz T. (2006) Three-dimensional reconstruction of single particles in electron microscopy image processing. Methods Mol. Biol. 319, 427-61. 

In electron microscopy a sample is bombarded with a finely focused beam of monochromatic electrons. Products of the interaction of the incident electron beam with the sample are detected. If the sample is sufficiently thin—up to 200 nm thickness—the beam is transmitted after interacting with the sample, leading to the technique of transmission electron microscopy (TEM). TEM is used to probe the existence of defects in crystals and phase distributions. Scanning TEM instruments have been recently developed to obtain images over a wider area and to minimize sample degradation from the high-intensity beams. 

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