Microscopes image formation

C.E. Hall. Scattering phenomena in electron microscope image formation. J. Appl. Phys. 22, 5, 655-662 (1951). 

Run-of-the-mill instruments can achieve a resolution of 5-10 nm, while the best reach 1 nm. The remarkable depth of focus derives from the fact that a very small numerical aperture is used, and yet this feature does not spoil the resolution, which is not limited by dilfraction as it is in an optical microscope but rather by various forms of aberration. Scanning electron microscopes can undertake compositional analysis (but with much less accuracy than the instruments treated in the next section) and there is also a way of arranging image formation that allows atomic-number contrast, so that elements of different atomic number show up in various degrees of brightness on the image of a polished surface. 

However, going from the former qualitative analysis to a more quantitative one is much more troublesome, as the correct and quantitative interpretation of the results should carefully take into account all the steps into which the process of image formation in the electron microscope is divided. 

Harper JD, Lieber CM, Lansbury PT Jr. Atomic force microscopic imaging of seeded fibril formation and fibril branching by the Alzheimer s disease amyloid-beta protein. Chem Biol 1997 4 951-959. 

Kohl, H. and Rose, H. (1985) Theory of image formation by inelastically scattered electrons in the electron microscope. In Adv. Electronics and Electron Physics, Hawkes, P.W. (Ed.), Vol. 65, Academic Press, New York, pp. 173-227. 

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. 

Image formation in a transmission electron microscope can be considered as a two-step process. In the first step, the electron beam is interacting with the specimen. This interaction is very strong compared to X-ray or neutron scattering and causes multiple scattering events. In order to understand this process, the classical particle description of the electron is not adequate, and the quantum mechanical wave formalism has to be used. Thus, assuming the... 

Figure 1. (a) Image formation in an electron microscope Ro - undiffracted beam O -objective aperture A as placed in (a) (b) Contrast transfer function of JEOL JEM 2010 200 kV electron microscope Scherzer underfocus 8 = -43.4 nm, a = 0.6 mrad, g = 5 nm ... 

The microscopic image shows a juxtaposition of differently orientated areas whose sizes, varying between a few microns and several tens of microns, are associated particularly with the elementary composition of the initial carbonaceous material (4, 18, 19). The formation of a texture of this type, often called a mosaic structure, can be compared (20) to the crystallization of a supersaturated solution areas, each characterized by a definite orientation, develop from nuclei up to the total consumption of the isotropic material surrounding them. 

At high concentrations, the strands aggregate into large polymeric entities, initially via filament formation, followed by lateral, tree like growth. Figure 10.82a -c shows electron microscope images of the various mixtures under these conditions. Note, especially, the opposite handedness of the L- and D-triple helices (right- and left-handed helices, respectively). 

Figure 1.188 Microscope images of the color formation due to a reactive characterization of mixing in the five mixing elements of the recycle-flow micro mixer (Re = 28 150 pm). Phenolphthalein and NaOH solutions were mixed [56] (by courtesy ofTransducer Research Foundation).

Figure 10.3 Three examples of electron microscopic images showing different formation mechanisms of image contrast,...

Image formation is a crucial step in image analysis. Quantitative image analyzers consist of a high linearity television camera that can be interfaced with a microscope, macroviewer or videotape. An electron probe interface... 

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