Amplitude contrast

Figure Bl.17.4. Visualization of image contrast fomiation methods (a) scattering contrast and (b) interference contrast (weak phase/weak amplitude contrast).

Figure Bl.17.5. Examples of CTFs for a typical TEM (spherical aberration = 2.7 mm, 120 keV electron energy). In (a) and (b) the idealistic case of no signal decreasing envelope fimctions [77] are shown, (a) Pure phase contrast object, i.e. no amplitude contrast two different defocus values are shown (Scherzer focus of 120 mn imderfocus (solid curve), 500 mn underfocus (dashed curve)) (b) pure amplitude object (Scherzer focus of 120 mn underfocus) (c) realistic case mcluding envelope fimctions and a mixed weak...

For a detailed discussion on the analytical teclmiques exploiting the amplitude contrast of melastic images in ESI and image-EELS, see chapter B1.6 of this encyclopedia. One more recent but also very important aspect is the quantitative measurement of atomic concentrations in the sample. The work of Somlyo and colleagues [56]. Leapman and coworkers and Door and Gangler [59] introduce techniques to convert measured... 

Based on TEM studies of supported metal catalysts, several workers have concluded that their catalysts were made of two-dimensional discs or rafts , where virtually all atoms are at the particle surface. However, sample tilting experiments in TEM have shown that great care should be exercised in the interpretation of TEM images of small particles (<2 nm in size), since phase contrast effects may dominate and variations in the particle contrast with specimen orientation can occur as a result of amplitude contrast effects (Treacy and Howie 1980). Sample tilting is therefore necessary to ensure correct interpretations of TEM images of metal-particle catalysts. This will be discussed further in the following sections. 

Nikoonahad, M. (1987). Differential amplitude contrast in acoustic microscopy. Appl. Phys. Lett. 51, 1687-9. [69]... 

Nikoonahad, M. and Liu, D. C. (1990). Pulse-echo single frequency acoustic nonlinearity parameter (B/A) measurement. IEEE Trans. UFFC 37, 127-34. [43, 181] Nikoonahad, M. and Sivers, E. A. (1989). Dual beam differential amplitude contrast scanning acoustic microscopy. In Acoustical imaging, Vol. 17 (ed. H. Shimizu, N. Chubachi, and J. Kushibiki), pp. 17-25. Plenum Press, New York. [69]... 

In electron microscopy as in any field of optics the overall contrast is due to differential absorption of photons or particles (amplitude contrast) or diffraction phenomena (phase contrast). The method provides identification of phases and structural information on crystals, direct images of surfaces and elemental composition and distribution (see Section H below). Routine applications, however, may be hampered by complexities of image interpretation and by constraints on the type and preparation of specimens and on the environment within the microscope. 

Several studies have looked at schizophrenia spectrum disorders and results have been less clear than for first-degree relatives. For instance, coherent motion thresholds, PI amplitude, contrast sensitivity, and form and trajectory discrimination were not impaired (Farmer et al., 2000 O Donnell et al., 2006 Vohs et al., 2008) in schizotypal personality disorder. However, a backward masking deficit was found in schizotypal personality disorder (Cadenhead et al., 1999). 

Such is not the case if, instead of the axial detector, we employ the annular dark-field detector for which P la 1, where P is the effective angle subtended by the detector. Under these circumstances we anticipate that phase contrast will not contribute significantly to the image. Instead, modulation of the amplitude-contrast transfer function should be noted in an image if, for example, a probe of FWHM comparable to atomic separations is scanned across a sharp edge or a periodic structure. This is observed in Figure 8, in which a probe of FWHM 3 A is scanned across... 

Figure 8 Annular dark-field lattice image of graphite crystallite, showing amplitude contrast. Fringe separation 3.4 A...

Amplitude contrast can arise from discontinuities in refractive index. 

Diffraction and mass-thickness contrast are both caused by an intensity change of a diffracted beam over the field of view. Since the intensity, specifically the amplitude, of a beam causes these types of image contrast, diffraction and mass-thickness contrast are referred to as amplitude contrast. ... 

Although this concrete explanation of the amplitude contrast is appropriate for a basic understanding, it does not account for all image features. It is based on the kinematical approach to explain electron diffraction. In the kinematical approach, an electron can be scattered once and once it is scattered it will not change its momentum. For very thin samples of light elements, this approximation is sometimes justifiable. 

Microscopy with differential interference optics (e.g., Zeiss-Nomarski amplitude-contrast optics Webster et al., 1974). 

Toyoshima C, Yonekura Kand Sasabe H 1993 Contrast transfer for frozen-hydrated specimens II. Amplitude contrast at very low frequencies. Ultramicroscopy 48 165-76... 

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