Topographic contrast

The topographic contrast of the islands disappears above 80% RFl [72], and no islands can be observed after tip contact at this and higher humidity. These observations can be explained by assuming that the metastable islands formed by capillary condensation correspond to a second or higher layer of water above the first one (phase-I). As we shah see... 

The disordered arrangement of the globuh and worm-hke species in combination with their uniform shape and diameter of 50 A demonstrates that the intramolecular self-assembly did not depend on intermolecular ordering. For both types of particles, the monolayer thickness was similar to the lateral diameter of the particles d = 50 5A. The topographic contrast of the images in Fig. 6 was enabled by strong molecular segregation and weak interpenetration of the particles. 

There is one picture in which plastic deformation seems undoubtedly to have been captured (Ishikawa et al. 1989). Figure 11.13 shows a specimen of an Fe-3%Si alloy that has been deformed. Every precaution was taken to eliminate spurious sources of contrast for example, the specimen was carefully repolished after deformation to avoid any topographical contrast due to bowing in or out of the surface around a stress concentrator as a result of deformation under plane stress. So the contrast seems indubitably to be due to interaction of Rayleigh waves with regions of plastic deformation. 

Its morphology and texture are described by the secondary electron images (topographical contrast). 

A-B subtracting the signals enables topographical contrast to be enhanced and chemical contrast to be eliminated. 

Secondary electron images have topographical contrast. They are of little value in electron microprobe analysis because the WDS spectrometer used for analysis requires working on perfectly flat (polished) samples. Their only use is in identifying holes, areas which should be avoided during analysis. 

Fig. 3 shows SFM image of one of the sections (thickness of - 100 nm) of K562 cell embedded in epoxy resin. It should be noticed that topographical contrast and the identification of the K562 internal ultrastructure critically depend on the procedure of cell preparation before embedding (chemical fixation or high-pressure freezing and freeze-substitution). 

Fig. 9. STM image (10x4 nm, V.j. = -2.2mV, /.j. = 0.5nA) of the NiAl(l 10) surface annealed at 700°C. Only one type of atom is visible as protrusion with a corrugation of 20 - 25 pm. As ab initio calculations show [51], this species is Al. The experimental corrugation coincides with the buckling found by LEED (Al atoms are geometrically 22 pm higher [48]) and is therefore explained as topographic contrast.

Figure 4.11 Generation of topographic contrast (a) the trajectory effect, which arises from the orientation of surface with respect to the detector in an SEM, is similar to (b) reflected light effects from the orientation of surface with respect to the light source in a light microscope. (Reproduced with kind permission of Springer Science and Business Media from J.I. Goldstein et al, Scanning Electron Microscopy and X-ray Microanalysis, 2nd ed., Plenum Press, New York. 1992 Springer Science.)...

Nevertheless, topographic contrast in an SEM is not exactly the same as the contrast achieved by inclined light illumination. In an SEM image, the electron number effect will create bright areas in the image that do not correspond to surface contours on the specimen. Figure 4.13 illustrates the electron number effect. When the electron probe hits a surface at an angle, more... 

Figure 4.19 Comparison of the effect of acceleration voltage on topographic contrast of acid etched titanium specimen, (a) 20 kV, and (b) 5 kV.

Subsurface structures in silicon were also studied using apertureless s-SNOM in the IR range. Lahrech et al. have shown successfully that implanted boron lines in silicon can be detected with a lateral resolution of -400 mn, even in the absence of any topographical contrast [47]. Knoll and Keilmann have performed near-field... 

In this part the electronic properties of chemisorbed hydrogen on Gd(OOOl) will be discussed. For the photoemission investigation, smooth Gd(OOOl) films were prepared and subsequently exposed to hydrogen. It was already shown in Sect. 3.1 (Chap. 3) that the Gd smface state exists both on smooth films and multilayer Gd islands. Therefore, multilayer island films were chosen for the STM investigations to provide topographical contrast in order to distinguish between sample states and tip induced artifacts as well as to determine the influence of different island heights. The detailed preparation procedure was already described in Sect. 3.1 (Chap. 3). 

In this imaging mode, only surface features can be seen by topographic contrast. In the transmitted electron mode, most of the sample was too thick to pass electrons, and spheres were difficult to distinguish. In the Pittsburgh No. 8 sample, 400 C is the onset of fluidity, and mesophase spheres were sufficiently abundant to be observed in the STEM (Figure 4). 

Topographical features of the sample produce distortions in the image and this effect can be used to provide additional topographical contrast. 

Secondary electron mode real time magnified topographic contrast images. Back-scattering mode real time magnified elemental contrast images. 

Quantum dots are detectable by SEM by topographical contrast with secondary electron imaging (SEI), compositional contrast with backscattered electron imaging (BEI), and scanning transmission electron imaging. By SEI, the quantum dots appear as particles on exposed surfaces that can resemble normal biological structures. However, the CdSe core and ZnS coating impart... 

The SE is attracted to the detector using a positively biased collector grid placed on one side of the specimen. The topographic contrast depends mainly on the incident angle and the border effect (Fig. 2). 

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