Vertical line defects

Vertical line defects can be induced, for example, in samples with not perfect homeotropic anchoring (see Figure 6.2a). Lines parallel to Ihe film surfaces are usually present spontaneously in films with planar surface anchoring when the sample is cooled rapidly from the isotropic phase (see picture Figure 6.2b). 

Vertical and horizontal line defects in samples, (a) ScHieren texture of a 70-pm sample of MBBA (N-(p-methoxy-benzylidene)-p-n-butylaniline) at 20°C in homeotropic anchoring. To induce the vertical line defects an electric field of 6 Vrms 300 Hz applied vertically, (b) Horizontal line defects appeared spontaneously in planar ceU on cooling from the isotropic phase. The subsequent photos illustrate the evolution of a string network in a liquid crystal. The four snapshots have the same size, but were obtained at different times. Notice the progressive dilution of the string network (picture from http //tvww.damtp.cam.ac.uk/user/gr/public/cs phase.html). Bar 100 pm. 

Fig. 3.12. Micro-Raman spectra in the x(yy)x scattering configuration of several PLD-grown, element-doped wurtzite-structure (0001) ZnO thin films on (0001) sapphire [43,48]. Defect-induced modes are marked by solid vertical lines. The asterisks indicate modes, which seem to occur for specific dopant species only. Excitation with Ar+-laser line A = 514.5 nm and laser power P < 40 mW...

Figure 11.6. Schematic illustrations of brittle fracture, (a) Idealized limiting case of perfectly uniaxially oriented polymer chains (horizontal lines), with a fracture surface (thick vertical line) resulting from the scission of the chain backbone bonds crossing these chains and perpendicular to them. This limit is approached, but not reached, in fracture transverse to the direction of orientation of highly oriented fibers, (b) Isotropic amorphous polymer with a typical random coil type of chain structure. Much fewer bonds cross the fracture surface (thick vertical line), and therefore much fewer bonds have to break, than for the brittle fracture of a polymer whose chains are perfectly aligned and perpendicular to the fracture surface, (c) Illustration of a defect, such as a tiny dust particle (shown as a filled circle), incorporated into the specimen during fabrication, which can act as a stress concentrator facilitating brittle fracture.

Another example is formation of boodjooms at the cell surfaces. Now we are interested not in the linear disclinations responsible for the SchUeren texture but in their nuclei at the solid substrates limiting a liquid crystal cell. The linear discUna-tions of strength s = 1 may annihilate within the bulk due to some reconstruction of the director field induced, for instance, by temperature or a flow of the material. For example, a bulk discUnation of strength s = +1 shown by the solid vertical line in Fig. 8.18b disappears but its nuclei localized at the surfaces transform into new, surface defects. Fig. 8.18c illustrates the situation at one of the two surfaces. The escaped line leaves behind it a boodjoom. We meet such a situation in thick planar cells where the Schlieren textures with four brushes are observed. 

Fig. 8.20 Volterra process. A stack of the cholesteric quasi-layers with vertical helical axis and a cut S shown by the solid line terminated in point L (a). The cut is open up-down and the cholesteric material is added on the right of the cut (b). The final structure of the quasi-layers after relaxation leaving a line defect (c)...

Figure 4. Number of gauche defects formed as a function of simulation time when a flexible and a rigid single-wall nanotube are used to indent (and extracted from) a Cjs monolayer. Vertical lines represent the time when tip motion is reversed.

The polarizing optical texture and the corresponding director structures in a capillary with homeotropic boundary conditions are illustrated in Figure 6.4. Note that the disclination line in the middle along the capillary axis is due to the escape to the third direction. The vertical lines indicate regions where the different escape directions meet. And the crosses are point defects. 

Figure 10.18 Schematic diagrams of the pendeo-epitaxial layers. Vertical lines indicate defects in the seed area propagating to the sample surface.

Bending contours are due to bending of thin TEM sample. Note some defects (mainly stacking faults) present in the Ga-wing (vertical lines). 

It can be observed from the Figure 1 that the sensitivity of I.I. system is quite low at lower thicknesses and improves as the thicknesses increase. Further the sensitivity is low in case of as observed images compared to processed images. This can be attributed to the quantum fluctuations in the number of photons received and also to the electronic and screen noise. Integration of the images reduces this noise by a factor of N where N is the number of frames. Another observation of interest from the experiment was that if the orientation of the wires was horizontal there was a decrease in the observed sensitivity. It can be observed from the contrast response curves that the response for defect detection is better in magnified modes compared to normal mode of the II tube. Further, it can be observed that the vertical resolution is better compared to horizontal which is in line with prediction by the sensitivity curves. 

Figure 3. Electrostatic potential map for the two bare defects and identification of the position of the atoms of the dissociated H2 molecule (H atoms in the Tfi configuration are in dark grey). The sections are in a vertical plane through the H atoms. Consecutive isopotential lines differ by 0.02 a.u. (0.54 V) continuous, dashed and dot-dashed curves refer to positive, negative, arid zero potential, respectively. Lines corresponding to absolute values larger than 0.3 a.u. are riot plotted.

Figure 3.12 shows typical Raman spectra of several doped ZnO thin films. Additional modes (AM), occurring at to 275, 510, 582, 643, and 856 cm-1 (the first four of them are shown and marked by vertical solid lines in Fig. 3.12), were first assigned to N-incorporation [49-51], because the intensity of these modes was reported to increase with increasing N-content [50], However, the AMs appear also in Raman spectra of ZnO samples doped with other elements (Fig. 3.12a), [48,52,53]). Therefore, it was suggested that the AMs are related to defect-induced modes [48]. Theoretical considerations confirmed this assignment [131]. It was discussed that the AMs could be related to modes of ZnO, which are Raman-inactive within a perfect crystal. Upon doping-induced defect formation, the translational crystal symmetry can be broken, and Raman-inactive modes may become Raman-active. The Raman spectra of the ZnO thin films with transition metals in Fig. 3.12b show a different behavior than those in Fig. 3.12a [43,48], Raman spectra of Fe0.08Zn0.92O contain the above described AMs, but with different intensity ratios. For MnZnO, CoZnO, and NiZnO a broad band between iv 500 cm-1...

A Lorentzian-like line shape indicates random defect distribution across the surface. The oscillation of the rocking curve width as a function of Lri is a direct result of constructive and destructive interference conditions that are alternately satisfied as the momentum transfer perpendicular to the surface, Qz, increases. The vertical extent of the defects, h, is revealed through the relation h = 27dbQz = Chid/5L where 8Q is the characteristic period of the oscillations. The periods of oscillations in Figures 26C and 26D are 80 = 2 / for both surfaces, implying that for each surface the predominant defects correspond to unit-cell-high steps, with h = 7.2 A and 3.4 A on the (001) and... 

Fig. 11 Passivating effect of a phosphate layer. Distribution of vertical component of current over a scratched phosphated galvanized steel surface measured by the SVET method. The scratch penetrates down to the steel surface. Cathodic zones (current < 0) are indicated by the filled areas, while anodic zones (current > 0) are transparent. Because of the passivating properties of the phosphate layer, the anodic reaction remains localized in the vicinity of the scratch defect. Each isocurrent line represents lOpAcm. Original data Irsid.

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