Orientational defects formation

The observation that the most photochemically reactive surface orientations all contain 101 facets suggests that the enhanced reactivity is not associated specificially with the bulk crystal orientation, but is a property of this particular surface plane. It is likely that there are special atomic configurations on this plane that either alter the efficiency with which photogenerated carriers are trapped at the surface or the rate at which they are transferred across the solid-liquid interface. Based on bulk geometry alone, there is nothing that sets the 101 plane apart from less reactive surfaces. On this surface, Ti cations are coordinated by five O, as they are on the (100) surface (which is inert). In the absence of higher resolution microscopy results, it is not possible to say if special molecular configurations are created by reconstruction or defect formation. 

Fig. 7.3. (a) Formation of an orientational defect pair, v and L, by an oblique proton jump or, equivalently, by rotation of a water molecule by znis about one of its bonds. (6) Separation of these two orientational defects by further oblique proton jumps. 

The effects of convection during the photodeposition of poly(diacetylene) thin films has been studied at Msushall Space Flight Center (26,27), The investigators found that defect formation was related to the intensity of convection and that double-difftisive convection and defects were found in all orientations of the experiment including illumination from above. 

Thin-film XRD is important in many technological applications, because of its abilities to accurately determine strains and to uniquely identify the presence and composition of phases. In semiconduaor and optical materials applications, XRD is used to measure the strain state, orientation, and defects in epitaxial thin films, which affect the film s electronic and optical properties. For magnetic thin films, it is used to identify phases and to determine preferred orientations, since these can determine magnetic properties. In metallurgical applications, it is used to determine strains in surfiice layers and thin films, which influence their mechanical properties. For packaging materials, XRD can be used to investigate diffusion and phase formation at interfaces... 

In Pins - embryos the initiation steps of apical complex formation occur normally. However, this complex cannot be maintained in mitotic neuroblasts. Hence, the importance of the maintenance of this complex for asymmetric cell division can be ascertained by assessing how Pins- neural progenitors divide. Pins- embryos exhibit all of the defects seen in insc mutants. Mitotic spindle orientation is defective. In the cells of mitotic domain 9 the 90° reorientation, which normally occurs in wild-type resulting in the orientation of the spindle along the apical—basal axis (Fig. 3A), fails to occur in the mutant (Fig. 3B). Mitotic spindle orientation of neuroblasts in the segmented CNS, deduced from DNA staining, also often fails to... 

There are a number of possible explanations for the formation of more than one photodimer. First, due care is not always taken to ensure that the solid sample that is irradiated is crystallographically pure. Indeed, it is not at all simple to establish that all the crystals of the sample that will be exposed to light are of the same structure as the single crystal that was used for analysis of structure. A further possible cause is that there are two or more symmetry-independent molecules in the asymmetric unit then each will have a different environment and can, in principle, have contacts with neighbors that are suited to formation of different, topochemical, photodimers. This is illustrated by 61, which contrasts with monomers 62 to 65, which pack with only one molecule per asymmetric unit. Similarly, in monomers containing more than one olefinic bond there may be two or more intermolecular contacts that can lead to different, topochemical, dimers. Finally, any disorder in the crystal, for example due to defective structure or molecular-orientational disorder, can lead to formation of nontopochemical products in addition to the topochemical ones formed in the ordered phase. This would be true, too, in those cases where there is reaction in the liquid phase formed, for example, by local melting. 

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