Misorientation

What gives rise to streaks in a RHEED pattern from a real surface For integral-order beams, die explanation is atomic steps. Atomic steps will be present on nearly all crystalline surfaces. At the very least a step density sufficient to account for any misorientation of the sample from perfeedy flat must be included. Diffraction is sensitive to atomic steps. They will show up in the RHEED pattern as streaking or as splitdng of the diffracted beam at certain diffraction conditions that depend on the path difference of a wave scattered from atomic planes displaced by an atomic step height. If the path difference is an odd muldple of A./2, the waves scattered... 

The PIFs increased the likelihood of the strong stereotype takeover in the case study were the fact that the worker was more used to operating the valve for reactor B than reactor A, together with the distracting environment. In addition, the panel was badly designed ergonomically, and valves A and B were poorly labeled and quite close physically. On the basis of the evaluation of the PIFs in the situation, the internal error mechanisms could be stereotype takeover or spatial misorientation. 

There apparently exists a critical amount of liquid phase for the optimization of grain/interface boundary sliding during superplastic deformation. The optimum amount of liquid phase may depend upon the precise material composition and the precise nature of a grain boundary or interface, such as local chemistry (which determines the chemical interactions between atoms in the liquid phase and atoms in its neighboring grains) and misorientation. The existence of an equilibrium thickness of intergranular liquid phase in ceramics has been discussed [14]. This area of detailed study in metal alloys has not been addressed. 

This property is readily established from the definition of Fourier transform and convolution. In scattering theory this theorem is the basis of methods for the separation of (particle) size from distortions (Stokes [27], Warren-Averbach [28,29] lattice distortion, Ruland [30-34] misorientation of anisotropic structural entities) of the scattering pattern. 

Unless the ubiquitous misorientation of crystals in polycrystalline materials has been eliminated by some other method (cf. Chap. 9)... 

To demonstrate the effect of misorientation or even isotropization let us consider a structural entity52 which is a perfect lamellar stack. Figure 8.12 demonstrates... 

Equation (8.59) defines the ID interference function of a layer stack material. G (s) is one-dimensional, because p has been chosen in such a way that it extinguishes the decay of the Porod law. Its application is restricted to a layer system, because misorientation has been extinguished by Lorentz correction. If the intensity were isotropic but the scattering entities were no layer stacks, one would first project the isotropic intensity on a line and then proceed with a Porod analysis based on p = 2. For the computation of multidimensional anisotropic interference functions one would choose p = 2 in any case, and misorientation would be kept in the state as it is found. If one did not intend to keep the state of misorientation, one would first desmear the anisotropic scattering data from the orientation distribution of the scattering entities (Sect. 9.7). 

Figure 9.2. Reflection 4m (s) smeared by misorientation of the ensemble of crystallites (structural entities). The center of gravity is found at s/jd- Definitions of polar coordinates Dashed lines indicate the radial direction of the integration that leads to a projection onto the orientation sphere resulting in the pole figure g kl ([Pg.208]

If the observed reflections are not on spherical arcs, the computation of an orientation parameter becomes an arbitrary operation that is not exclusively related to misorientation of structure. Most probably the topology of the structural entities is coupled to their orientation6, and Chap. 10 applies. 

History. Wilke [129] considers the case that different orders of a reflection are observed and that the orientation distribution can be analytically described by a Gaussian on the orientation sphere. He shows how the apparent increase of the integral breadth with the order of the reflection can be used to separate misorientation effects from size effects. Ruland [30-34] generalizes this concept. He considers various analytical orientation distribution functions [9,84,124] and deduces that the method can be used if only a single reflection is sufficiently extended in radial direction, as is frequently the case with the streak-shaped reflections of the anisotropic... 

Figure 9.6. Fanning-out of an equatorial streak in a fiber pattern caused from misorienta-tion. Dashed arcs indicate azimuthal scans that are performed in practical measurements. The recorded scattering curves are used to separate the effects of misorientation and extension of the structural entities... 

Figure 9.7. Separation of misorientation (Bg) and extension of the structural entities (1/ (L)) for known breadth of the primary beam (Bp) according to Ruland s streak method. The perfect linearization of the observed azimuthal integral breadth measured as a function of arc radius, s, shows that the orientation distribution is approximated by a Lorentzian with an azimuthal breadth Bs... 

Low-angle tilt boundaries are the most easily visualized. Two regions of crystal separated by a slight misorientation can be drawn as a set of interlocking steps (Fig. 3.21a)- The edge dislocations coincide with the steps. The separate parts can be linked to make the edge dislocation array clearer (Fig. 3.21b). In the situation in which the misorientation between the two parts of the crystal is 0, the distance between the steps A and C is given by twice the dislocation separation, 2d, where... 

The pore growth direction is along the (100) direction and toward the source of holes. For the growth of perfect macropores perpendicular to the electrode surface (100), oriented Si substrates are required. Tilted pore arrays can be etched on substrates with a certain misorientation to the (100) plane. Misorientation, however, enhances the tendency to branching and angles of about 20° appear to be an upper limit for unbranched pores. For more details see Section 9.3. 

The normalized peak-shape function PS introduced by equation (1) must be determined in order to figure out the dependence of PS on several crystallite parameters, such as average size of crystallites, misorientation of crystallites in the sample etc. These parameters lead to a broadening of reflections, which must be taken into account. 

Misorientation can be an issue during the time of collection of ED patterns as sometimes this can exceed 60 min in accumulation mode, and d5mamical diffraction contribution is observed (we may anticipate its presence due to the appearence of forbidden kinematically reflections in the pattern like +- 002). However, is important to note that misorientation effects become less critical and intensity of such forbidden reflections is lowered after applying precession mode to the ED pattern. Similar results have also been observed by M.Gemmi with Si samples. 

Again, it is important to note that in data taken without precession mode light atoms like lithium and oxygen do not appear well generally.Small crystal misorientations due to time of measurement and dynamical diffraction contributions to many reflections in o precession mode may well explain such results. 

In this chapter we discuss the measurement and analysis of simple epitaxial stractures. After showing how to select the experimental conditions we show how to derive the basic layer parameters the composition of ternaries, mismatch of quaternaries, misorientation, layer thickness, tilt, relaxation, indications of strain, curvature and stress, and area homogeneity. We then discuss the hmitations of the simple interpretation. 

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