Cleavage Plane model

A second product is the ICE Solid-State Model Kit, developed by L. A. Mayer and G. C. Lisensky, which makes it possible to build extended three-dimensional structures Using a base with holes, templates for some 60 different structures, rods, and four sizes of spheres in radius ratios, common crystal structures can be assembled in a matter of minutes (3). Furthermore, many structures can be assembled from different perspectives by teams of students For example, the cubic NaCl unit cell can be assembled with its orientation on the face of the cube or on the body diagonal. Natural cleavage planes can be found with the kit Lifting one sphere will separate atomic planes from one another. (Contact ICE for ordering information.)... 

Figure2.1.50 Stereoscopic representation of the crystal packing of 64 b on (-102) showing layers separated by cleavage planes next to the sickle-shaped channels and a pair of the closely arranged molecules that photodimerize due to the migrational capability of the crystal the dimer interactions are indicated with long bonds in the dimer pair and in the crystal model.

The first step in building a planar model of a surface is cleaving the carefully-optimised bulk crystal to produce a slab with two exposed faces. Both surface orientation and cleavage plane must be selected. Low-index orientations hkt) are parallel to close-packed layers of ions and so can be expected to show little corrugation and minimal surface area. As a result, low-index orientations are often those of lowest surface energy and predominate in experiment. 

We used the cleavage plane of mica crystals as a model substrate in this work. Ruby mica is known to expose negative surface sites on file basal cleavage plane that are neutralized by ions in the bulk oystal. The remaining ions can dissociate in an aqueous environmwit and a double layer is formed in the vicinity of this negatively charged surface. The surface density of such ion sites (0.48 nm ) is determined by the oystal structure. 

Only the elastic stresses can relax without affecting the crystal structure. If the axial temperature gradient is constant, the flexure of the cleavage planes will disappear as the temperature smoothes out However, the temperature fields in the crystal are always of a more complex nature and the emergence of a free temperature bend, i.e. a constant axial temperature gradient, becomes possible only upon suppression of the radial heat curvature in the growing crystal. The models of formation of the cleavage-plane flexures are described in reference [22]. 

Because chalcopyrite does not have preferential cleavage plane, many different surfaces are exposed when the mineral is broken, increasing the difficulty to determine experimentally their properties. In fact, the previous study about the reconstruction of both terminations of the (001) surface was extended to other surfaces like (100), (111), (112), (101) and (110) providing general information about the chalcopyrite surfaces. Three reconstruction mechanisms arose from this investigation. Slab models were constructed to describe properly the surfaces and the convergence of the k point grid was checked for each case. Table 2 summarizes the main characteristics of these reconstructed surfaces. 

Figure 16.3 Surface model of the relaxed (001) cleavage plane of an alkali halide M+X with the rock salt structure. Shown are the topmost three layers containing both, cations (black balls) and anions (open balls). The local symmetry of the surface is...

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