Dislocation, screw

Dislocations. Screw dislocations are the most important defects when crystal growth is considered, since they produce steps on the crystal surface. These steps are crystal growth sites. Another type of dislocation of interest for metal deposition is the edge dislocation. Screw and edge dislocations are shown in Figure 3.4. 

The interaction energy between a solute particle (impurity atom, point defect) and an edge dislocation (screw dislocations do not interact, to first order) is... 

This is slip that occurs simultaneously on several slip planes having Ihe same slip direction. See Fig. 14. This type of plastic deformation is normally associated with the movement of screw dislocations. Screw dislocations can move on any slip plane that passes through the dislocation. This is a result of the fact that the slip plane of a dislocation is that plane which contains both the dislocation and its Burgers veclor, and the fact that the Burgers vector of a screw dislocation lies parallel io the dislocation itself,... 

For the weathering of trace minerals from the solid matrix, the dissolution occurs selectively on spots where the mineral is exposed to the surface. These mineral surfaces are usually not smooth, but show dislocations (screw, jump, step dislocations) and point defects (vacant sites, interstitial sites) (Fig. 23 left). Dissolved ions are immediately transported from the surface into solution, so that no gradient can develop. Since the total concentrations of trace minerals in the solution are low, no equilibrium can be reached. In the following the dissolution of trace minerals is called surface-controlled. 

From atomistic aspects, a metal can be considered as a fixed lattice of positive ions permeated by a gas of free electrons [1], Positive ions are the atomic cores, while the electrons are the valence electrons. Since there are about 1022 atoms in 1 cm3 of a metal, one can expect that some atoms are not exactly in their right place. Thus, one can expect that a real lattice will contain defects (imperfections). The most common defects are point defects (e.g. a vacancy, an interstitial) and dislocations (e.g. the edge dislocation, screw dislocation) [2]. 

KRI 63] KRIVOGLAZ M.A., RYBOSHAPKA K.P., Theory of X-ray scattering by crystals containing dislocations, screw and edge dislocations randomly , Fiz. Metal. Metalloved., vol. 15, p. 18-31,1963. 

Figure 1.14 Screw dislocation. Screw dislocation results if the planes of a lattice are twisted. (Reproduced with permission from Ref. [34], 2000, Hanser Verlag.)...

Three major types of line defects edge dislocations, screw dislocations, and antiphase defects) are summarized here. The Hne defects are generally important factors in the electrical behavior of semiconductor devices since their influence (as trapping centers, scattering sites, etc.) extends over distances substantially larger than atomic spacings. 

Dislocation, screw, 754 Dispersion, 239. See also Peptization, Stability of sols Displacement, immiscible, 471 Disproportionation, 506 Dissipation, energy, 305-306, 677 Dissociative chemisorption, 645, 649, 650 of ammonia, 658... 

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