Geometry Of Dislocations Research Articles

Misfit dislocations in semiconductors

The geometry of misfit dislocations in (100), (110) and (111) interfaces in the diamond-and sphalerite-structures is outlined. The geometry applies both to heterojunctions and to diffusion fronts. The effects of the non-centrosymmetry of the sphalerite structure are treated. The experimental evidence of diffusion-induced dislocations is reviewed and the electrical effects of the dangling bonds associated with misfit dislocations in heterojunctions are discussed.

The geometry of charged dislocations in the NaCl structure

AbstractVarious dislocation configurations are examined in the NaCl structure for the presence of localized electrostatic charge assuming slip systems of the {110} 〈110〉 type. Pure edge and screw dislocations do not display an effective electrostatic charge. However, edge dislocations that possess a jog length of a √2/4 or an abrupt kink length of a √2/8 display a virtual charge of ± q/2 whereas edge dislocations that possess a jog length of a √2/2 or an abrupt kink length of a √2/4 are electrically neutral (a is the lattice parameter and q is the ionic charge). Similarly, screw dislocations that possess a jog length of a √2/4 or an abrupt kink length of a/4 display a virtual charge of ±q/2 whereas screw dislocations that possess a jog length of a√2/2 or an abrupt kink length of a/2 are electrically neutral. Either type of jog can be formed on a dislocation, but charged kinks must occur in electrically neutral pairs. Intersection between dislocations on orthogonal slip planes yields only neutral jogs whereas intersection between dislocations on oblique slip planes yields only charged jogs and neutral kinks. Nodes formed by the intersection of n edge dislocations display a virtual charge of ±q/2 whenever n is odd (n ≠ 1) and are electrically neutral otherwise. The emergence point of a dislocation on an atomically flat surface always is neutral although the point may acquire a charge of ±q by ion transport. In general, the presence of a charge of ±q/2 denotes an infinite source (or sink) for anion and cation vacancies whereas a charge of ±q denotes an expendable source.

Dislocation Geometry of Crystalline Mercury

AbstractThe predominant slip direction of crystalline mercury is not the closest‐packed direction. In order to explain this and related observations, a geometrical analysis has been made of the types of dislocation which may be present in the mercury structure. Two approaches have been adopted. The first of these is based on the well‐established dislocation geometry of face‐centred cubic crystals; it does not lead to an adequate understanding of the experimental results. A satisfactory explanation of the observations is obtained, however, in the second approach, which considers the stacking sequence of the mercury slip planes. Some general implications of the results are discussed.

The distribution of dislocations in annealed tantalum

The density and distribution of dislocations in three dilute alloys of tantalum containing oxygen, nitrogen and carbon have been determined by transmission electron microscopy after 90% cold work and subsequent annealing between 900° and 1,750°C. Annealing below 1,200°C results in a marked decrease in the dislocation density and the formation of regular arrays of dislocations in sub-boundary networks. Above 1,200°C the sub-boundaries are removed. The changes are sensitive to impurity content. The geometry of dislocations in regular networks have been studied using a stereographic method. Over 60% of the networks examined were probably formed by the intersection of two parallel sets of a 2 〈 III 〉 dislocations.

XXV. The direct observation of dislocation nets in rock salt single crystals

Abstract A method for decorating dislocation lines in rocksalt single crystals is described. The method consists in colouring the crystals additively by means of sodium metal. It is found that specks are formed along the dislocation lines, which are, as a consequence, visible in ultra microscopic observation. It is thought that the specks are colloidal sodium particles, and an explanation is given for the decorating mechanism. The method is used for the study of the geometry of dislocations in deformed and annealed single crystals (i.e., polygonized). Hexagonal, square and lozenge shaped networks, as well as sets of parallel lines are found. Deviations from the ideal pattern are discussed from a theoretical point of view and compared with observations. It is found that the density of decorating particles is a function of the orientation of the dislocation line with respect to its Burgers vector. Evidence is found that screw dislocations are not decorated; it is further concluded that the nodes of a network are decorated preferentially. The emergence points of the dislocation lines correspond to the centres of the etchpits produced by the methyl alcohol etch.