Velocities of individual dislocations have been measured in LiF, covering a range of twelve orders of magnitude in velocity, from 10−7 cm/sec to 105 cm/sec. The velocity is extremely sensitive to applied stress at low velocities, and for each crystal there exists a minimum stress for dislocation motion, below which dislocations do not move. The edge components of dislocation loops move considerably faster than the screw components. The upper limit for dislocation velocity appears to be the velocity of sound in the crystal. The effects of temperature, impurities, and radiation damage on dislocation velocity are described. These variables affect the dynamic resistance to motion encountered by a moving glide dislocation.The growth of total dislocation density, the growth of individual glide bands, and the distribution of glide dislocations during plastic deformation are described.The yield stress of LiF is determined by the resistance to motion encountered by a glide dislocation in moving through an otherwis...

Dislocation Velocities, Dislocation Densities, and Plastic Flow in Lithium Fluoride Crystals

When exposed for the first time to materials engineering, students often ask: “Why study dislocations? Why can’t we get an engineering diploma without making this effort?” Such questions did not cross the minds of Taylor, Orowan and Polanyi, the fathers of modern dislocation theory in 1934, when they independently suggested their novel theory of dislocations, following concepts developed by Volterra in 1905. Their basic insights were crucial for the development of the modern science of structure, for the understanding of structural properties and, in particular, for the essential concept of the deformation of materials. A dislocation, due to its extent, is considered to be a line defect and is one of the various types of defects found in materials which determine each and every property of a crystal. Briefly, materials are not perfect and contain a variety of defects. These defects, that determine the properties of a material, are:

Introduction to Dislocations

Anisotropic etching of silicon has become an important technology in silicon semiconductor processing during the past ten years. It will continue to gain stature and acceptance as standard processing technology in the next few years. Anisotropic etching of

Anisotropic etching of silicon

To explain the rapid diffusivity of copper in germanium and its dependence on structure, it is proposed that the copper be dissolved in two states, interstitial and substitutional. It is deduced that in the interstitial state the solubility of copper is about ${10}^{\ensuremath{-}2}$ times less and the diffusivity many orders of magnitude greater than in the substitutional state. Conversion from the interstitial to the substitutional state is effected by lattice vacancies which are generated at free surfaces and dislocations; this accounts for the structure dependence of the diffusivity observed by Tweet and Gallagher.

Mechanism of Diffusion of Copper in Germanium

Publisher Summary This chapter discusses the progress in the field of plasticity of the diamond cubic structure (D.S.) from the standpoint of a micromechanical (dislocation dynamical) theory of macroscopic plastic properties. It is suggested that hat the high resistance to dislocation motion of D.S. crystals stems from a high Peierls potential. The problem is to understand the creation and movement of kinks as the elementary vehicles of dislocation motion. How do kinks interact with each other and with other lattice defects, including phonons? How does a distribution of kinks arise which shows up in the shape of dislocation lines frozen-in after deformation and observed in electron transmission? Semiconductor doping provides a unique possibility for manipulating the core structure of the dislocation in the D.S. and thus the Peierls potential. Its effect shows up microscopically in the dislocation dynamics as well as macroscopically in the deformation curves of D.S. crystals. The study of the charge on a dislocation in a doped semiconductor by measurement of its electrical properties discussed that may serve as a link in understanding the doping effects in dislocation dynamics.

Dislocations and Plastic Flow in the Diamond Structure

Precipitates formed by copper diffused into silicon crystals were studied by optical means using an infrared image tube. Linear aggregates are identified as dislocations by correlation with etch pits. Dislocations in as‐grown crystals are usually curvilinear. Dislocation loops formed during plastic deformation consist of straight‐line composite portions and pure screw portions, all of which lie in 〈110〉 directions. Precipitates frequently are not found on screw dislocations; when present they differ in detail from those on composites. Interactions between adjacent dislocations can be seen. Etch pits associated with either composite or screw dislocations are similar in form, indicating that the pits formed in as‐grown crystals by the technique described identify all the dislocations. Dislocation loops enter from the surface upon deformation of crystals with relatively few grown‐in dislocations. Dislocation loops formed entirely within the crystal in patterns consistent with operation of the Frank‐Read mech...

Copper Precipitation on Dislocations in Silicon

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Copper Precipitation on Dislocations in Silicon