R. C. Newman

Bio: R. C. Newman is an academic researcher. The author has contributed to research in topics: Dislocation. The author has an hindex of 1, co-authored 1 publications receiving 69 citations.

The spacing of prismatic dislocation loops

Abstract: The stresses round a circular prismatic dislocation loop are determined and used to calculate the spacings between such loops in a row generated from a source of internal stress. The results are consistent with the available experimental observations.

Work hardening of dispersion-hardened crystals

Abstract: A new theory of work hardening in dispersion-hardened single crystals—by which we mean soft crystals containing hard non-deforming particles of a second phase—is described. It is based on the fact that, if the particles do not deform plastically, and the interface between particle and matrix does not fracture, then secondary slip must occur locally round each particle when the crystal is deformed, even though the crystal may appear to deform by ‘single slip’. The density of secondary dislocations rises steeply with strain, and acts as a forest impeding the movement of primary glide dislocations. The theory predicts a relation between stress and strain (eqn. (9)) which is in good agreement with experimental results. Fracture of the particle-matrix interface, and the importance of the strength of this interface, are discussed.

The theory of diffuse X-ray scattering and its application to the study of point defects and their clusters

Abstract: The theory of the diffuse scattering by point defects and by defect clusters is reviewed. For a small concentration of statistically distributed point defects the symmetry of the long ranging part of the displacement field and the strength of the defects can be obtained from scattering measurements close to the reciprocal lattice points (Huang scattering). In addition to the (symmetrical) Huang scattering an asymmetry of the scattering is observed. For defects with sufficiently large displacements, the sign of this asymmetric scattering determines the sign of the displacement field around the defect and its magnitude yields information about the magnitude of the displacements close to the defect. For defect clusters the diffuse scattering is strongly modified. The Huang scattering very near to the Bragg reflection increases in direct proportion to the number of point defects in the cluster. For larger distances q from the Bragg reflection the intensity decreases as 1/q4.

Defects in silicon

Abstract: The method of obtaining pure polycrystalline silicon is described, followed by short accounts of how this material is converted into single-crystal form either by the Czochralski (CZ) pulling method or the float-zone (FZ) method. It is shown that the silicon contains various impurities including oxygen, carbon, boron and possibly hydrogen. The defects and impurities often show a nonhomogeneous distribution in the form of helical swirls. Heat treatment of silicon-containing oxygen leads to the clustering of this impurity. At 450 degrees C there is formation of small complexes that act as shallow donors. Investigations using IR and ESR spectroscopy have so far failed to determine the atomic configuration of the defects. Heating at higher temperatures causes wide-scale precipitation of oxygen. There are interactions with carbon and there can be formation of silicon carbide precipitates. Contamination from Cu, Au, Fe, etc., can occur during these treatments and methods for gettering these metals are discussed, involving dislocations and silica precipitates. Low-temperature irradiations produce vacancies and self-interstitials which combine with impurities to form complexes on heating from 4K to 300K. Evidence is presented to illustrate the possible charge states of self-interstitials. Damage produced by fast neutrons is discussed next, followed by a brief account of neutron transmutation doping whereby neutrally occurring 30Si is converted to 31P by the capture of thermal neutrons. Some aspects of high-temperature diffusion are discussed and attempts are made to correlate the data with that derived from the irradiation studies.

Dislocations and stacking faults

Abstract: The properties of linear defects in crystals (dislocation lines) and of planar defects (stacking faults) are important in almost every branch of solid state physics. This article is intended to give a comprehensive introduction to dislocation theory for the physicist who is not a specialist in crystal plasticity. It begins with a survey of the established theory relating to the geometrical and topological properties of dislocations, the elastic theory of dislocations in a continuum, the atomistic or core properties of dislocations, and the dynamics of moving dislocations. General methods for finding the elastic field of an arbitrary dislocation loop are outlined, and the results of some recent calculations using anisotropic elasticity are summarized. These include the prediction, partially confirmed by experiment, that dislocations in certain ranges of orientation may have negative line tension. The current importance of atomistic calculations of core structure and related problems is emphasized, and the methods available for these calculations are discussed. More detailed descriptions of dislocation and stacking fault configurations are given for some of the common crystal structures, and recent work on complex defects resulting from vacancy aggregation in close-packed structures is included. The experimental and theoretical evidence for the recent conclusion that screw dislocations in body-centred cubic metals have an asymmetric core is also reviewed. The rather controversial theory of thermally activated dislocation motion is described in a separate section, and examples are given of the application of this theory to various models of the obstacles encountered by moving dislocations. The final section is concerned with the theory of dislocations in grain boundaries and interphase boundaries, and includes the concept of the surface dislocation tensor.

Neutron-irradiated molybdenum: relationship of microstructure to irradiation temperature.

Abstract: The microstructural defects produced in molybdenum by neutron irradiation in the temperature range 50 °C to 800 °C have been characterized by transmission electron microscopy. At a low irradiation temperature, 50 °C, a large number of small dislocation loops, presumably interstitial, form within a complex dislocation network. At intermediate temperatures, 400–600 °C, small interstitial loops agglomerate into rafts. At high temperatures, 600–800 °C, the small loops which comprise a raft are sufficiently mobile to form large loops which interact with each other to produce a coarse dislocation network. The migration of small loops through the lattice by a combination of prismatic glide and conservative climb accounts for the observed microstructures. Vacancy loops are the only identifiable vacancy defects at temperatures ≥ 500. Between 575–650 °C, both vacancy loops and voids exist. Above 650 °C to at least 800 °C, voids are the exclusive vacancy defect. Information on the effect of impurities and g...