Dissociation Widths Research Articles

On the asymmetrical dissociation of Lomer dislocations

Abstract Using anisotropic elasticity theory, Korner, Schmid and Prinz have shown that Lomer-Cottrell dislocations in the f.c.c. structure have asymmetrical equilibrium positions. This is also true for the isotropic theory, but in addition it can also be demonstrated in a very simple way that the ratio of the dissociation widths on the two {111} planes is material independent. This result seems to be general even for the anisotropic case. However, careful observations of Lomer dislocations in copper by weak-beam transmission electron microscopy indicate clearly that they are not dissociated.

Resonant states and photodissociation cross sections in protonated rare gases

Highly accurate interaction potential functions obtained earlier by us for NeH+ and ArH+ have been used to compute the entire manifold of quasibound states within a given range of possible widths. Semiclassical and quantal methods were employed and compared for both diatomics, showing very good accord with each other. General dipole functions are then extracted from a combined use of ab initio and model calculations, and employed to evaluate transition moments and then used to compute theoretical photodissociation cross sections and asymmetry parameters β(E). Resonant dissociation widths and positions are finally compared with the same quantities from the direct predissociative process and results are discussed vis à vis possible experiments on the present systems.

Dislocation dissociation widths in silicon at low temperature under controlled high-stress orientations

Abstract Dissociation widths of dislocations in silicon submitted to high stress and low temperature (HS/LT) are reported. In the first part of the paper, force systems (glide and climb components) acting on a pre-existing dissociated dislocation loop are analysed in terms of the deformation compression axis K. Then two main force systems are experimentally examined: (i) static cases for which the whole dislocation is at rest while partials are submitted to forces with directions which should result in a narrowing or a widening of the stacking fault ribbon; and (ii) dynamic cases (K = 〈120〉) with very different force systems. In all cases stacking faults have been found to be intrinsic. Climb forces seem to act on friction forces of 30[ddot] partials according as to whether they are positive or negative. Models developed by Alexander to explain the mobility of dislocations in the HS/LT conditions cannot account for our results. It is suggested that point defects could have an important effect on the mobil...

Partial separations of extended α and β dislocations in II–VI semiconductors

Abstract The dissociation widths of extended dislocations in CdTe, CdS and ZnTe have been measured using the weak-beam technique of electron microscopy, for α and β dislocations separately. Values of the stacking-fault energies have been determined. The experimental results agree with the modified ionic charge model of dislocations in the II–VI semiconductors, and not with the pure ionic model.

Plastic deformation of GaAs single crystals at room temperature and the influence of doping

Abstract The plasticity at room temperature of intrinsic, n- and p-doped GaAs single crystals has been studied in uniaxial compression under a confining pressure of 1 4 GPa. The n-type crystals were found to be softer than intrinsic or p-type crystals, in contrast to previously reported experiments carried out at intermediate temperatures. This feature can be related to the deformation substructure which exhibits long screw dislocation segments and evidence of cross slip. Microtwinning was also observed as well as large dissociation widths.

The dislocation structure of a 10° [110] tilt boundary in silicon

There have Been a number of studies of low-angle, θ < 4°, [10] tilt boundaries in the diamond lattice. Dislocations with Burgers vectors a/2<110>, a/2<112>, a<111> and a<001> have been reported in melt-grown bicrystals of germanium, and dislocations with Burgers vectors a<001> and a/2<112> have been reported in hot-pressed bicrystals of silicon. Most of the dislocations were found to be dissociated, the dissociation widths being dependent on the tilt angle. Possible dissociation schemes and formation mechanisms for the a<001> and a<111> dislocations from the interaction of lattice dislocations have recently been given.The present study reports on the dislocation structure of a 10° [10] tilt boundary in chemically vapor deposited silicon. The dislocations in the boundary were spaced about 1-3nm apart, making them difficult to resolve by conventional diffraction contrast techniques. The dislocation structure was therefore studied by the lattice-fringe imaging technique.

Dislocation structures and motion in II–VI semiconductors

Glide dislocations in CdS and CdTe have been studied by transmission electron microscopy, using the weak-beam technique. Dislocation glide planes, Burgers vectors and types (α or β) were identified. In both materials, both α and β dislocations were found to be dissociated, with dissociation widths corresponding to γ = 9.7±1.7 mJ m-2 (CdTe) and γ = 85±21 mJ m-2 (CdS). The values of γ for α and β dislocations in CdTe were determined separately, and found not to be significantly different.Dislocation motion in CdS and CdTe was observed, in situ, in the electron microscope, and the dislocations were seen to remain dissociated during motion.

Dislocation Dissociation in MgQnAl2O3 Spinels

ABSTRACTThe structure of low-angle tilt boundaries in magnesium-aluminate spinel has been studied by transmission electron microscopy. Special low-angle boundaries have been prepared from bicrystals but also boundaries in polycrystalline spinels were studied. The dislocations were all dissociated into partials. Their dissociation widths were found to increase with deviation from stoichiometry. Observations at lattice dislocations indicate that the composition at the boundaries may be different from the nominal composition.