Dislocation arrangements in cyclically deformed polycrystalline molybdenum

The present paper deals with the cyclic stress-strain behaviour of polycrystalline molybdenum at room temperature and the dislocation structures built up within this material during the fatigue process. A cyclic stress-strain curve of molybdenum deformed in a strain-controlled and symmetrical push-pull test is shown. At strain amplitudes e_a < 3 × 10⁻³ arrangements of relatively homogeneously distributed dislocations are observed in the stage of the stabilization of mechanical properties. The characteristics of these dislocation arrangements are similar to those of dislocation structures of unidirectionally deformed molybdenum single crystals. At strain amplitudes e_a > 3 × 10⁻³ dislocation structures are developed with an inhomogeneous dislocation distribution (bundles structures). The dislocation density in the surface layers of fatigued specimens shows larger values than within the material. The cyclic deformation after a change from a small deformation amplitude to a larger one, or vice versa, is connected with characteristic changes of dislocation density.     

Dislocation Photoconduction and Related Dislocation Memory Effects in KCl Crystals

Two types of memory phenomena are discussed, both related to dislocation photoconduction of highly pure and coloured KCl crystals, using the combination of Lyman- and F-illuminations. A very simplified explanation of the dislocation memory effects is given taking into consideration possible changes in the direction of the photocurrents. Some considerations may be of interest for the explanation of photoplastic effects.     

Positron trapping in deformed Gd

Positron lifetime and Doppler broadening measurements have been used to study the annealing behaviour of deformed Gd between 290 and 700 K. The observed recovery stage at about 370 K is attributed to dislocations annealing.     

Light-induced creation of defects related to low energy photoluminescence in hydrogenated amorphous silicon

We have studied intensity and lifetime distribution of low energy photoluminescence (PL) in a-Si:H films containing native defects of various densities, prepared at various substrate temperatures, and those containing photo-created defects after illumination of pulsed light from a YAG–OPO laser system. A relation between the density of dangling bonds (DBs) and intensity of low energy PL is obtained for the films before illumination. The low energy PL in the films after illumination is stronger than that expected from the relation. The illumination does not cause sizable change of the lifetime distribution of the low energy PL of 0.95 eV. These results suggest a strongly inhomogeneous spatial distribution of photo-created DBs.     

Dislocation etching in V3Si

Dislocations in as-grown and in plastically deformed V₃Si single crystals have been studied by chemical etching. In as-grown crystals dislocations are partly arranged in small-angle boundaries parallel to {001}, {011}, and {112} planes. The total dislocation density amounted to (10⁵−10⁶) cm⁻². After plastic deformation at elevated temperatures indications for slip and climb processes were observed. The dislocation density increased to 10⁷ cm⁻².     

Distribution of dislocation density in deformed polycrystals

Dislocation density fluctuations over randomly oriented crystals are reliably distinguishable against the Poisson noise background. A systematic reduction of fluctuations is observed with increasing order in crystal orientations.     

Temporal electric conductivity variations of hydrogenated amorphous silicon due to high energy protons

Electric conductivity variations of undoped, n-type and p-type hydrogenated amorphous silicon (a-Si:H) thin films irradiated with various energy protons are systematically investigated. Dark conductivity (DC) and photoconductivity (PC) of the undoped samples increase at first due to proton irradiation and then decrease dramatically with increasing proton fluence. The increase in DC and PC becomes greater with increased proton energy. However, this increase is metastable and gradually decreases with time at room temperature. Similar results are observed in the n-type a-Si:H, whereas only a monotonic decrease is observed in DC and PC for the p-type samples. The increase of both DC and PC due to proton irradiation is attributed to metastable donor center generation. On further irradiation both the DC and PC decrease by the accumulation of radiation-induced defects, which act as deep traps and compensate carriers. The decrease in DC and PC becomes less pronounced as the proton energy increase and can be fitted along a universal line when the proton fluence is converted into displacement per atom (dpa).     

Dislocation luminescence of germanium

The dependence of dislocation luminescence of p- and n-Ge is investigated using different doping concentrations and ranges of pumping power. Three luminescence bands can be chosen. The main band (0.5 eV) is supposed to be due to the transition of the conduction band electron to the dangling bond, and is effective at any experimental conditions. Two other bands are rather sensitive to the dopant type. This enables us to suggest the model of the corresponding transitions in donor-acceptor recombination terms.     

Photoluminescence from deformed CaO crystals

The plastic deformation of CaO crystals produces the increase of luminescence band centered at 385 nm and 454 nm. The bands are excited with light of 350 nm and 275 nm respectively, and their relative increase depends on the kind of deformation applied to the crystal. The results are compared with previous cathodoluminescence observations.     

Dislocation etch pits in anhydrous diglycine sulfate

New dislocation etchants for anhydrous diglycine sulfate single crystals have been developed and the etching results are reported. Dichloroacetic acid, glacitel acetic acid and their mixtures work as dislocation etchants on the cleavage plane of the crystal. Morphology of the etch pits was found to vary with the etchant composition.     

Dislocation mobility in LiF at low temperatures

The mobility of dislocations in LiF has been measured at 4.2 and 10 K by means of an etch pit technique. The average velocity of screw dislocations is 2–5 times as large as edge dislocations. The results of the stress and temperature dependence of the velocities correlate well with the data of the critical shear stress in the same temperature region, and are well described by the theory of Peierls mechanism with thd Peierls stress of about 20 MPa for edge dislocations on {110} slip plane.     

Dislocation density in heteroepitaxial indium arsenide layers

In As layers have been grown by CVD on (111)B-oriented GaAs substrates. The dislocation density (N_D) distribution through the layer thickness has been studied. N_D is dependent on the mole fraction of AsCl₃ in the gaseous phase and, consequently, on the current carriers concentration. This results in the supposition that the decreasing of N_D in the layers after a “critical” thickness is due to the “pinning” of dislocations at impurity atoms which form stronger bonds with the host In or As atoms than the bond In–As, an effect which is known for bulk GaAs and InP crystals.     

Electron spin resonance studies of microcrystalline and amorphous silicon irradiated with high energy electrons

Paramagnetic defects in μc-Si:H and a-Si:H with various structure compositions were investigated by electron spin resonance (ESR). The defect density was varied by high energy electron bombardment and subsequent annealing. The spin density increases by up to 3 orders of magnitude. In most cases the initial spin density can be restored upon annealing at 160 °C.     

Dislocation generation around cylindrical pores

The formation of dislocation arrays reflecting the crystallographie symmetry of the surface pores formed by a mechanism of pitting corrosion was observed. The hypotheses developed in connection with the origination of dislocations around cylindrical pores by the effect of capillary forces led to process parameters whose estimated values agree well with those experimentally obtained. It is pointed to the importance of this process for the shrinkage during sintering.