Dislocation Etch Pits Research Articles

Various Dislocation Etch Pits Revealed on LPE GsAs{001} Layer by Molten KOH

Various Dislocation Etch Pits Revealed on LPE GsAs{001} Layer by Molten KOH

Dislocation substructure of mantle-derived olivine as revealed by selective chemical etching and transmission electron microscopy

Cleaved and mechanically polished surfaces of olivine from peridotite xenoliths from San Carlos, Arizona, were chemically etched using the techniques of Wegner and Christie (1974). Dislocation etch pits are produced on all surface orientations and they tend to be preferentially aligned along the traces of subgrain boundaries, which are approximately parallel to (100), (010), and (001). Shallow channels were also produced on (010) surfaces and represent dislocations near the surface that are etched out along their lengths. The dislocation etch channel loops are often concentric, and emanate from (100) subgrain boundaries, which suggests that dislocation sources are in the boundaries. Data on subgrain misorientation and dislocation line orientation and arguments based on subgrain boundary energy minimization are used to characterize the dislocation structures of the subgrain boundaries. (010) subgrain boundaries are of the twist type, composed of networks of [100] and [001] screw dislocations. Both (100) and (001) subgrain boundaries are tilt walls composed of arrays of edge dislocation with Burgers vectors b=[100] and [001], respectively. The inferred slip systems are {001} 〈100〉, {100} 〈001〉, and {010} 〈100〉 in order of diminishing importance. Exploratory transmission electron microscopy is in accord with these identifications. The flow stresses associated with the development of the subgrain structure are estimated from the densities of free dislocations and from the subgrain dimensions. Inferred stresses range from 35 to 75 bars using the free dislocation densities and 20 to 100 bars using the subgrain sizes.

Influence of adsorbed fluids on the rolling contact deformation of MgO single crystals

Basic phenomena associated with rolling contact deformation were studied using MgO as a model bearing material. A hardened steel ball was rolled on MgO single crystals in slow speed reciprocating motion and in high speed circular motion. The resulting deformation was studied by dislocation etch pit techniques. The presence of adsorbed fluids, such as silicone oil, white mineral oil and toluene, with slow speed sliding caused a dramatic change in slip mode and premature surface spalling compared with similar experiments in air or under water. In contrast dimethyl formamide inhibited these slip processes. The results are consistent with the dependence of dislocation mobility on adsorbed species. High speed hydrodynamic rolling with mineral oil lubrication produced a different slip phenomenon entirely than that produced by slow speed rolling. The slip bands resembled those produced in tensile tests and all slip apparently initiated at subsurface sites.

Some Observations of Dislocation Etch Pits on {111} Surfaces of Cu and Cu–Al Dilute Alloy Crystals

Some Observations of Dislocation Etch Pits on {111} Surfaces of Cu and Cu–Al Dilute Alloy Crystals

Reveal of dislocation etch pits on {001} GaP with hot phosphoric acid

Reveal of dislocation etch pits on {001} GaP with hot phosphoric acid

Matrix behavior in copper-tungsten composites at small strains

Composites with up to 15 pct tungsten wires in a copper crystal matrix prepared by infiltration showed matrix microyield and flow stresses increasing with fiber fraction. Dislocation etch-pit observations showed that the walls of a cell structure in the matrix formed during fabrication were the operative dislocation obstacles and that this initial structure rather than fiber-matrix interaction during straining was responsible for the matrix strengthening.

Dislocation etch pits in galena

The results of dislocation etch pit studies of naturally and experimentally deformed galena single and polycrystals are presented. The etch pitting is simple, inexpensive, rapid and reveals dislocation substructures similar to those found in metals and ceramics. Both {110} < 11̄0 > and {100} < 110 > type slip systems have been found in naturally and experimentally deformed galena.

Etching behaviour of calcium fluoride crystals in hydrochloric acid vapour

AbstractEtching of octahedral cleavage faces of calcium fluoride crystals in hydrochloric acid vapour has been investigated. It is observed that dislocation etch pits and non‐dislocation elevations are formed. The morphology of etch pits obtained by vapour etching is observed to be different from that obtained by weak acid solutions. The results are discussed in terms of the prevailing etching conditions.

High Electron Mobility Silicon Films Grown on Sapphire at High Growth Rate

Electron mobility of N-type (100) plane silicon films 1 µm thick on (11̄02) sapphire substrate has been investigated associating with the growth rate. High electron mobility, near 600 cm2V-1s-1, has been achieved at 10∼20 µ/min high growth rate. Dislocation etch pits and stacking fault patterns have been revealed by the newly developed chemical etching. The dislocation density decreases at low growth rate region (<2 µ/min) with increasing growth rate. At high growth rate, more than 10 µ/min, stacking fault density decreases. The in-depth profiles of auto-doped aluminum have been obtained by the ion mass spectrometry. As a result, mobility enhancement at the high growth rate is assigned to stacking fault decrements in the films.

Causes of the formation of etch pits of different size and morphology on {100} faces of CsI crystals

AbstractCauses of the formation of dislocation etch pits of different shape and size on {100} faces of cesium iodide crystals by an etchant composed from 25–35 mg/1 CuCl2 · 2 H2O in 96% ethanol are studied. It is shown that one of the reasons of the change in the morphology of etch pits is the segregation of excessive iodine at dislocations.

CuおよびCu-Al希薄合金結晶の{111}面転位ピットの形態について

CuおよびCu-Al希薄合金結晶の{111}面転位ピットの形態について

Dislocation etch pits on various crystal planes of silicon

Dislocation etch pits on various crystallographic planes of silicon are reported and the nature of their shapes in the plane of observation has been discussed in confirmation with the crystal structure. The crystallographic planes studied are divided into two categories: (i) low energy planes, (ii) high energy planes. It has been observed that the solution containing HF, CrO 3 and H 2O is versatile and by proper adjustant of CrO 3 the dislocation etch pits on both low energy and high energy planes can be delineated. Our observations lead to the conclusion that the minimum angle for getting the trace of {111} planes delineated on the plane of etching is around 35° and this seems to be the controlling factor for the geometry of the etch pits.

Dislocation etch pits in gold

Newly developed etch-pitting technique for gold is reported. A one-to-one correspondence is obtained between etch pits and dislocations, with etchants of 1∶3 aqua regia and aqua regia plus suitable modifiers. The usefulness of these etchants has been established by several experimental results, such as the appearance of etch pit rosette patterns produced by indentation, correspondence between slip line and pit arrays in deformed crystals and climb polygonization arrays after annealing. It is also confirmed that the etchants are capable of differentiating positive and negative edge dislocations.

Etch pits and dislocations of Ga1−xAlxAs liquid phase epitaxial layers

The etch pits of Ga1−xAlxAs are revealed by the etchant (H2O/H2O2/CH3COOH/HF) and it is verified that these etch pits correspond faithfully to dislocations using x-ray transmission topographs. The shapes of dislocation etch pits which are revealed by the etchant (1 H2O/1 H2O2/2 CH3COOH/0.5 HF) are either conical on the (100) face of Ga1−xAlxAs with x≳0.1 or pyramidal on the (100) face of Ga1−xAlxAs with x=0.05.

A dislocation etchant for {100} gallium phosphide

An etchant has been developed which produces etch pits with a well-defined crystallographic structure on {100} gallium phosphide surfaces. Scanning electron microscope (SEM) studies using both the emissive and cathodoluminescent (CL) modes of operation have established that there is a precise 1:1 correlation between etch pits and dark dots seen in the CL micrographs. Since the dark dots in the CL image are produced at the sites of emergent dislocations, it is therefore concluded that the etch pits are dislocation etch pits. The described etchant makes possible a rapid and easy assessment of the degree of crystalline perfection of {100} gallium phosphide epitaxial layers.

Observation of dark line defects in GaP green LED’s under an external uniaxial stress

Dark line defects (DLD’s) have been observed in GaP green LED’s under an external mechanical stress. Excitation of minority carriers is essential to DLD formation. DLD is revealed to grow along the 〈110〉 direction and to correspond to an array of dislocation etch pits. A ’’traveling dark spot’’ was observed for the first time. It moves as fast as 1 mm/sec and becomes trapped at the edge of DLD, which results in DLD growing. DLD generation depends on both the forward current magnitude and external stress.

亜鉛単結晶の底面辷りの初期段階

An experimental study has been carried out to investigate the contribution of basal and nonbasal dislocations (forest dislocations) to the early stage of basal glide in 99.999% pure zinc single crystals compressed at room temperature. The relation between the basal shear stress and the shear strain was plotted and the increase of dislocation density during deformation was observed by means of the etch pit technique. The initial dislocation etch pit densities of the specimens used were 2.9×104∼3.7×104/cm2 on (0001) surface and 6.1×104∼5.2×105/cm2 on (11\bar20) surface. From these data, the length of basal and nonbasal dislocations per unit volume was calculated using equations developed by G. Schoeck. It was assumed that the density of forest dislocations did not change during the deformation since the critical resolved shear stresses for nonbasal slip systems are considerably higher than the stress employed in the experiments. The results obtained were as follows.(1) The multiplication stresses were approximately equal to the stresses required to break up the attractive junctions between basal and forest dislocations. (2) The yield stresses were represented by the sum of the stress necessary for the forest cutting and the internal stress due to the basal dislocations. From this result, it was concluded that the yield stress, was controlled by the forest cutting under the internal stress field of the basal dislocations.

Polarity in bending deformation of InSb crystals

Deformation characteristics of InSb crystals subjected to α-bending or β-bending are observed as a function of the strain rate and the temperature. Difference in the characteristics between the two types of bending is demonstrated. Higher flow stresses are observed in β-bending as compared with α-bending. No difference is found between the two types of bending in the magnitudes of parameters which characterize the strain rate and the temperature sensitivities of the yield stresses. Observations on slip bands as well as those of dislocation etch-pits show that dislocations on the secondary slip system are activated in β-bending. It is suggested that this is the cause of the observed higher flow stresses. It is shown that the motion of screw dislocations of the primary slip system controls the deformation rate in both types of bending.

Luminescence in deformed MgO, CaO and SrO

Abstract Plastic deformation in the alkaline-earth oxides results in optical absorption bands, the most pronounced of which occur at 5–7 eV in MgO, 4–6 and ∼5–8 eV in CaO, and 4–1 and ∼5–0 eV in SrO. Excitation in these energy regions generates luminescence bands, with peaks at 2–9 (violet), 2–6 (blue), and 2–3 (green) eV in MgO, CaO and SrO, respectively. The temperature- and anisotropy-dependence of the emission spectra gives clear indications that multi-bands are involved. The visible emission provides a convenient means of observing slip systems without artificial decoration techniques. Correlation between emission intensity pattern and dislocation etch-pit density has been demonstrated in MgO. The luminescence effect permits an instantaneous and clear observation of gross imperfections as they are being formed in a solid, either on the surface or in the bulk. Dynamic studies of dislocation interaction can be made. By monitoring the emission intensity as a function of stress and strain, it was found that the defects responsible for the emission are formed at the onset of plastic deformation.

Effect of dislocations on green electroluminescence efficiency in GaP grown by liquid phase epitaxy

The origins of dislocations in GaP grown by liquid phase epitaxy (LPE) and their effects upon green electroluminescence (EL) efficiency have been investigated by chemical etch pitting and scanning electron microscopy. Under normal growth conditions, the dislocation etch pit density (ρD) and configuration in the epitaxial layers are controlled by, and are approximately the same as, that in the liquid encapsulated Czochralski substrate. All dislocations which are revealed by chemical etching in the p LPE layer cause a localized reduction in luminescence. The dislocations are shown to behave as regions of rapid (nonradiative) recombination. Typically, reductions of a factor of ∼2 in green EL efficiency occur when ρD for the LPE layers is in the ∼2–5×105 cm−2 range, corresponding to an average separation of about two to four diffusion lengths in this material. The experimental results are supported by a simple theoretical model for the effects of dislocations on EL efficiency. These considerations explain why dislocations in GaP LPE layers for red light-emitting diodes (LED’s), in contrast to green LED’s, typically have no significant effect on EL efficiency since diffusion lengths are much shorter (≲2 μm) in the red LED’s.