Etch Pit Studies Research Articles

The brittle-ductile transition in silicon. II. Interpretation

A dynamic crack tip shielding model has been developed to describe the brittle-ductile transition (BDT) of precracked crystals in constant strain-rate tests. Dislocations are emitted from a discrete number of sources at or near the crack tip. At the BDT the dislocations are emitted and move sufficiently rapidly to shield the most vulnerable parts of the crack, furthest away from the sources, such that the local stress intensity factor remains below K Ic for values of the applied stress intensity factor K above K Ic . Computer simulations of the dynamics of dislocation generation from the crack tip sources, assuming mode III loading, suggest that a sharp transition as observed in silicon is predicted only if generation starts at K ≡ K 0 ≈ K Ic , but then continues at K ≡ K N ≪ K Ic . Dislocation etch pit studies reported by Samuels & Roberts ( Proc. R. Soc. Lond. A 421, 1─23 (1989)) (hereafter called I) confirm that generation begins at K 0 ≈ K Ic . It is suggested that K 0 corresponds to the value of K at which a crack tip source is nucleated by movement of an existing dislocation in the crystal to the crack tip. The model accounts quantitatively for the strain-rate dependence of the transition temperature T c reported in I, and predicts a dependence of T c on dislocation density, in qualitative agreement with (unpublished) experiments. Calcluations of the strees field around the crack tip of a semicircular precrack, suggest that the ends of the half loops emitted by crack tip sources undergo multiple cross slip to follow the crack profile. The predicted dislocation configurations agree with etch pit observations reported in I.

Experimental evidence for creation of luminescence quenching localized defects by moving dislocations in gallium arsenide

The production of luminescence quenching localized defects by moving dislocations in GaAs plastically deformed at 350 °C has been established by low-temperature (80 K) band-edge cathodoluminescence (CL) and chemical etch-pit studies. Specimens were deformed to two levels, (1) measurable macroscopic plastic deformation, and (2) 20% of the stress applied in (1). It was established by CL and chemical etching that numerous dislocations were generated on the four {111} stressed slip planes of the macroscopically deformed specimen. Uniform bands of reduced CL signal were correlated to bands of enhanced etching in the lightly deformed samples. It was established from the etching and CL images that these bands are not produced by deformation-induced dislocations but must consist of numerous localized luminescence quenching (Refs. 1–3) defects (e.g., point defects and small dislocation loops) created by the passage of dislocations.

Dislocations in HgCdTe-CdTe and HgCdTe-CdZnTe heterojunctions

Mechanisms that govern the generation and movement of dislocations in (111) heterojunctions of HgCdTe-CdTe and HgCdTe-CdZnTe grown by liquid phase epitaxy have been investigated with etch pit studies. The density and distribution of the misfit dislocations in these heterojunctions have been measured quantitatively and analyzed to clarify the mechanisms that generated them. The origins of the dislocations threading through the epilayer are also reported.

Etching studies on crystals of thallium arsenic selenide

Abstract An etchpit technique was developed and used to reveal the dislocations in crystals of thallium arsenic selenide (Tl3AsSe3). The etchpit density was higher near the surface of the cylindrical crystals than at the corresponding central region. Also the density was very high near the seed-bulk joint. Taken together these features suggest that the etchpits were related to stresses induced by the temperature distribution in the growing crystal. A calculation of the thermal stress distribution in the Bridgman-grown crystal by means of a finite element method supports the observations of the etchpit studies.

Growth and Characterization of Ti3PSe4 Single Crystals

ABSTRACTGood quality single crystals of Ti3PSe4 were grown from the melt by the Bridgman technique following improvements in the method of purifying the parent components, and optimization of growth parameters. Crack-free crystals 8 cm in length and 17 mm in diameter were produced.The quality of the crystals was evaluated by optical transmittance and metallographic techniques. In the range 0.7 to 14 μm the optical transmittance shows elimination of absorption bands exhibited in crystals grown without special purification steps. Etchpit studies showed that the crystals were free from inclusions and lamellar twins and that they show a uniform cross sectional etch pit density.

LATTICE MATCHING IN HgCdTe-CdZnTe HETEROJUNCTIONS

AbstractAn etch pit study has been made on misfit dislocations in (111) HgCdTe-CdZnTe heterojunctions grown by liquid phase epitaxy. It was shown that misfit dislocations were localized at the original surface of the substrate, because Zn diffused into the epilayer during epitaxial growth prevents movement of dislocations. For lattice matching between Hg0 7Cd0.3Te and Cd1−yZnyTe, the optimum ZnTe mole fraction of Cd1−yZnyTe was found to be 2.9%.

Dislocation motion in MgO crystals under plate impact

Dislocation dynamics in MgO single crystals is studied by means of plate impact experiments in which specimens are subjected to stress pulses of 214 to 376 MPa resolved shear stress with duration in the range of 0.09 to 0.23μsec. Dislocation structures in the recovered crystals are observed by an etch pit technique and by transmission electron microscopy. Etch pit studies show that inclusions play a role in the generation of interior glide bands and that there is a 20 to 40-fold increase in dislocation densities outside the glide bands. Assuming the average dislocation velocity is approximately proportional to the applied stress the drag coefficient for MgO at dislocation velocities of 1 to 2 km sec−1 is observed to be 5×10−5 Nsec m−2. Transmission electron microscopy determines the spacing and curvature of dislocations in glide bands.

Etch pit studies in alkali halide crystals

Among several techniques which have been developed for observing dislocations in crystals, etching technique is the most convenient and simplest method. The main aim of this report is to describe the results of a survey of etch pit studies undertaken in alkali halide crystals and to extend the available data in this field. This review lays emphasis on the application of etch pit method to study dislocations in alkali halide crystals. Different aspects of the problem presented include: 1.(i) A brief survey of various etchants reported for different alkali halide crystals.2.(ii) Role of etching parameters such as poison concentration, temperature, stirring, undersaturation of the solvent etc on etch pit morphology.3.(iii) Mechanism of etch pit formation.4.(iv) Mechanism involved in the orientation and morphological changes in etch pits.5.(v) Role of impurities on etch pit formation.6.(vi) Dissolution kinetics at dislocation sites.7.(vii) Surface dissolution.8.(viii) Dislocation velocity measurements.9.(ix) The origin and mechanism of formation of 'Anomalous solution phenomena' obtained on cleavage planes of alkali halide crystals.10.(x) The origin and mechanism of thermal etch pits in alkali halide crystals.

Dissolution kinetics and etch pit studies of potassium aluminium sulphate

The dissolution process of the {111} faces of potash alum is studied, both by microtopographic examinations of the etch pit patterns and by measurement of the dissolution kinetics in a rotating disc crystallizer. Both methods showed that the Cabrera-Levine dissolution theory holds for the two most common dislocation types ending on the {111} faces of potash alum. On the basis of the rotating disc experiments, the interfacial supersaturation of the etch pit experiments was roughly estimated. Using this, it was found that at interfacial supersaturations below -0.6% (dislocations with 〈110〉 Burgers vector) or below -0.85% (dislocations with 〈100〉 Burgers vector) numerous etch pits related to those dislocation types appeared. Below those undersaturations the dissolution process is mainly determined by volume diffusion. From the critical undersaturation, determined in the rotating disc crystallizer, the value of the edge free energy of a step was found to be approximately 0.01 J/m 2.

Liquid phase epitaxial growth and characterization of InAsxSb1−;x AND In1−yGaySb ON (111)B InSb substrates

Liquid phase epitaxial growth of InAsxSb1−x, for 0<x<0.27 and In1−yGaySb, for 0<y<0.37, has been successfully accomplished on (111)B InSb substrates between the temperatures of 450 and 520°C. The phase diagrams and the growth conditions for high-quality planar epitaxial layers have been determined. For growth of InAsxSb1−x for high values of x, the strong tendency of the ternary melt to dissolve the substrate, even when the liquid is a few degrees below its melting point, was negated by using large supercooling. Small supercooling of zero to 5.6°C were required over the whole range of composition examined for (In.Ga)Sb, whereas, for example, supercooling greater than 30°C was required to grow InAso.26Sbo.74 to avoid substrate dissolution. Lattice mismatch to the substrate was relieved by compositional grading. Etch pit studies in both materials yielded dislocation densities ranging from 5.8 × 102 to 2×106 cm−2 with most materials in the low 104 range. Hall and resistivity measurements performed at 300K and 77K on most samples showed an impurity contamination of the epitaxial layers. Some samples were n-type (carrier concentration approximately 1017/cm3), with varying degrees of acceptor compensation and others were n-type (carrier concentration approximately l017/cm3) at room temperature due to intrinsic conduction, but exhibited p-type conduction (carrier concentration approximately 5×l0l6/cm3) at 77K. Hall measurements performed on one of the latter samples ofvery low As content from 77K to 4.2K to examine hole freeze-out yielded an acceptor level ionization energy of 0.0126eV which is close to the effective mass acceptor level ionization energy in InSb. The electron-to-hole mobility ratio was also found to be 65.9. Electron microprobe analysis showed silicon to be the dominant impurity.

Anomalous I-V and burst noise characteristics associated with surface channels in an NPN integrated transistor

Electrical and etch-pit studies have been carried out on integrated NPN transistor arrays. In one array the devices had extensive ‘kinks’ in their I C-V BE curves. One device in this array also exhibited peculiar burst-noise behaviour. The anomalous I-V and burst noise behaviour has been attributed to the presence of surface channels between all three contacts plus a dislocation network in the base region.

Misfit dislocations in PbTe-PbSnTe heterojunction

Misfit dislocations at the heterojunction of PbTe-PbSnTe layers grown by liquid phase epitaxy have been investigated by etch pit studies. The linear density of misfit dislocations along the 〈100〉 direction parallel to the heterojunction was in good agreement with the predicted value. This agreement indicates that the strain due to lattice mismatch between PbTe and PbSnTe is completely relieved by the introduction of misfit dislocations. It has been shown from the distribution of etch pits, electron probe analysis, and calculations, that the misfit dislocations spread around the heterojunction in the region determined by Sn self-diffusion during epitaxial growth.

Anisotropy of surface oxide softening of niobium single crystals

Abstract Oriented single crystals of high purity niobium have been prepared with square cross sections such that edge dislocation lines were parallel to one pair of faces (E faces) and screw dislocation lines were parallel to the other pair (S faces). Anodic oxidation of the crystals caused a reduction of the critical resolved shear stress and the occurrence of serrated flow in the manner reported previously (Sethi and Gibala 1975). Selective oxidation of only the E faces resulted in the same reduced flow stress as when all faces were coated, whereas oxidation of only the S faces produced little change in flow stress. These results, together with other mechanical tests and complementary slip trace and etch-pit studies, illustrate that under applied stress the oxide coatings introduce large densities of mobile edge dislocations which are responsible for the enhanced plasticity.

Etch Pit Study of GaAs{001} LPE Layer by Molten KOH

Etch Pit Study of GaAs{001} LPE Layer by Molten KOH

In situ study of collective dislocation movements in a Ni-Cr alloy

Properties of groups of moving dislocations have to be considered in various deformation processes especially those of concentrated alloys (1). Indeed, the strain rate dependence on stress and temperature of such materials cannot be interpreted in terms of simple models postulating homogeneous deformation. Nevertheless experimental studies of these dynamic properties are rare and consist mostly of etch pit studies of the sequences of dislocation pile ups at various stages of the stress strain curve (2) or the dynamic recording of macroscopic slip trace development by high speed cinematography (3).We report here some microscopic properties of moving groups of dislocations in a FCC Ni-30 wt%Cr alloy observed directly during deformation tests in the high voltage electron microscope. This alloy has a rather low stacking fault energy (γ/Gb≃3.5xlO-3) and exhibits short range order after 100 hours of annealing treatment at 600°C. Between 77 K and 400 K, conventional deformation tests lead to rather small activation volumes indepedent of strain and a high athermal stress, incompatible with the intersection mechanism (4).

Etch pit study of dislocation breakaway in pre-yield deformation of copper single crystals

Three-point bending tests on Cu single crystals of low dislocation density and double etching are performed to study the stress dependence of breakaway of grown-in dislocations in the pre-yield region. By an appropriate annealing procedure after each experiment the specimen can recover its original condition which permits to compare experiments with changed parameters (temperature 77 and 300 K, loading time 6.7 ms to 1 s, impurity content, dislocation density). The results indicate that the characteristic sigmoidal dependence of breakaway on stress is mainly determined by the distribution of dislocation segment lengths between nodes in high purity specimens and between additional impurity clusters or jogs impeded by impurities in less pure specimens. Dreipunkt-Biegeversuche und Doppelatzen werden an Cu-Einkristallen niedriger Versetzungsdichte durchgefuhrt, um die Spannungsabhangigkeit des Losreisens eingewachsener Versetzungen im preyield-Bereich zu untersuchen. Eine geeignete Gluhbehandlung bringt die Proben jewils in ihren ursprunglichen Zustand zuruck, so das Experimente mit verschiedenen Versuchsparametern (Temperatur 77 und 300 K, Belastungszeit 6,7 ms bis 1 s, Verunreinigungsgehalt, Versetzungsdichte) verglichen werden konnen. Die Ergebnisse zeigen, das die charakteristische S-formige Spannungsabhangigikeit des Losreisens hauptsachlich bestimmt wird durch die Verteilung von Versetzungsbogenlangen zwischen Versetzungsknoten in hochreinen Proben und zwischen zusatzlichen Verunreinigungs-Clustern oder durch Verunreinigungen festgehaltenen jogs in weniger reinen Proben.

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.

Decoration of dislocations after neutron irradiation between 200° and 400°C

Abstract Copper crystals irradiated with neutrons at high temperatures show inhomogeneous clusters of damage. Etch pit studies of the low index planes reveal that the damage morphology is three dimensional and that the damage forms as a result of dislocation decoration.

The Elimination of Stacking Faults by Preoxidation Gettering of Silicon Wafers: III . Defect Etch Pit Correlation with p‐n Junction Leakage

Recently described procedures for the elimination of oxidation‐induced stacking faults have been incorporated into a device processing line to yield data on the leakage in p‐n junction tester diodes. The gettering processes, which take place on the back side of a wafer before the first oxidation, include the deliberate introduction of misfit dislocations and/or the deposition of a highly strained layer of . The results show that leakage currents can be reduced by several orders of magnitude and diode yields increased from about 10% to greater than 90%. By doing “post mortem” chemical etch pit studies on previously electrically mapped arrays of diodes the relative effectiveness of the two gettering schemes are compared. Factors such as the type of stacking fault, whether it be related to a native or process‐induced source, or whether it is clean or decorated are discussed as well as the influence of slip‐type dislocations.

The Characterization of Dislocations in Organic Molecular Crystals by Transmission Electron Microscopy

Abstract The role of transmission electron microscopy (TEM) for the characterization of dislocations in materials has been extensively described in the literature (see, for example, Hirsch et al.1 and references therein). Previous studies of defects in organic molecular crystals have utilized etch-pit studies, x-ray topography and simple microscopic deformation.2 It is the purpose of this paper to indicate how TEM serves as a valuable addition to this list of techniques.3