Dislocation studies by chemical etching on solution-grown NaSbF4 and Na3Sb4F15 single crystals

An attempt has been made to study the etch pit dislocations of isolated as well as matched pairs of cleavage planes of solution grown NaSbF₄ and Na₃Sb₄F₁₅ single crystals when etched with analar grade methyl alcohol and ethyl alcohol. On etching of cleavage faces the pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, arrays of triangular shape etch pits are observed. After prolonged etching some of the etch pits disappear. These pits are curved and terminated indicating that they are crystallographically non-oriented. One-to-one correspondence with respect to number, shape, position and structure of the pits has been established by etching of a matched cleavage face. The etch pit densities of both NaSbF₄ and Na₃Sb₄F₁₅ crystals are found to be 10³ per cm².     

Dislocation etching of tin iodide single crystals

Single crystals of tin-iodide (SnI₂) have been grown using the controlled reaction between SnCl₂ and KI by diffusion process in gel medium. As grown (010) surfaces of the crystals have been optically studied. Characteristic etch pits have been observed on them. This suggests that SnI₂ crystals might go into dissolution in the acid-set gel. By successively etching (010) surfaces in a mixture of ammonia, acetic acid, and CdCl₂ solution, it is established that the pits indicate the site of dislocations in the crystals. This is further confirmed by comparing the etch patterns before and after chemically polishing (010) surfaces. The average dislocation density in the crystals have been evaluated and found to be 3.2 × 10³ cm⁻² and the implications are discussed.     

Dislocation activity in single crystals of stannic iodide

Single crystals of stannic iodide (SnI₄) have been grown employing the controlled-reaction between SnCl₂ and KI solutions by diffusion process in silica gels. As-grown (111) surfaces of the crystals have been optically studied. Characteristic growth spirals and hopper growth patterns have been observed on them. By successively etching (111) surfaces in a 0.2 N HCl solution, it is established that the pits indicate the sites of dislocations in the crystals. This is further confirmed by comparing the etch patterns before and after chemically polishing (111) surfaces. The average dislocation in the SnI₄ crystals have been determined and found to be 7.3 × 10² cm⁻². Observations of polygonisations are described and the implications are discussed.     

Etch- and Transmission Electron Microscope Investigations of Microdefects in (001) LEC-GaP Substrates

The etch pattern of (001) and (110) LEC-GaP doped with sulphur (N_DN_A in the range from 3–7 × 10¹⁷ cm⁻³) do not only show dislocation etch pits but fine pits, so-called “saucer pits” (S-pits). The distribution of S-pits, their etching behaviour and transmission electron microscope observations of etched samples indicated a clear correlation between S-pits and microdefects (fauted-, prismatic dislocation loops and precipitates).     

Effect of dislocation loops in macroscopically dislocation-free GaP substrates on the perfection of homo-epitactic deposits

Substrates and epitactic layers of GaP are etched under optimized conditions with the defect-revealing, preferential R-C etchant and subsequently examined using high-magnification (about 2500X) optical microscopy techniques. It is possible then to distinguish two new phenomena, viz. etch pits characteristic of dislocation loops in the substrate, and inclined dislocation dipoles in the layer. For layers grown on dislocation-free substrates we find that (i) the surface densities of both defects are equal (～5 × 10⁵cm^-2), and (ii) the average diameter of the dislocation loops in the substrate is roughly the same as the average distance between the two dislocations of the dislocation dipoles (0.5?1μm). Hence the perfection of these layers is determined by interfacial dislocation loops. Because the density of dislocation loops is only about a factor of two lower in highly (～1 × 10⁵ cm^-2) dislocated substrates, growth on these substrates results in layers which have even slightly lower dislocation density than layers grown on dislocation-free substrates. In the former case also single dislocations in the substrate propagate into the layer. Minority-carrier lifetime data indicate that minority-carrier recombination at dislocations is a restrictive factor for the luminescence quality of layers grown both on dislocation-free and highly-dislocated substrates.     

Tracing of dislocations in ammonium hydrogen tartrate single crystals

Sparingly soluble ammonium hydrogen tartrate (AHT) crystals are grown by the gel method, derived from the diffusion of ammonium chloride into the set gel containing tartaric acid. Crystals up to 23 × 5 × 3 mm³ in size are grown at room temperature. AHT crystals are cleaved along (010) planes and the cleavage surfaces are studied by using multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. An attempt is made to trace the trajectory of dislocations of isolated as well as matched pairs of (010) cleavages of AHT when etched in a mixture of formic acid and methyl alcohol (2:1) and 1.0 M SrCl₂ solutions. Optical and transmission electron micrographs of dislocations show oblique, parallel and continuous line characteristics. Rows of equally spaced dislocation pits are observed and the implications of this are discussed.     

Structural Etching of {001} and {110} Faces of Various AIIIBV Compounds

The present paper discusses the use of selective photoetching with H₃PO₄:H₂O₂ for characterizing various A^IIIB^V compounds and detecting misfit dislocations in transition layers. For GaP, the results obtained are compared with those realized with the use of an AB etchant for which suitable conditions for the structural etching of {001} material and the characterization of cleavage faces are given. The direction of the dislocation line is inferred from the shape and orientation of etch pits. The etch figures of different types of misfit dislocations are discussed.     

Plastische Verformung von Siliziumeinkristallen unterschiedlicher Ausgangsversetzungsdichte im Streckgrenzenbereich

Floating-zoned Silicon crystals orientated for single slip both dislocation-free and with grown-in dislocations (EPD₀ = 6,5 · 10⁴ cm⁻²) were dynamically deformed in compression in the temperature range 1120 … 1300 K up to the lower yield point. The dislocation structure of plastically deformed crystals (T = 1138 K; a₀ = 1,45 · 10⁻⁴ s⁻¹) was examined by etching and high-voltage electron microscopy. The crystals exhibit essential differences in deformation behaviour and in the resulting dislocation structure. Typical for the dislocation-free basic material are (i) an inhomogeneous deformation in the range of the upper yield point (ii) a greater portion of sessile lomer dislocations at the lower yield point in relation to the crystal with grown-in dislocations. The measured stresses were related to those values calculated from structure data by employing plasticity theory of diamond-like semiconductors.     

Efficiency of dislocations as sinks of radiation defects in fcc copper crystal

The sink efficiency of perfect dislocations for self-point defects (interstitials and vacancies) in fcc copper crystal has been calculated by the kinetic Monte Carlo method in a temperature range of 293–1000 K and a range of dislocation densities from 1.3 × 10¹² to 3.0 × 10¹⁴ m^?2. Screw, mixed, and edge dislocations with a Burgers vector 1/2<110> in different slip systems are analyzed. The interaction energies of self-point defects with dislocations are calculated using the anisotropic theory of elasticity. Analytical expressions are proposed for the dependences of the calculated values of dislocation sink efficiency on temperature and dislocation density.     

Etching of CaF2 single crystals in silica gels

Etching of {111} cleavage faces of CaF₂ crystals in aqueous solution of 50% HCl is carried out in citric acid set silica gel, and the kinetics of growth of etch pits at the sites of dislocations is investigated as a function of temperature, time of etching and height of gel column above the crystal surface. It is observed that the transient period required to initiate etch pit at the sites of a dislocation decreases (1) at particular temperature, with a decrease in gel height, and (2) for a particular gel height, with an increase in the temperature of etching. It is also observed that the morphology of dislocation etch pits remains triangular irrespective of the gel height and the temperature of etching. The results are compared with those of solution etching and discussed.     

Zum Nachweis von Versetzungen in β-Kupferphthalocyanin-Einkristallen

An etching technique was developed to investigate dislocations in β-copper phthalocyanine single crystals. Considering the expected content of dislocations and the etch pit symmetry the symmetric etch pits are correlated to [010]-edge dislocations on {201 }- and {001}-lattice planes with (001)- and (201 )-slip planes. Asymmetric etch pits on {001}- and {201 }-planes are connected with [010]-edge dislocations related to (100)- and (101 )-slip planes. The dislocation density on growth planes and cleavage planes is commonly lower than 100 cm⁻². [010]-screw dislocations are not observed, but their existence could not be excluded.     

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.     

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.     

Ätzuntersuchungen an Verneuilspinellen

The quality of (100), (110), and (111) oriented spinel substrates in the composition range MgO × 3.3-3.5 Al₂O₃ is examined by chemical etching. The investigation shows that KHSO₄, H₃PO₄, and Na₂B₄O₇ cause dislocation etch pits on (111), and only KHSO₄ on (100) faces. The little rod-shaped defects revealed by etching on (100), (110), and (111) faces were found to be Al₂O₃ precipitates.     

X-ray diffraction study and quantitative measurements of high dislocation densities in superlattices and single crystal layers of heteroepitaxial systems with pronounced lattice mismatch

Plastic deformation in a single-crystal layer of the In_0.12Ga_0.88As/(111)InP solid solution is identified by the methods of X-ray diffractometry (XRD) and the double-crystal pseudorocking curves (DCPRC). X-ray topographs showed the generation of three intersecting systems of straight dislocations in the layer. In a one-layer ZnSe/GaAs structure and multilayer ZnSe/ZnSe_{1 − x} S_x/ZnSe/GaAs structures, the elastic and plastic strains were detected by the combined XRD-DCPRC method. The major components of the thermoelastic and plastic-deformation tensors were determined as ε_xx = ε_yy = 3.5 × 10⁻³ and ε_zz = 2.35 × 10⁻³. Using these data, the dislocation densities were determined as N _d ∼ 2.5 × 10⁸ cm⁻² and N _d ∼ 3 × 10¹⁰ cm⁻² for the 7 μm-thick ZnSe and 1 μm-thick InAs layers, respectively. In a superlattice of the Al_xGa_{1 − x} As/GaAs/⋯/GaAs-type with a large lattice parameter, the plastic deformation was detected. X-ray topography confirmed that the dislocation density in this superlattice equals ∼10⁵ cm⁻². __________ Translated from Kristallografiya, Vol. 45, No. 2, 2000, pp. 326–331. Original Russian Text Copyright ? 2000 by Kuznetsov.     

Growth,etching morphology and spectra of LiAlO2 crystal

γ‐LiAlO₂ single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X‐ray rocking curve and chemical etching. The effects of air‐annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO₂ were also investigated in detail. The results show that the as‐grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7‐22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×10³ cm^–2. The VTE‐treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air‐annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dependence of positron capture rate on dislocation density in solid solutions of KCl—KBr

Generally well-annealed alkali halide crystals exhibit three lifetime components. τ₁ arises due to annihilation with anion and τ₂ due to Bloch Ps. The origin of τ₃ is not well understood. Positron lifetime and etching techniques have been performed on solid solutions of KCl_100−xBr_x with mole % of x = 0.0, 15, 30, 37, 50, 70, and 100. The positron lifetime spectra have been analysed to resolve into three components. The positron capture rate K₃ for the longest lived component and the dislocation density shows a non-linear variation with composition. The positron capture rate varies linearly with the dislocation density of the samples. The origin of τ₃ is identified as due to positronium formation in the dislocations present in the samples. The trapping probability per dislocation has been estimated to be 2.2 × 10⁻¹²/s.     

Influence of Microdefects on the Generation of Dislocations in Homoepitaxial Gallium Phosphide Layers Grown on LEC Substrates

GaP LEC substrates doped with sulphur (N_D – N_A roughly (3–7) × 10¹⁷ cm⁻³) were characterized by transmission electron microscopy. This material was found to contain microdefects such as perfect perismatic dislocation loops, and spherical precipitates. Cross-sectional TEM investigations perfomed have shown that above all perfect dislocation loops lying directly at the substrate/layer interface are sources for the formation of extended dislocations propagating through the epitaxial layer. Using the methods of selective photoetching and AB-etching on (110) cleavage faces this phenomenon was observed, too.     

Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

Single crystals of Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 10⁴ to 10⁵ /cm². Microhardness studies are made on as–grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman–Chin parameter H_v/C₄₄, where H_v is the microhardness and C₄₄ is the shear constant. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.