Stability of dislocations in MgO single crystals at high temperatures

The dislocation structures of MgO single crystals annealed at 1900 °C for 3 hrs and at 2000°C for 1 hr were observed electron microscopically, and it was found that the following reactions took place at high temperatures: a/2 〈11 0〉 + a/2 [110], = a [100], a/2 [110] + a/2 〈11 01〉 = a/2 [011]. The resultant dislocations were sessile. Their interaction with impurities would make the subgrain boundaries stable.     

Characterization of dislocations in a LiNbO3 single crystal grown by micro pulling down method

LiNbO₃ single crystals grown by the micro pulling down (μ-PD) method have been revealed to be as free of dislocations and subgrain boundaries up to 500 μm in diameter. On the other hand, μ-PD LiNbO₃ single crystals grown along the x-axis in diameter of 800 μm were observed to be dislocated due to the size effect of crystal. The Burgers vectors of dislocations were determined to be [22 01], [101 1], and [01 11] by X-ray topography.     

Geometrical properties of dislocations in potassium bichromate crystals

The geometry of growth dislocations present in potassium bichromate crystals grown from aqueous solution has been studied by etching. Etch topographs composed of dislocation etch grooves and grooves representing sector boundaries and growth bands have been analysed. It was found that most of the dislocation lines are straight and have well-defined directions in each sector. Refractions of dislocations at growth sector boundaries and at other defects have been observed.     

Growth dislocations in zonal isomorphously mixed crystals

The orientation, distribution, and density of dislocations in isomorphously mixed potassium-rubidium biphthalate crystals composed of two zones with different concentrations of isomorphous rubidium impurity are experimentally studied. A model for the formation of growth dislocations in the external zone, which compensate internal heterometry-induced stresses at the interface between the zones, is proposed.     

Diffusion of self-point defects in body-centered cubic iron crystal containing dislocations

The energetic, crystallographic, and diffusion characteristics of self-point defects (SPDs) (vacancies and self-interstitial atoms (SIAs)) in body-centered cubic (bcc) iron crystal in the absence of stress fields have been obtained by the molecular statics and molecular dynamics methods. The effect of elastic stress fields of dislocations on the characteristics of SPDs (elastic dipoles) has been calculated by the methods of the anisotropic linear theory of elasticity. The SPD diffusion in the elastic fields of edge and screw dislocations (with Burgers vectors 1/2 〈111〉 and 〈100〉) at 293 K has been studied by the kinetic Monte Carlo method. The values of the SPD sink strength of dislocations of different types are obtained. Dislocations are more effective sinks for SIAs than for vacancies. The difference in the sink strengths for SIAs and vacancies in the case of edge dislocations is larger than the screw dislocations.     

Electron-carrier generation by edge dislocations in InN films: First-principles study

Electronic structures of edge dislocations in InN films are studied using the first-principles calculation. We found that dangling-bond states of In atoms localized in the dislocation core are located above the conduction-band bottom and thus supplies the electron carriers to the conduction band of bulk InN, in agreement with the experimental suggestion by Wang et al. [Appl. Phys. Lett. 90 (2007) 151901]. Moreover, it is shown that the Fermi energy in the conduction band has the tendency to be pinned at the energy positions of N-related dangling-bond states.     

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.     

Nature,origin and effect of dislocations in epitaxial semiconductor layers

The paper is concerned with the manner in which dislocations in Group 3–5 compound epitaxial layer structures are generated, propagate and interact with one another. The different types of epitaxial layer and dislocation behaviour are initially reviewed. The examination methods used are based on electron microscopy. The TEM is used in conjunction with plan-view, cross-section, and angle-lap specimens to determine the detailed nature and three-dimensional distribution of the dislocations. The SEM EBIC and CL methods are used with bulk specimens to obtain electrical and luminescent information. In particular, the latter methods give micrograph-type images showing dark spots and lines corresponding to individual dislocations, the contrast arising because of electrical carrier recombination taking place at the dislocations. These methods are used to investigate the dislocation behaviours occurring in a wide range of specimens including homo- and hetero-epitaxial layers, and embracing small, medium and large mismatches. An attempt is made to obtain quantitative data concerning the processes occurring. The work has provided a better understanding in many instances, and sometimes allowed the occurrence of the dislocations to be better controlled. An example is given of the application of the results to the improvement in the quality of a GaAs transmission photocathode device-type structure.     

On crack nucleation in zinc upon interaction of basal and pyramidal dislocations

The interaction of intersecting basal and pyramidal dislocation pileups in single-crystal zinc has been analyzed. Different versions of the formation of sessile (1/3[4 $ \bar 2\bar 2 $ 3]) and cleavage ([0001]) dislocations (microcrack nuclei) are considered. The merging of the head dislocations in pyramidal pileups is shown to be preferred. The conditions for thermally activated dislocation merging are derived. The conditions for crack opening according to the Gilman-Rozhanski? mechanism are discussed. It is analytically established that the breaking stress, normal to the (0001) plane in the region of microcrack nucleation, exceeds the theoretical strength.     

Electrons,dislocations, and low-temperature plastic deformation

The influence of electron drag processes on the plasticity of normal state metals is demonstrated in the case of zinc crystals. These results show that dislocations move as underdamped oscillators at low temperature and that dislocations flutters as they move. This flutter motion, in contrast to kink motion which is expected to have no long range stress, is the dominant drag process at temperatures below ≈ 4.2 K.     

Infrared light scattering and absorption microscopy investigations at dislocations in GaAs crystals

In recent years a number of experiments have been published dealing with the light scattering at small particles. All of these experiments have been made in the visible spectral range. In this paper we report an experimental arrangement for infrared light scattering by dark-field illumination. Preliminary results of the observations of dislocations in GaAs crystals are given. The scattering images are correlated with results obtained by means of absorption microscopy with infrared light. Helix-like fine structures of dislocations are found mainly arranged in the 〈110〉 directions.     

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.     

Energy levels of dislocations in Ge under different conditions. Comparison between images of electron- and light-beam scanning microscopy

Thermal treatment effects on Ge deformed at 350°C are consistent with reductions of the effective dangling bond densities on the dislocations. On account of difficulties in the application of known statistics the phenomena observed are briefly discussed by considering a heavily doped cylinder model for the dislocations. Observations with infrared beam induced currents emphasize the necessity of considering the effects of other defects, introduced together with dislocations during deformation, in particular for the interpretation of photoconductivity data.     

Antistructure disorder and its relation to dislocations in III–V semiconductors

Intimate relationship between antistructure defects and dislocations occurs in GaAs which manifests itself as: (i) appearing of spatial correlation between grown-in dislocations and the EL2 defects (component of the latter are As_Ga antisites), (ii) similar suppression of the concentration of EL2 and dislocation density due to the doping with donor impurities, (iii) generation of As_Ga antisites during the plastic deformation of a crystal. Al these effects can be understood in terms of the dislocation-mediated generation of As_Ga antisites via absorption of As_i interstitials at dislocation jogs. Large anion (cation) precipitates appearing at dislocations are pointed out to be important for both antisite and dislocation generation under certain conditions.     

Formation of dislocations in Sb crystals grown by pulling from melts

Results of experimental investigations on regularities of the formation of dislocations in crystals of pure antimony during pulling from melts are reported. The mean density of dislocations is compared with the values calculated by different theories.     

Study of imperfections in iron whiskers

Iron whiskers grown by hydrogen reduction of ferrous chloride were studied by several X-ray and optical techniques, particularly by X-ray diffraction topography. 36 whiskers with [100], [110] and [111] axis directions, from 20 μm to 260 μm in thickness were investigated. They were of different degree of perfection with dislocations nonuniformly distributed. Three [111] whiskers showed a lattice twist around the axis. Burgers vectors of several frequent types of dislocations were found.     

Lattice strain and misfit dislocations in GaAs-GaAlAsP heterojunctions

The lattice strain and misfit dislocations in a GaAs-GaAlAsP heterojunction were examined. The change in lattice strain with the composition ratio or the position of the crystal was measured, and it was found that some of the misfit dislocations introduced in the heterojunction were edge-type dislocations. The critical thickness of the epitaxial layer for the generation of misfit dislocations was also measured. The critical differential strain between the atomic layers was on the order of several angstroms. The distribution of lattice strain was analyzed by a two-dimensional simple cubic lattice model, and the distribution of differential strain was examined.     

Dislocations of salol crystals grown by the Czochralski method

Crystals of salol were grown by the Czochralski method in three different pulling directions to examine the crystallographic orientation effect of the seed. They were characterized by the etch pit method and X-ray projection topography. It was found that the dislocation density was 2 × 10³−1 × 10⁴/cm² and that the configuration of dislocations was straight. The running directions of dislocations strongly depend on the pulling directions; i.e., [11 0] and [1 10] for the crystal grown in [100] axis, [11 0], [1 10] and [110] for the crystal pulled along [112] axis and [010] for [010] axis crystal.     

Dynamic interaction of dislocations with impurity subsystem in crystalline materials

The entrainment of impurities by moving dislocations results in the accumulation of impurities in dislocation cores, which eventually significantly modifies the dynamic properties of dislocations. In the framework of the kink mechanism, the possible modes of motion are found self-consistently and the conditions for dislocation immobilization are determined. The dependence of the immobilization stress (the parameter that is most important for ??defect engineering?? in semiconductors) on the material parameters and experimental conditions is calculated.     

Propagation behavior of threading dislocations during physical vapor transport growth of silicon carbide (SiC) single crystals

The dislocation formation and propagation processes in physical vapor transport (PVT) grown 4H silicon carbide (4H–SiC) single crystals have been investigated using defect selective etching and transmission electron microscopy (TEM). It was found that while the growth initiation process generally increased the density of threading dislocations in the grown crystal, for certain areas of the crystal, threading dislocations were terminated at the growth initiation. Foreign polytype inclusions also introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, almost no medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the foreign polytype inclusions had ceased the propagation of threading screw dislocations. Based on these results, we argued the formation and propagation of the threading dislocations in PVT grown SiC crystals, and proposed the dislocation conversion process as a plausible cause of the density reduction of threading dislocations during the PVT growth of SiC single crystals.