Burgers Vectors of Dislocations in Creep-deformed Fe3Si Single Crystals

In creep-deformed Fe₃Si single crystals the Burgers vectors of the dislocations were examined by transmission electron microscopy. The Burgers vector in a sample deformed under conditions of 60 MPa and 575–600 °C was of the type 1/2 〈110〉, whereas 〈111〉 superlattice dislocations were not found. 1/2 〈110〉 is the shortest translation distance in the D0₃ superlattice structure of Fe₃Si.     

Microstructure and strain relaxation of orthorhombic TmMnO3 epitaxial thin films

Orthorhombic TmMnO₃ (o-TMO) thin films have been epitaxially stabilized on (110) SrTiO₃ substrates by pulsed laser deposition (PLD) technique. The microstructure and strain relaxation mechanism of o-TMO thin films are analyzed using transmission electron microscopy. It is shown that major defects in the films are misfit dislocations with Burgers vectors of type a_p〈010〉 and a_p〈110〉, whereas a_p〈110〉 dislocations tend to dissociate into partial dislocations with Burgers vectors of type 1/2a_p〈110〉. Strain in o-TMO films is relaxed by misfit dislocations as well as surface fluctuations, which is different from most of the previous studies of the perovskite thin films.     

TEM-Untersuchungen von Gitterfehlern in ZnSiP2-Einkristallen

Results are dealt with concerning TEM investigations of lattice defects in ZnSiP₂ single crystals. After the crystal growth dislocations or stacking faults were found in a few cases only. More frequently twins were present in the microstructure. The crystallographic elements of twinning are {112} 〈111〉. After plastic deformation by bending at 900 °C local dislocation arrangements with high defect density (N_v ≈ 10⁶…︁ 10⁷ cm⁻²) were observed. By means of the diffraction contrast one Burgers vector b = 1/2 〈111〉 could be identified. In some cases the crystals also contained wide deformation stacking faults, which were limited by partial dislocations. The density of twins was not increased under the conditions of deformation reported here. As it can be concluded from investigations of Oettel et al. and from the results of the twin analysis, slip and generation of stacking faults take place on {112}-planes in ZnSiP₂ crystals. Crystallographic considerations on both processes are dealt with.     

Calculation of displacement fields and simulation of HRTEM images of dislocations in sphalerite type A(III)B(V) compound semiconductors

The displacement fields of different kinds of both perfect and dissociated dislocations have been calculated for an isotropic continuum, and by means of linear elasticity. Additionally, the corresponding HRTEM images have been simulated by the well-established EMS program package in order to predetermine the structural aspects of dislocations, and then to compare it with experimental HRTEM micrographs. The latter ones resulted from plastically deformed GaP single crystals and InAs/(001)GaAs single epitaxial layers. It could be established that using the simple approach of linear elasticity and isotropy results can be obtained which correspond well to the experimental images. So, the structure of various Shockley partial dislocations bounding a stacking fault can be detected unambiguously. The splitting behaviour of perfect 30° dislocations (separation into a 0° and 60° partial) and 90° dislocations (separation into two 60° partials) both with line direction along 〈112〉, 60° dislocations (separation into 30°/90° and 90°/30° configuration) and screw dislocations (separation into two 30° partials) along 〈110〉 are discussed in the more detail. Moreover, the undissociated sessile Lomer dislocation, glissile 60° dislocation and edge dislocation have been considered too.     

TEM and X-ray investigations of defect structure of PbSnTe crystal

The Pb_0.8Sn_0.2Te single crystal grown by the Bridgman technique was examined by X-ray and TEM methods. The X-ray reflection topography revealed that the PbSnTe crystal consisted of monocrystallinic blocks with linear dimensions of 1–5 mm separated by low angle boundaries of tilt-twist character. “As grown” defects observed by TEM method have been identified as single perfect dislocations and dislocation pairs. A mean density of dislocations inside the crystal blocks was no more than 10³ cm⁻². Except “as grown” defects rows of mobile dislocations were observed. All of dislocations lines were characterized by the same type of Burgers vector, i.e. b = 1/2a〈110〉.     

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.     

TEM Investigation of Dislocations in RNi2B2C (R = Y,Tb, Ho,Er, Y0.6Tb0.4, Er0.8Tb0.2)

To evaluate the influence of different rare earth metals on dislocation type and stacking fault occurrence in RNi2B2C compounds samples with R = Y, Tb, Ho, Er, Y_0.6Tb_0.4 and Er_0.8Tb_0.2 were investigated. As a result of the TEM analysis the parameter decisive for the lattice defects in these compounds is not the type of components but the annealing treatment of the samples. In well homogenized material the dominant Burgers vector of perfect dislocations was <100] and stacking faults are hardly found. In inhomogeneous samples the dominant Burgers vector was <110] and the perfect dislocations often lie in the planes of the numerous stacking faults. In both types of materials the experimental results hint at the existence of two different slip systems.     

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.     

Melt Growth of CdTe Crystals and Transmission Electron Microscopic Investigations of their Grain Boundaries

Transmission electron microscopy investigations are carried out on CdTe crystals grown in quartz ampoules in a temperature region (1020–1091 °C) near to the melting point of 1092 °C, by travelling heater method in quasi-closed and in sealed (at 0.135 Pa) volume, and by the Bridgman method from nearly stoichiometric melts. An original method for preparation of CdTe thin foil is reported. Two types of grain boundaries are observed: high-angle misoriented grain boundaries (more than ten degrees misorientation between adjacent grains) and low-angle misoriented grain boundaries (less than one degree misorientation between adjacent sub-grain). Both dislocations with Burgers vector b = a/6 〈112〉 and b = a/2 〈110〉 are present.     

Structural Defects in Type I Diamonds

Natural gem diamonds of Type I single crystals were observed with an ultra high voltage transmission electron microscope in order to characterize structural defects such as dislocation, dislocation loops, and platelets. The results of analyses indicated that edge dislocations with Burgers vector 1/2 [011 1] and 60° dislocations which were inclined at an angle of 60° to 〈011〉 directions were present in the diamonds. Dislocation loops were concluded to be in interstitical character. It was speculated that an impurity associated with the platelets was silicon and dislocation loops were formed by dislocation motion.     

Defects in implanted and Czochralski silicon

Rod-like defects, a6〈114〉 and a/3〈111〉 faults, and a/2〈110〉 loops may all be generated by self-interstitial aggregation during the annealing of implanted or Czochralski silicon, and several models, intended to account for one or more of these, are compared. It is concluded that the rod-like defects are {113} faults, and that the three faulted defects form independently (i.e. they are not related in an „evolutionary”︁ sequence). The dipolelike a/2〈110〉 loops probably result from the unfaulting of {113} faults, while other perfect loops are generated by the shear of a/6〈114〉 defects. At a given temperature, the latter appear considerably more likely to unfault than the a3〈111〉 faults. The structure of the {113} fault remains uncertain.     

Electron microscopy analysis of dislocation behavior in HVPE-AlGaN layer grown on a stripe-patterned (0 0 0 1) sapphire substrate

Microstructures were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in order to clarify the dislocation behavior in AlGaN layers HVPE-grown on a stripe-patterned sapphire (0 0 0 1) substrate. SEM observation revealed very clearly the growth process: if AlGaN starting to grow from the side-wall of patterned substrate develops, a poly-crystalline region is formed up to the top surface of thin film. When the growth from the upper side (terrace) of patterned substrate is predominant, AlGaN becomes a single-crystalline layer with a flat surface. Threading dislocations (TDs) generated from the interface to the terrace propagate upwards, inclining to the wing regions. They are scarcely merged with one another. The AlGaN layer on the patterned substrate with a wider groove has a smaller density of dislocation to be about 1×10⁹ cm⁻². There are four types of dislocations: (1) TDs inclining toward 〈1 1¯ 0 0〉 normal to their Burgers vector B; (2) TDs inclining toward 〈2 1¯ 1¯ 0〉 on their slip-plane; (3) TDs inclining largely or horizontal dislocations (HDs) along 〈2 1¯ 1¯ 0〉 and (4) roundly curved HDs lying on (0 0 0 1) plane. Some TDs change the direction of inclination, suggesting that internal stress changed intricately during the growth.     

Stacking faults in semi‐polar 6H‐SiC single crystals

6H‐SiC single crystals have been successfully grown on (1015) plane seed by sublimation method. High density stacking faults (SFs) were observed by transmission synchrotron radiation X‐ray topography. Based on the invisibility criteria of stacking faults, the displacement vectors of most SFs were determined to be the type of 1/6[1120]. Laser scanning confocal microscopy (LSCM) was used to observe the etching morphology of (0115) wafer. The etching steps of SFs were found and their density decreased from 3.6×10³ cm^‐1 to 2.0×10² cm^‐1 along the <0001> projection direction. The inclination angles of the SFs etching step plane to (10‐15) plane were measured by line scanning of LSCM. It was found that the inclination angles decreased from 20° to 10° along the <0001> projection direction. Different etching characteristics of SFs along radial direction of 6H‐SiC (1015) wafer should be attributed to different displacement vectors and different stacking fault energies for these stacking faults. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reflection Splitting in RHEED Investigations of Vacuum Evaporated GaAs Layers

RHEED-diagrams of vacuum deposited GaAs-films with high density of structural defects often show splitting of matrix reflections into satellites. It can be shown by simple models, for example of {111}-oriented films, that this phenomenon is originated by formation of stacking faults perpendicular to 〈ĪĪĪ〉-B growth directions of the films. The conditions for 〈110〉 and 〈211〉 azimuths are discussed.     

Evaporation Model of NaCl Cleavage Faces around Edge Dislocations in Vacuum

It is shown in the present paper that the evaporation of edge dislocations in the form of circular steps takes place in NaCl crystals by the evaporation of these steps in a high vacuum and in a temperature region of 350–500°C. The distances of steps are regular. This regularity is explained by means of a suggested model. This model explains also the change in the evaporation rate depending upon the density of dislocations. This explanation is based on the existence of an effective charge at the emergence point of the edge dislocations a/2 〈110〉. {110} with the surface planes {100}. This charge interacts with another one formed on the faults of steps. As a result of this interaction a modulation is observed of the formation of a new step in the emergence point. This means that the same is observed in the case of step distances too.     

Characterization of crystal defects in mixed tabular silver halide grains by conventional transmission electron microscopy and X-ray diffractometry

Tabular silver bromide grains with iodide uniformly mixed in the shell were investigated with conventional transmission electron microscopy. The shell region was found to contain a large number of stacking faults parallel with the {11 } edges and in some cases edge dislocations with a Burgers vector of type. An atomic model for the formation of the stacking faults during the growth is presented.     

Morphology and orientation relations of BaCl2 precipitates in NaCl single crystals

In the present paper morphology and orientation relations of BaCl₂ precipitates in NaCl single crystals are described. It is shown that BaCl₂ precipitates of large dimensions are formed at the dislocations of a/2〈110〉{100}, the dislocation lines of which are oriented in the directions 〈210〉.     

Dislocations and dislocation reduction in space grown GaSb

The behaviour of dislocations in GaSb crystals grown in space both from a stoichiometric melt (floating zone method, FZ) and a Bi solution (floating solution zone, FSZ) respectively, is studied. Predominantly straight 60° dislocations with Burgers vectors of the type b = a/2 <110> in (111) glide planes are identified. In the 20 mm long FZ single crystal the linear growing out of the dislocations is observed which reduces the dislocation density in the centre of the crystal to values below 300 cm^–2. The Bi incorporation in the FSZ crystal results in a misfit between seed and grown crystal and in a network of misfit dislocations at the interface. Thermocapillary convection during growth as well as the surface tension may be the reasons for the presence of curved dislocations and the higher dislocation density within a 1 – 2 mm border region at the edges of both of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the question of symmetry classification of ordered tetrahedrally coordinated structures

Substructures of tetrahedrally coordinated polytopes (4D polyhedra) are determined as “polytopes” {136} and {408}, which are divided into nonintersecting 17-vertex aggregations of four centered tetrahedra. It is shown that 17-vertex polyhedra of the diamond structure and polytopes 〈136〉, {240}, 〈408〉, and {5, 3, 3} differ only by the angle of synchronous rotation of external vertex triads, and the cell of each structure is determined by the two nearest nonintersecting 17-vertex polyhedra. The following sequence is proposed as a basis for symmetry classification of ordered tetrahedrally coordinated structures: diamond structure 〈136〉 {240} → 〈408〉 → {5, 3, 3}. The possibilities of the developed approach are demonstrated by the example of constructing a rod with the screw axis 8₂ from cells of the polytope 〈136〉; this rod can be transformed into a diamond substructure: a helicoid of diamond parallelohedra with the screw axis 4₁.     

Stacking faults in deformed zinc and magnesium single crystals

Using the transmission electron microscopy dissociated dislocations containing stacking faults were observed in Mg single crystals, deformed in (0001) <1120> slip system, and in Zn single crystals deformed in {1122} <1123> slip system. The overlapping flat stacking faults lying in {1102} planes and dissociated triple nodes in (0001) planes are observed in Mg. In Zn flat stacking faults are found in {112 2} planes. The value of stacking fault energy γ has been determined in Mg crystals (γ ⋍ 10 erg/cm²). Such a low value of γ is attributed to the segregation of impurities on dislocations.