Kinds Of Dislocations Research Articles

Crack-free GaAs epitaxy on Si by using midpatterned growth: Application to Si-based wavelength-selective photodetector

A monolithically integrated wavelength-selective photodetector, which consists of an 11.86 μm thick GaAs-based Fabry–Pérot filter and a 3.84 μm thick InP-based p-i-n absorption structure (with a 0.3 μm In0.53Ga0.47As absorption layer), was grown on a Si substrate. A crack-free and high-quality epilayer with an area of 800×700 μm2 was obtained by using midpatterned growth and thermal-cycle annealing. Long dislocations running parallel to the GaAs/Si interface were formed by thermal annealing. This kind of dislocation may effectively alleviate the thermal stress across a large patterned area and be responsible for the crack-free epilayer. A photodetector with a spectral linewidth of 1.1 nm (full width at half maximum) and a quantum efficiency of 9.0% was demonstrated.

A cohesive zone model based on the micromechanics of dislocations

The deformation in the vicinity of a crack tip is governed by the presence of plastic strains and plastic strain gradients. Statistically stored and geometrically necessary dislocations related to these measures of deformation play a vital role in fatigue crack growth of metals. Both kinds of dislocation are responsible for crack advance as well as for crack tip shielding. We introduce a novel cohesive zone model for the description of fatigue crack growth in metals. The model incorporates the stress fields due to dislocations into the constitutive model of the cohesive zone. While the plastic deformation characteristics are calculated using a finite element model, the stress at the crack tip due to multitudes of dislocations are expressed by analytical expressions which are derived from the stress field of an individual dislocation. The cohesive strength is overcome due to a combination of stresses arising from material separation enhanced by the stresses due to the dislocations. Crack growth for constant amplitude loading and the overload case is computed. The computed dislocation densities are similar to those obtained by discrete dislocation simulations. Significant crack closure is observed. A fatigue crack growth threshold and Paris law dependence of the fatigue crack growth rate on ΔK are outcomes of the model. Overload is discussed with respect to the dislocation density distribution and the resulting fatigue crack growth retardation. These results compare well with experimental findings of fcc metals.

Study on interface guided mode of 2D heterostructures dislocation defect phononic crystal

The effect on the guided modes in the gaps of the 2D mercury/water squared phononic crystal (PC) heterostructures dislocation, with the two kinds of dislocation, is studied with the plane-wave and the super cell methods. The results show that for the prototype heterostructure, there are no interface guided modes in the gaps, while the transverse, longitudinal dislocation can generate guided modes at the interface, which allow the sonic wave in the frequency range of the forbidden ones to transport along the dislocation channel and thus make the PC a sonic wave guide.

Electron-beam-induced current study of electrical activity of dislocations in 4H–SiC homoeptaxial film

The types of dislocations and their electrical activity in 4H–SiC homoepitaxial film were characterized by molten KOH etching and electron-beam-induced current (EBIC) method. Chemical etching has revealed that there exists four kinds of dislocations, namely basal plane, screw, edge-I and edge-II dislocations. EBIC image has indicated that they are electrically active at room temperature, and the EBIC contrasts of such dislocations are stronger in the order of basal > screw > edge-I > edge-II. Their EBIC contrasts gradually decrease by cooling, which is different from those of clean dislocations in Si, suggesting that the dislocations are accompanied with deep levels. Secondary electron images of etch pits show that the sizes for screw and edge dislocations have the sequence of screw > edge-I > edge-II, suggesting their Burgers vectors decrease in this order. The EBIC contrasts of these dislocations are discussed in relation to their Burgers vectors.

DISLOCATION DENSITY IN SrTiO3 FILM GROWN ON DyScO3 BY PULSE LASER ABLATION

SrTiO 3 films are fabricated on DyScO 3 substrates by pulse laser deposition. In situ X-ray diffraction (XRD) is used to characterize the thermal expansion coefficient at low temperature. The abnormal behavior in lattice parameter at 80 K may be the hint of a phase transition. High resolution XRD is performed to detect the two kinds of dislocations, i.e. screw and edge. Results show that the density of edge dislocation is a little larger than that of the screw one. The total dislocation density has the order of about 108 cm-2. Edge dislocation density decreases with the increase of the film thickness. We argue that the ratio between these two dislocation densities results in the growth mode of the film.

Indentation response of single-crystalline GaAs in the nano-, micro-, and macroregime

Abstract Fabrication, handling and processing of wafers of intrinsically brittle and anisotropic single-crystalline GaAs require a high level of control of the material's response to different loading conditions. The present work is focused on the response to hardness indentation. A short overview on the behaviour of (100) GaAs wafers in several doping conditions over a wide range of indentation loads from nano-indentation up to macro-indentation including sharp and blunt indenters is given. Special attention is paid to the pop-in effect in depth-sensing nano-indentation, to the anisotropy of indentation-induced radial crack formation and to the material's crack resistance obtained from the indentation fracture mechanics approach. We have observed that, under certain conditions, the frequency of formation of radial cracks is essentially different for the two in-plane <110> directions. This observation is attributed to the occurrence of two different kinds of dislocations and to the lack of inversion symmetry. The effect turns out to be closely related to a left – right asymmetry in the material removal caused by wire sawing. This insight has paved the way to the optimisation of the process of wire sawing of GaAs single crystals.

Evolution of microstructure and thermomechanical properties during superelastic compression cycling in Cu–Al–Ni single crystals

The aim of this work is to relate the macroscopic evolution of the compression superelastic effect in Cu–Al–Ni shape memory alloy single crystals with the evolution of the microstructure during cycling. The analysis has been carried out as a function of the number of cycles, the maximum reached deformation and the kind of induced martensite. Moreover, the new microstructure after mechanical cycling and the evolution of the thermal transformation have been also studied. The presence of two new families of dislocations created by different mechanisms has been observed and the influence of each one on the stress-induced and thermal transformations has been analyzed. In the samples where both kinds of dislocations are present at the same time, the observed behaviour is a combination of their effects in proportion to their density.

DIAGNOSTICS AND TERMINOLOGY OF RARE KINDS OF TRAUMATIC DISLOCATION OF SHIN

For the first time previously unknown three kinds of traumatic dislocation of shin has been described (floating knee-joint, floating hip, latent shin dislocation), and little-known four kinds of dislocation, - recurrent, habitual, angular, posttraumatic primary-chronic (previously described by the author for the first time) and rare voluntary shin dislocation which develops after traumatic. Terminology, diagnostics and outcomes are described. The general clinical material - 228 patients.

Dislocation-free CZ-Si crystal growth without the thin Dash-neck

It is found that dislocation-free Si crystal growth is possible without a thin neck. Dislocation behaviour in a heavily B-doped CZ-Si crystal has been analysed, and it is found that three kinds of dislocations generated due to thermal shock, lattice misfit and incomplete seeding must be suppressed to grow dislocation-free crystal without the thin Dash-neck. Heavily B-doped or Ge-doped Si seeds are useful in suppressing dislocation generation due to thermal shock, and heavily B- and Ge-codoped Si seeds not only suppress dislocation generation due to thermal shock most effectively but can also suppress that due to lattice misfit. A relative higher melt temperature at the start of pulling is suggested for suppressing the dislocation generation due to incomplete seeding. Dislocations were observed in crystals grown from an annealed heavily B-doped Si seed, and they were probably induced by the dislocation loops in the annealed seed.

Accommodation of the Lattice Mismatch at the VCx-WC Interface

A VC doped WC-Co alloy is investigated using high resolution transmission electron microscopy. The VC grain growth inhibitor induces the presence of a thin layer on the surfaces of the WC grains in contact with Co and precipitates in the corners of Co pockets. These (VW)Cx compounds adopt an epitaxial orientation relationship with regards to the (0001) base facets of the WC crystals. Due to the small difference in lattice parameters, misfit dislocations are expected in the interfaces. Unlike the thin layers where no defects are observed, two kinds of dislocations are pointed out for larger precipitates. 1/6〈112〉VC interfacial dislocations are sometimes present while more often 1/2〈1¯10〉VC dislocations lying above the interface in the (VW)Cx phase are visible.

Measurement of lattice displacements at planar defects in 2H and 18R martensites.

A review of transmission electron microscopy studies of planar defects in 18R and 2H martensites in Cu-Zn-Al alloys is presented. The non-basal plane faults observed in the 2H structure, the F1 faults, show two kinds of dislocations at their ends. In contrast, two types of non-basal plane faults are observed in the 18R structure, Fo and Fx faults. The non-basal plane faults can be composed of segments of Fo and Fx faults. Six types of imperfect dislocations appear, depending on the type of basal plane fault ending at the non-basal plane fault. The Burgers vectors of all these dislocations have been determined from the contrast analysis of the images and HREM observations.

Dislocation microstructures in Cu-Al-Ni shape memory alloys and their influence on martensitic transformation

It is well known that dislocations provide a very preferential nucleation points for thermoelastic martensitic transformation in shape memory alloys. Nevertheless, in ordered Cu-Al-Ni shape memory alloys, there is a coexistence of several kinds of dislocations, and their relative contribution during the martensitic transformation has not been clearly established. In this work we have studied by transmission electron microscopy the different dislocation families, in Cu-Al-Ni shape memory alloys, developed by deformation at several temperatures and after different thermomechanical treatments. The Low Angle Convergent Beam Electron Diffraction (LACBED) technique has been used because it becomes very convenient for highly anisotropic materials. We have also analysed the influence of such dislocation microstructures on the martensitic transformation.

Dislocation analysis for heat-exchanger method grown sapphire with white beam synchrotron X-ray topography

Dislocations in high quality Heat-Exchanger Method (HEM) produced sapphire were analyzed with the white beam large area transmission synchrotron X-ray topography technique. After analysis the dislocations for different Laue spots, i.e. different diffraction vectors, in one recorded film, three kinds of dislocations, i.e. screw, edge and mixed dislocations were identified in the studied HEM sapphire, but most are mixed type, whose Burgers vectors belong to the two groups of 〈2 1 ̄ 1 ̄ 0〉 and 〈1 0 1 ̄ 0〉 .

純アルミニウム双結晶における集積転位の相互作用とひずみ誘起粒界移動との関係

In order to clarify the effect of piled-up dislocations on the strain induced boundary migration (SIBM), deformation and recrystallization experiments were performed using an aluminum bicrystal specimen with twin boundary at initial orientation. During the deformation to 20% strain, inhomogeneous deformation took place near the grain boundary (GB). Two kinds of dislocations, edge and screw ones, were piled up against the GB in one component crystal. In the other crystal, edge dislocations were piled up against it. After the annealing, the SIBM was recognized along the original GB. The interaction of the piled-up dislocations was considered to occur at the GB, and it would influence the recrystallization behavior. Since the screw dislocations in one crystal were transmitted during the deformation to the other crystal through the GB because of the special orientation and geometric conditions, they could not be retained stably near or at the GB. In contrast, the edge dislocations introduced into the GB in both crystals were accumulated each other near or at the GB, thereby the component of tilt boundary took part in the original twin boundary. Therefore, it was understood that the SIBM resulted from the annihilation and rearrangement of these dislocations.

Modeling Growth Directional Features of Silicon Nanowires Obtained Using SiO

AbstractSilicon nanowires (SiNW) grown using Si monoxide source materials are mainly oriented in the <112> direction, and some in the <110> direction. These directional features may be understood by postulating that growth of the SiNW is governed by lateral advancement of {111} plane layers that are stepped, and the role of particular kinds of dislocations providing perpetuate steps.

Dislocation assessment of CdZnTe by chemical etching on both {1 1 1}B and {2 1 1}B faces

Etch pits on both {1 1 1}B and {2 1 1}B faces of ZnCdTe have been studied by etching. The Everson method has been confirmed to be a better method to show dislocations on the B face of CdZnTe and shows the same etch pit density (EPD) as that of the Nakagawa method. The further study revealed that there are two kinds of etch pits with different shapes on both {1 1 1} and {2 1 1} surfaces of CdZnTe samples etched using an Everson solution. They correspond to two different kinds of dislocations. It was also found that the EPD revealed by the E1-Ag etchant is one order of magnitude lower than that of the EPDs found using the Everson etchant, which implies that there are at least three kinds of dislocations in CdZnTe materials. The shapes of etch pits and EPD distributions were also studied in this paper.

Influence of plastic deformation on the velocity and ultrasonic attenuation of copper single crystals

High-purity copper single crystal samples were plastically deformed between 0.02% and 1% in the 111 direction. The absolute ultrasonic velocity and attenuation related to the dislocations in copper single crystal were measured as a function of the plastic deformation. The amplitude-independent Swing Model for dislocation resonance was considered to obtain information about the evolution of the dislocation density ( Λ) with the degree of plastic deformation ( ε%). The experimental data were interpreted as resulting from the contribution of two kinds of dislocations that lie in a cell structure. The results show a linear increase with the deformation of the density of dislocations ( Λ I) that lies in the cell walls [ Λ I (cm −2)≈1.5×10 9 ε%]. The dislocation density inside the cell ( Λ II) is about two orders of magnitude lower than Λ I.

TEM observations of dislocations in aluminium nitride after high temperature deformation

AlN ceramics were deformed up to 10% strain in compression at elevated temperatures (1820–1920 K) under constant stress in the range 150–250 MPa or at a constant fixed strain rate of 5×10−6 s−1. Several kinds of dislocations were identified by TEM in deformed crystals. Most of them have a→ type Burgers vectors and were seen to glide in the basal plane or in prismatic planes. They looked usually undissociated but large dissociations were observed after deformation tests of long durations. In such cases, a→ dislocations could be dissociated either by pure glide in two Shockley partials or by combined glide plus climb in two Frank–Shockley partials. In any case, the enclosed stacking fault was in the basal plane. c→+a→ dislocations were also observed but seldom. Different kinds of faulted loops are reported, delineated by Shockley, Frank or Frank–Shockley partials.Indications are given that oxygen segregation should play a role in the dissociation of dislocations.

Plastic deformation of silicon nitride single crystals

The plastic deformation behavior of silicon nitride single crystals was tested by two different methods: high temperature compression and room temperature hardness anisotropy. Macroscopic plastic deformation was observed above 1820 °C at a strain rate of 2 × 10 −5 s −1. In the deformed crystals two kinds of dislocations were found. One belonged to the slip system of 〈 11 2 ¯ 0 〉 { 1 1 ¯ 01 } . The other had a pseudo helical morphology with a Burgers vector of [0001]. Knoop hardness testing revealed that silicon nitride had isotropic character in terms of hardness. This facts supports the idea that 〈 11 2 ¯ 0 〉 { 1 1 ¯ 01 } is also the primary slip system in silicon nitride at room temperature.

Grain boundary dislocations in a Σ13 grain boundary in silicon. I. Analysis of the possible grain boundary structures and dislocations

Abstract The purpose of this paper is to describe the different grain boundary structures and kinds of dislocations which can arise in the {510} Σ13 grain boundary in diamond cubic materials. Firstly, the different possible grain boundary structures are derived within the framework of group theory, and then general expressions for the Burgers vectors of the grain boundary dislocations which separate these structures are obtained. These grain boundary dislocations are of three kinds: (1) perfect grain boundary dislocations (also called DSC dislocations), which do not change the grain boundary structure, (2) imperfect grain boundary dislocations, which relate different, but equivalent, grain boundary structures, and finally (3) partial dislocations, which separate two non-equivalent grain boundary structures. Transmission electron microscopy is then used to show that imperfect dislocations are indeed present in a Σ13 (22·6°/[001]½) grain boundary in Si, and have Burgers vectors consistent with ¼[001]½.