Dislocation Sites Research Articles

Dislocation-assisted complex scattering mobility of electrons in plastically deformed n-GaAs single crystals

DC conductivity and Hall effect measurements are made in undeformed and plastically deformed (by indentation) n-type GaAs samples between 77 and 300 K. The studies show that the dislocation-assisted vacancy complexes of activation energy 0.015-0.010 eV are present in deformed samples. The electron mobility of these samples is explained by considering different scattering processes. In plastically deformed samples an additional scattering mobility due to dislocation-assisted vacancy complexes is suggested to explain the experimental mobilities. The centres responsible for this scattering are associated with native vacancy complexes segregated at the dislocation sites. The fresh dislocation motion, mainly α-dislocations (with higher mobility than β-dislocations) help the creation and movement of acceptor vacancies and their segregation as complexes at the dislocation sites. The complex scattering mobility of electrons has been found to vary linearly with temperature in all the deformed samples. These complexes are also found to be temperature-insensitive throughout the extrinsic region of the sample.

Effect of Cold Deformation and Hydrogen Charging on TTF and Hardness of 0.1 C Steel

Introduction Plastic deformation of steel causes crystalline imperfections such as increased dislocation density, vacancies, cracks and microvoids which, in turn, influence dissolution and transport of hydrogen in traps. The increased dislocation density and dislocation pile‐ups against cementile lamella or non‐metallic inclusions lead to microcrack formation. The dislocation pile‐ups are mobile under stress. Transport of hydrogen by dislocation under stress can be expected but the temperature should be neither so high as to force the hydrogen to leave the dislocation sites nor so low that the hydrogen cannot diffuse into the dislocation sites.

Cu単結晶 (111) 面の丸川液による溶解に及ぼす温度の影響

The (111) surface of copper crystal was etched for 10 s at temperatures 270 to 290 K with Marukawa’s etchant containing FeCl3·6H2O 0.88 kmol·m−3, HCl 4.4 kmol·m−3 and HBr 0.12 kmol·m−3. The dissolved thickness of matrix surface S was determined by a two-beam interferometric measurement of the step height produced at the boundary between neighboring areas exposed and unexposed to the etchant. The width h and depth d of etch pits of triangular pyramidal shape developed at screw dislocation sites were measured by replica electron microscopy. The lateral dissolved length and the normal dissolved depth at the dislocation sites, H and D, were determined from S, h and d, respectively.As the etching temperature was raised, all of H, D, D/H and S increased monotonically. It was shown that these results could be explained qualitatively on the basis of the spiral theory of crystal dissolution at screw dislocation and the two-dimensional nucleation theory at dislocation-free surface, respectively.

Model for Suppression of Dislocation Etch Pits in Vacuum-Swept Quartz Crystals

It is well known that vacuum-swept quartz crystals do not show dislocation etch pits upon etching, whereas X-ray topographic studies show that the dislocation network remains the same. A model is presented to show that there is no preferential dissolution by the etchant at the dislocation sites in vacuum-swept crystals.

Cu単結晶 (111) 面の溶解に及ぼす丸川液中の溶解抑制剤臭化水素酸濃度の影響

The dissolution at screw dislocation sites and dislocation-free sites of the Cu (111) surface was studied as a function of concentration of HBr in Marukawa’s etchant (FeCl3·6H2O-HCl-HBr). Etching was carried out for 10 s at 280 K, and the dissolved quantities along lateral and longitudinal directions at dislocation, H and D, and the dissolved thickness of the matrix surface, S, were determined from measurement of size of dislocation etch pits and the step height at the boundary between the masked surface and the etched surface, respectively. An increase of the concentration of HBr in the etchant caused a decrease in H and an increase in D, but it produced no change in S. The role of inhibitor HBr was discussed on the basis of the spiral theory of crystal dissolution at screw dislocation and the two-dimensional nucleation theory at dislocation-free surface.

Studies on dislocation etching kinetics of flux-grown YFeO 3 crystals

Results of etching (110) and (001) planes of YFeO 3 crystals are presented and discussed in detail. It is shown that boiling H 3PO 4 or H 3PO 4+HNO 3 in the ratio of 1:1 is the dislocation etchant of YFeO 3 crystals. It is established that the latter etchant is best suited for both (110) and (001) planes insofar as the definition of pit and control over etching are concerned. The kinetics of etching are investigated by making a quantitative study of the etch rate at different temperatures and at different concentrations of H 3PO 4. Variations in areal extension and depth of pits with time in H 3PO 4 or H 3PO 4 mixed with HNO 3 are investigated. It is shown that the areal and vertical etch rates increase with increase in temperature on both (110) and (001) planes. Addition of HNO 3 to H 3PO 4 brings down the minimum temperature required for etching (110) and (001) planes. The velocities of dissolution parallel and perpendicular to the surface are measured. The activation energy responsible for the dislocation sites for dissolution parallel and perpendicular to (110) and (001) planes are estimated. The Arrhenius factors for areal ( A' A ) and vertical ( A D ) dissolution are A' A =1.44×10 9 and 3.99×10 7 μm/s, and A D =8.12×10 3 and 1.31×10 4 μm/s for (110) and (001) planes, respectively.

Computer Simulation of the Interaction Between An Extended Dislocation and Radiation Defects in the fcc Lattice

The interaction between an extended dislocation and a radiation-induced defect, especially a self-intersistial atom (SIA), has been investigated in the model fcc lattice by computer simulation technique. An SIA was absorbed into the core of one of the two partial dislocations of the extended screw dislocation as a crowdion which extends along the dislocation line. Under the applied shear stress this crowdion acted as a pinning point, resulting in irradiation hardening. On the other hand, an SIA was absorbed at the jog site of the extended edge dislocation (at one of the two jog sites on two partial dislocations) and after some relaxation the total jog was shifted to one atomic distance through the spreading out of the strain due to an SIA from one partial side to the other side

On the formation of etch grooves at impurity striations and growth sector boundaries in crystals grown from solutions

A theory of formation of etch grooves at planar defects like impurity striations and growth sector boundaries by chemical etching is proposed. The theory is based on the concept of the thermodynamic theories of etch-pit formation at dislocation sites, in combination with the concept of the existence of a pseudomorphous deformed layer in the region of impurity microsegregation, the latter concept being taken from epitaxy. After estimates of thickness of the deformed layer, equations are derived for the free energy change involved in the formation of etch grooves at planar defects, and for the slope of the etch grooves. Among important predictions of the theory, the following may be enumerated: (1) Etching media in which a crystal is more soluble (i.e. fast etchants), yield contrasting grooves. (2) The capability of revelation of planar defects on different faces of a crystal by an etchant decreases with increasing morphological importance of the faces. (3) All fast dislocation etchants are also good etchants for revealing etch grooves at planar defects. The theoretical predictions are then compared with the experimental results on the revelation of etch grooves on different faces of KDP and other crystals grown from aqueous solutions. It is found that the theory satisfactorily explains the experimental results.

The growth of large scales at defect sites in the plane mixing layer

The evolution of vortex structure in the vicinity of a pattern defect or dislocation, generated experimentally by forcing a high Reynolds number mixing layer, is studied using a new two-dimensional wavelet transform called Arc. This transform localizes spectral information in physical space – as all wavelets do – but is not direction-specific in wavenumber space. Various types of forcing, including forcing at the fundamental and subharmonic wavenumbers, produce a range of mixing-layer responses. The most significant finding is that a dislocation site acts as a nucleus and initiates a rapid, localized evolution to larger scales. The area of the localized ‘patch’ grows approximately as the square of downstream distance. Defect-initiated patches bear generic similarities to the disturbed regions in cylinder wakes – commented upon recently by many researchers – and in particular to the Λ-structures described by Williamson (1992).

Cu単結晶(111)面の280 Kにおける丸川液腐食によるらせん転位位置の溶解速度

The dissolution process of (111) faces of Cu crystals in Marukawa’s solution (FeCl3·6H2O 0.88 kmol·m−3, HCl 4.4 kmol·m−3, HBr 0.12 kmol·m−3) was studied. The etching was carried out at 280 K for 10-50 s, and the three-dimensional size of etch pits revealed at screw dislocations and the dissolved thickness of the matrix surface were measured by replica electron microscopy and two-beam interferometry, respectively.After an initial lapse of 10 s, the width and depth of dislocation etch pits increased linearly with the etching time, while the side slope of etch pits decreased slowly and approached a constant value of 0.1. The dissolved thickness of the matrix surface increased also linearly with the etching time. From the growth rate of etch pits and the removal rate of the matrix surface, the vertical dissolution rate along the dislocation line, vd, and the lateral one, vh, were determined. Using these values, it has been estimated from the spiral theory of crystal dissolution at a screw dislocation site that the spacing of a spiral step is ∼2.1×10−3 μm and that the radius of curvature at a spiral center, which is equal to the size of critical nucleus for two-dimensional nucleation on a stress-free surface, is 1.1×10−4-5.3×10−4 μm. From the nucleation theory of matrix surface dissolution, the rate of two-dimensional nucleation on the dislocation-free surface has been deduced to be 4.3×105 μm−2·s−1.

Etching studies on (1 0 0) faces of gel-grown ammonium dihydrogen orthophosphate crystals

Chemical etching employing specific etchants with varying etch times (20–60 s) has been successfully applied for the first time to reveal dislocation sites on the polished (1 0 0) faces of ammonium dihydrogen orthophosphate single crystals grown at ambient temperature, using a modified gel technique of double diffusion in a U-shaped beaker assembly. The selective behaviour of the etchant for straight and inclined dislocations has been demonstrated. Growth striations due to temperature fluctuations, low-angle tilt boundary and etch channels corresponding to stacking faults were clearly observed. Surface structures of the etched faces were photographed by optical and scanning electron microscopes and are discussed.

Effect of Fluorine on the Dopant Diffusion of Through-Oxtoe Implanted Boron in Si - a Correlation with Microstructural Defects

ABSTRACTIn case of boron through-oxide implant, it has been shown that the knocked-in oxygen atoms segregate at initially nucleated dislocation sites during the incubation and no significant junction movement is detected. The trapping of oxygen proceeds up to a certain time at which oxygen-precipitation occurs and this leads to an ejection of excess Si interstitials and further enhancing boron diffusion. However, with fluorine addition we believe that fluorine incorporation in SiO2 and/or SiO2/Si interface not only releases the strain gradient but also suppresses the silicon interstitials ejection and by this means suppresses the oxidation-enhanced boron diffusion. Correlated results of TEM microdefect structures and spreading resistance profiles are used to further support our postulation.

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

AbstractAn 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.

Characterization of CdTe crystals by chemical etching and cathodoluminescence measurements

A double etch process has been developed, based on the well-known Inoue etch solution, in order to achieve greater control over the generation of etch pits on CdTe crystals. A comparison of the resulting etch patterns with those generated by applying another well-known (Nakagawa) etchant suggests an attacking of extended crystal defects by the former and a more sensitive etching of dislocation sites by the latter etchant. Since such extended crystal defects are correlated with precipitates in the crystals, the etching procedure allows a major excess concentrations of Cd or Te to be spatially resolved. The character of these precipitates was measured by cathodoluminescence and was found to be spotty for CdTe crystals grown under high Cd excess and more threaded when grown under high Te excess in the melt.

Detection of lattice defects in ferroelectric lead hydrogen phosphate crystals by chemical etching

Single crystals of the LHP up to 7×4×3 mm 3 in size are grown by employing the gel technique. The crystals have found to possess only one perfect cleavage, viz. (110). The nitric acid solution and ammonium perchloric acid at various concentrations are able to reveal satisfactorily the dislocation content of the LHP crystal. Well defined etch pits are traceable on etching of isolated (010) and (110) cleavages of matched pairs revealing the sites of dislocations. Almost all dislocations studied are linear, inclined and parallel. The average density of dislocations is 3×10 2 cm −2 . Low angle boundaries are perferentially attacked during etching

Titanium wire internal fixation for stabilization of injury of the cervical spine: clinical results and postoperative magnetic resonance imaging of the spinal cord.

Nine patients with dislocation of the cervical spinal with posterior ligamentous damage were treated with posterior internal fixation using a twisted pair of 22-gauge titanium wires and iliac crest bone fusion. Fixation using the titanium wire was compared with fixation using stainless steel wire for differences in surgical insertion, long term stability of bony fusion, and postoperative magnetic resonance imaging (MRI) artifacts near the implanted wire. MRI of the cervical spine is valuable for diagnosing the acute and chronic consequences of traumatic cervical spinal injury by providing anatomic evaluation of both the spinal cord and the supporting bony/ligamentous structures in the neck. Because MRI is an accurate and sensitive noninvasive test, it is especially useful for the long-term serial assessment of the region near the cervical dislocation site to detect the sequelae of spinal cord injury, including syrinx, arachnoid cyst, cord tethering, and persistent mechanical impingement on the spinal cord or spinal roots. Previous attempts at our institution to obtain useful MRI scans of the cervical region adjacent to stainless steel wires after posterior wire fixation have failed due to marked imaging artifacts from the ferromagnetic properties of these wires. Our substitution of biocompatible titanium wire (Titanium 6 A1-4V ELI alloy, Specialty Steel and Forge, Leonia, New Jersey) for stainless steel wire produced identical immediate stabilization and ultimate bony fusion of the fracture and yielded minimal MRI artifacts overlying the immediately adjacent spinal cord and neural canal; however, the installation was technically more difficult, because of the titanium wire's greater stiffness.(ABSTRACT TRUNCATED AT 250 WORDS)

Titanium Wire Internal Fixation for Stabilization of Injury of the Cervical Spine: Clinical Results and Postoperative Magnetic Resonance Imaging of the Spinal Cord

Abstract Nine patients with dislocation of the cervical spinal with posterior ligamentous damage were treated with posterior internal fixation using a twisted pair of 22-gauge titanium wires and iliac crest bone fusion. Fixation using the titanium wire was compared with fixation using stainless steel wire for differences in surgical insertion, long term stability of bony fusion, and postoperative magnetic resonance imaging (MRI) artifacts near the implanted wire. MRI of the cervical spine is valuable for diagnosing the acute and chronic consequences of traumatic cervical spinal injury by providing anatomic evaluation of both the spinal cord and the supporting bony/ligamentous structures in the neck. Because MRI is an accurate and sensitive noninvasive test, it is especially useful for the long-term serial assessment of the region near the cervical dislocation site to detect the sequelae of spinal cord injury, including syrinx, arachnoid cyst, cord tethering, and persistent mechanical impingement on the spinal cord or spinal roots. Previous attempts at our institution to obtain useful MRI scans of the cervical region adjacent to stainless steel wires after posterior wire fixation have failed due to marked imaging artifacts arising from the ferromagnetic properties of these wires. Our substitution of biocompatible titanium wire (Titanium 6 A1-4V ELI alloy, Specialty Steel and Forge, Leonia, New Jersey) for stainless steel wire produced identical immediate stabilization and ultimate bony fusion of the fracture and yielded minimal MRI artifacts overlying the immediately adjacent spinal cord and neural canal; however, the installation was technically more difficult, because of the titanium wire's greater stiffness. We believe that the implantation of a permancent fixation device in these patients should be made of an MRI-compatible material, such as titanium wire, to allow serial imaging with MRI in their lifelong medical care.

Growth and characterisation of triammonium citrate

Single crystals of triammonium citrate are grown from aqueous solution and characterized using X-ray and etching studies. Using single crystal X-ray diffraction, the crystal is found to be orthorhombic with lattice parametersa = 6·223 Å,b = 15·048 Å andc = 11·056 Å. Surface studies on the as-grown faces reveal stratigraphic patterns. Of the several etchants tried, glacial acetic acid appears to be the best etchant for revealing dislocation sites on the as-grown faces.

Young液によるCu単結晶(111)面の溶解速度の温度依存性

The effect of etching temperature on the dissolution rates at edge dislocation sites and dislocation-free sites of the (111) surface of copper single crystals was studied. The etching was carried out at temperatures 270 to 285 K for 5 to 25 s with Young’s etchant containing (NH4)2S2O8 1 kmol·m−3, NH4OH 6 kmol·m−3 and NH4Br 0.3 kmol·m−3. From the measured data on the width and depth of dislocation etch pits and the dissolved thickness of the (111) matrix surface as a function of etching time, the linear dissolution rates parallel and normal to the surface at dislocation sites, vh and vd, and the dissolution rate normal to the surface at dislocation-free sites, vs, were calculated. As a result, it was found that the dissolution rates were in the order of vh>vd>vs at any temperature and that they increased as the etching temperature increased. These results were qualitatively discussed by the kinetic theory of two-dimensional nucleation and step motion for crystal dissolution and some kinetic quantities relating to the formation of two-dimensional nucleus and the step motion were evaluated.

Hydrogen mobility parameters and dislocation pinning rates at very low temperatures in tantalum

Pinning rates of dislocations by hydrogen and deuterium have been analysed in monocrystalline tantalum samples of ultrahigh purity. For this purpose, measurements of internal friction and elastic modulus were performed down to 2 K, using a vibrating strip system. A marked pinning stage located between 8 K and 11 K was revealed for hydrogen. The authors show that it reflects the arrival of the hydrogen atoms at dislocation sites, resulting in the pinning of the dislocation kinks. The inferred jump rate of hydrogen atoms is 3*102+or-1 s-1 at 8.3 K. The temperature dependence of diffusion was found to obey a power law, with a large exponent, 15+or-3. Deuterium migration was also detected, at around 14 K. The results obtained are compared with previous data at higher or similar temperatures and discussed in relation to the existing theories for quantum diffusion.