scholarly journals Dissociation Behavior of Dislocations in Ice

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 386
Author(s):  
Takeo Hondoh
Keyword(s):  
Basal Plane ◽  
Dislocation Line ◽  
Stacking Faults ◽  
Physical Models ◽  
Time Constants ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Perfect Dislocation ◽  
Low Energies ◽  
Dissociated State

Dislocations in ice behave very differently from those in other materials due to the very low energies of stacking faults in the ice basal plane. As a result, the dislocations dissociate on the basal plane, from a perfect dislocation into two partial dislocations with equilibrium width we ranging from 20 to 500 nm, but what is the timescale to reach this dissociated state? Using physical models, we estimate this timescale by calculating two time-constants: the dissociation-completing time td and the dissociation-beginning time tb. These time constants are calculated for two Burgers vectors as a function of temperature. For perfect dislocations with Burgers vector <c + a>, td is more than one month even at the melting temperature TM, and it exceeds 103 years below −50 ℃, meaning that the dissociation cannot be completed during deformation over laboratory timescales. However, in this case the beginning time tb is less than one second at TM, and it is within several tens of minutes above −50 ℃. These dislocations can glide on non-basal planes until they turn to the dissociated state during deformation, finally resulting in sessile extended dislocations of various widths approaching to the equilibrium value we. In contrast, for perfect dislocations with Burgers vector <a>, td is less than one second above −50 ℃, resulting in glissile extended dislocations with the equilibrium width we on the basal plane. This width is sensitive to the shear stress τ exerted normal to the dislocation line, leading to extension of the intervening stacking fault across the entire crystal grain under commonly accessible stresses. Also, due to the widely dissociated state, dislocations <a> cannot cross-slip to non-basal planes. Such behavior of extended dislocations in ice are notable when compared to those of other materials.

Threading Dislocation Density Reduction in GaN/Sapphire Heterostructures.

1999 ◽  
Vol 595 ◽  
Author(s):  
A. Kvit ◽  
A. K. Sharma ◽  
J. Narayan
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
High Density ◽  
Thin Layers ◽  
Interfacial Region ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Plan View ◽  
Partial Dislocations

AbstractLarge lattice mismatch between GaN and α-Al2O3 (15%) leads to the possibility of high threading dislocation densities in the nitride layers grown on sapphire. This investigation focused on defect reduction in GaN epitaxial thin layer was investigated as a function of processing variables. The microstructure changes from threading dislocations normal to the basal plane to stacking faults in the basal plane. The plan-view TEM and the corresponding selected-area diffraction patterns show that the film is single crystal and is aligned with a fixed epitaxial orientation to the substrate. The epitaxial relationship was found to be (0001)GaN∥(0001)Sap and [01-10]GaN∥[-12-10]Sap. This is equivalent to a 30° rotation in the basal (0001) plane. The film is found to contain a high density of stacking faults with average spacing 15 nm terminated by partial dislocations. The density of partial dislocations was estimated from plan-view TEM image to be 7×109 cm−2. The cross-section image of GaN film shows the density of stacking faults is highest in the vicinity of the interface and decreases markedly near the top of the layer. Inverted domain boundaries, which are almost perpendicular to the film surface, are also visible. The concentration of threading dislocation is relatively low (∼;2×108 cm−2), compared to misfit dislocations. The average distance between misfit dislocations was found to be 22 Å. Contrast modulations due to the strain near misfit dislocations are seen in high-resolution cross-sectional TCM micrograph of GaN/α-Al2O3 interface. This interface is sharp and does not contain any transitional layer. The interfacial region has a high density of Shockley and Frank partial dislocations. Mechanism of accommodation of tensile, sequence and tilt disorder through partial dislocation generation is discussed. In order to achieve low concentration of threading dislocations we need to establish favorable conditions for some stacking disorder in thin layers above the film-substrate interface region.

Mechanisms of Stacking Fault Growth in SiC PiN Diodes

2004 ◽  
Vol 815 ◽  
Author(s):  
R. E. Stahlbush ◽  
M. E. Twigg ◽  
J. J. Sumakeris ◽  
K. G. Irvine ◽  
P. A. Losee
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Drift Region ◽  
Pin Diodes ◽  
Current Time ◽  
Partial Dislocations ◽  
Initial Evolution ◽  
A Chain ◽  
Fault Growth

AbstractThe early development of stacking faults in SiC PiN diodes fabricated on 8° off c-axis 4H wafers has been studied. The 150μm drift region and p-n junction were epitaxially grown. The initial evolution of the stacking faults was examined by low injection electroluminescence using current-time product steps as low as 0.05 coul/cm2. The properties of the dislocations present before electrical stressing were determined based on previously observed differences of Si-core and C-core partial dislocations and the patterns of stacking fault expansion. The initial stacking fault expansion often forms a chain of equilateral triangles and at higher currents and/or longer times these triangles coalesce. All of the faulting examined in this paper originated between 10 and 40 μm below the SiC surface. The expansion rate of the bounding partial dislocations is very sensitive to the partials' line directions, their core types and the density of kinks. From these patterns it is concluded that the stacking faults originate from edge-like basal plane dislocations that have Burgers vectors either parallel or anti-parallel to the off-cut direction. Evidence for dislocation conversions between basal-plane and threading throughout the epitaxial drift region is also presented.

Cross Section and Plan View STEM Analysis on Identical Conversion Point of Basal Plane Dislocation to Threading Edge Dislocation of 4H-SiC

2016 ◽  
Vol 858 ◽  
pp. 397-400
Author(s):  
Takahiro Sato ◽  
Yoshihisa Orai ◽  
Toshiyuki Isshiki ◽  
Munetoshi Fukui ◽  
Kuniyasu Nakamura
Keyword(s):  
Cross Section ◽  
Edge Dislocation ◽  
Basal Plane ◽  
Dislocation Line ◽  
Plan View ◽  
Conversion Point ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Basal Plane Dislocation

Cross section and plan view dislocation analysis at the conversion point of a basal plane dislocation (BPD) into a threading edge dislocation (TED) in a silicon carbide epitaxial wafer was developed using a newly modified multi directional scanning transmission electron microscopy (STEM) technique. Cross section STEM observation in the [-1100] direction, found a conversion point located 5.5 μm from the surface, where two dislocation lines in the basal plane convert into one dislocation line nearly along the hexagonal c axis was observed. Using plan view STEM observation along the [000-1] direction, it is confirmed that the dislocation lines are two partial dislocations of a BPD and one TED by g·b invisibility analysis. This new technique is a powerful tool to evaluate the fundamental dislocation characteristics of power electronics devices.

The Structure of Dislocations in Low-Angle Grain Boundaries in the Diamond Cubic Lattice

1981 ◽  
Vol 5 ◽  
Author(s):  
C.B. Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Faults ◽  
Burgers Vector ◽  
Cubic Lattice ◽  
Partial Dislocations ◽  
Tilt Boundaries ◽  
P Type ◽  
Twist Boundaries

ABSTRACTDislocations in low-angle tilt boundaries exhibit a wide variety of Burgers vector including a/2<112> a<001> and a<111>. The dislocations are usually dissociated: Shohkley, stair-rod and Frank partial dislocations may each be formed together with associated intrinsic and extrinsic stackingfaults. Dislocations in low-angle {111} twist boundaries are usually assumed to dissociated by a glide mechanism to give two types of extended nodes, known as P–type and K–type, which contain intrinsic and extrinsic stacking-faults respectively. It is shown that dissociation by climb actually occurs for both types of grain boundary.

Polarized Photoluminescence from Partial Dislocations in 4H-SiC

2014 ◽  
Vol 778-780 ◽  
pp. 319-323
Author(s):  
Rii Hirano ◽  
Michio Tajima ◽  
Hidekazu Tsuchida ◽  
Kohei M. Itoh ◽  
Koji Maeda
Keyword(s):  
Room Temperature ◽  
Stacking Faults ◽  
Wave Functions ◽  
High Power Laser ◽  
Power Laser ◽  
Burgers Vector ◽  
Room Temperature Photoluminescence ◽  
Partial Dislocations ◽  
Peak Energy ◽  
Polarization Characteristics

Polarization characteristics of luminescence from partial dislocations (PDs) in 4H-SiC have been investigated by room-temperature photoluminescence (PL) imaging. After expansion of Shockley stacking faults by high-power laser irradiation, PL from PDs tilted by 6° from their Burgers vector (6°-PDs) was observed with almost the same PL peak energy as that of 30°-Si (g) PDs. The PL from the 30°-Si (g) and 6°-PDs which were mobile under illumination were both found to be polarized perpendicular to their dislocation lines. In contrast, the PL from immobile 30°-C(g) PDs was not polarized. The present results suggest that the carriers bound to the 30°-Si (g) and 6°-PDs have anisotropic wave functions and those bound to 30°-C(g)PDs have isotropic wave functions.

Overlapping Shockley/Frank Faults in 4H-SiC PiN Diodes

2006 ◽  
Vol 527-529 ◽  
pp. 383-386 ◽  
Author(s):  
Mark E. Twigg ◽  
Robert E. Stahlbush ◽  
Peter A. Losee ◽  
Can Hua Li ◽  
I. Bhat ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Light Emission ◽  
Stacking Faults ◽  
Dark Field ◽  
Pin Diodes ◽  
Plan View ◽  
Planar Defects ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Transmission Electron

Using light emission imaging (LEI), we have determined that not all planar defects in 4H-SiC PiN diodes expand in response to bias. Accordingly, plan-view transmission electron microscopy (TEM) observations of these diodes indicate that these static planar defects are different in structure from the mobile stacking faults (SFs) that have been previously observed in 4H-SiC PiN diodes. Bright and dark field TEM observations reveal that such planar defects are bounded by partial dislocations, and that the SFs associated with these partials display both Frank and Shockley character. That is, the Burgers vector of such partial dislocations is 1/12<4-403>. For sessile Frank partial dislocations, glide is severely constrained by the need to inject either atoms or vacancies into the expanding faulted layer. Furthermore, these overlapping SFs are seen to be fundamentally different from other planar defects found in 4H-SiC.

CBED analysis of extended defects in melt-grown GaSe single crystals

1990 ◽  
Vol 48 (4) ◽  
pp. 494-495
Author(s):  
C. De Blasi ◽  
D. Manno
Keyword(s):  
Single Crystals ◽  
Displacement Vector ◽  
Stacking Faults ◽  
Convergent Beam Electron Diffraction ◽  
Extended Defects ◽  
Burgers Vector ◽  
First Order ◽  
Partial Dislocations ◽  
Kinematical Condition ◽  
Convergent Beam

The study of dislocations and stacking faults in melt grown GaSe single crystals has been carried out by the Convergent Beam Electron Diffraction (CBED) technique.The presence of stacking faults induces distortions in the Kikuchi lines observed in the CBED transmitted disk. According to the kinematical condition of the stacking fault visibility, such lines show modifications when g·R is not integer, The displacement vector R has been determined by the analysis of the visibility and invisibility conditions in the transmitted disk, recorded according to the Tanaka method, The Burgers vector b of dislocations has been determined by the analysis of the modifications induced both in Kikuchi lines and in the First Order Laue Zone (FOLZ) reflections, observed in low camera length CBED patterns. Splitting and unsplitting of the reflections correspond to the visibility and invisibility of the dislocations in the kinematical approximation of diffraction contrast, The condition g·b = 0 is not strictly a sufficient condition for the vanishing of the modifications induced by the dislocation, neverthless it is generally very useful as a criterion for determining the direction of b, Moreover, some reflections g give g·b = ⅓ in the case of partial dislocations. This condition does not produce enough contrast to be detected, so that it is one more for the defect invisibility. The Thompson construction has been used in order to calculate the amplitude of b and to discriminate perfect or partial dislocations.

The role of structural imperfections in the photodimerization of 9-cyanoanthracene

1971 ◽  
Vol 324 (1559) ◽  
pp. 459-468 ◽  
Keyword(s):  
Fluorescence Microscopy ◽  
Excitation Energy ◽  
Slip Plane ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Structural Imperfections ◽  
Active Slip

Crystalline 9-cyanoanthracene undergoes photodimerization to give the trans dimer which is unexpected on the basis of the topochemical preformation theory. The possibility that the reaction occurs at defects is investigated; and the nature of the structural imperfections are described, as are also the types of product nuclei and their modes of growth. Interference-contrast and fluorescence microscopy have been employed for the examination of cleaved and partially dimerized faces of the monomer. It is shown that there is an active slip plane (221), and consideration of feasible dislocation reactions, particularly those involving unit strength dislocations which have a component of the Burgers vector in [100], reveals that, within stacking-fault regions (bounded by partial dislocations), the monomer molecules are in trans registry. It is suggested that molecules in such stacking faults act as traps for the excitation energy, and that reaction occurs at these sites.

Direct Observation of Stacking Fault Nucleation from Deflected Threading Dislocations with Burgers Vector c+a in PVT Grown 4H-SiC

2014 ◽  
Vol 1693 ◽  
Author(s):  
Fangzhen Wu ◽  
Huanhuan Wang ◽  
Balaji Raghothamachar ◽  
Michael Dudley ◽  
Stephan G. Mueller ◽  
...  
Keyword(s):  
Direct Observation ◽  
Basal Plane ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Formation Mechanisms ◽  
Threading Dislocations ◽  
Burgers Vector ◽  
X Ray ◽  
Transmission Geometry ◽  
Made In

ABSTRACTIn our previous studies [1-3], four kinds of stacking faults in 4H-SiC bulk crystal have been distinguished based on their contrast behavior differences in synchrotron white beam x-ray topography images. These faults are Shockley faults, Frank faults, Shockley plus c/2 Frank faults, and Shockley plus c/4 Frank faults. Our proposed formation mechanisms for these stacking faults involve the overgrowth of the surface outcrop associated with threading screw dislocations (TSDs) or threading mixed dislocations (TMDs) with Burgers vector of c+a by macrosteps and the consequent deflection of TSDs or TMDs onto the basal plane. Previous synchrotron x-ray topography observations were made in offcut basal wafers using transmission geometry. In this paper, further evidence is reported to confirm the proposed stacking fault formation mechanism. Observations are made in axially cut slices with surface plane {11-20}. Several kinds of stacking faults are recognized and their contrast behavior agrees with the four kinds previously reported. Direct observation is obtained of a Shockley plus c/4 Frank stacking fault nucleating from a TMD deflected onto the basal plane. The contrast from stacking faults on the basal plane in the axial slices is enhanced by recording images after rotating the crystal about the active -1010 reflection vector enabling a broader projection of the basal plane.

Deflection of Threading Dislocations with Burgers Vector c/c+a Observed in 4H-SiC PVT–Grown Substrates with Associated Stacking Faults

2012 ◽  
Vol 717-720 ◽  
pp. 347-350 ◽  
Author(s):  
Sha Yan Byrapa ◽  
Fang Zhen Wu ◽  
Huan Huan Wang ◽  
Balaji Raghothamachar ◽  
Gloria Choi ◽  
...  
Keyword(s):  
Detailed Analysis ◽  
Basal Plane ◽  
Stacking Faults ◽  
Image Contrast ◽  
Threading Dislocations ◽  
Burgers Vector ◽  
Calculated Phase ◽  
X Ray ◽  
White Beam ◽  
Contrast Studies

A review is presented of Synchrotron White Beam X-ray Topography (SWBXT) studies of stacking faults observed in PVT-Grown 4H-SiC crystals. A detailed analysis of various interesting phenomena were performed and one such observation is the deflection of threading dislocations with Burgers vector c/c+a onto the basal plane and associated stacking faults. Based on the model involving macrostep overgrowth of surface outcrops of threading dislocations, SWBXT image contrast studies of these stacking faults on different reflections and comparison with calculated phase shits for postulated fault vectors, has revealed faults to be of basically four types: (a) Frank faults; (b) Shockley faults; (c) Combined Shockley + Frank faults with fault vector s+c/2; (d) Combined Shockley + Frank faults with fault vector s+c/4.

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