Статті в журналах: "Densités des dislocations"

1

Li, Yon Gan, Xiang Qian Xiu, Xue Mei Hua, Shi Ying Zhang, Shi Pu Gu, Rong Zhang, Zi Li Xie, et al. "Study of Dislocation Densities of Thick GaN Films." Advanced Materials Research 989-994 (July 2014): 387–90. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.387.

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The dislocation density of GaN thick films has been measured by high-resolution X-ray diffraction. The results show that both the edge dislocations and the screw dislocation reduce with increasing the GaN thickness. And the edge dislocations have a larger fraction of the total dislocation densities, and the densities for the edge dislocation with increasing thickness reduce less in contrast with those for the screw dislocation.

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2

Muiruri, Amos, Maina Maringa, and Willie du Preez. "Evaluation of Dislocation Densities in Various Microstructures of Additively Manufactured Ti6Al4V (Eli) by the Method of X-ray Diffraction." Materials 13, no. 23 (November 26, 2020): 5355. http://dx.doi.org/10.3390/ma13235355.

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Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities.

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3

Herring, R. A., P. N. Uppal, S. P. Svensson, and J. S. Ahearn. "TEM characterization of dislocation reduction processes in GaAs/Si." Proceedings, annual meeting, Electron Microscopy Society of America 47 (August 6, 1989): 590–91. http://dx.doi.org/10.1017/s0424820100154925.

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A high density of interfacial dislocations are needed at the GaAs/Si interface to alleviate the 4% lattice mismatch between GaAs and Si. Some remnant dislocations thread through the epilayer and follow the growth interface. Current growth methods are not able to obtain acceptable threading dislocation densities (104 – 105) for devices. Many methods can be used to reduce the number of threading dislocations which include misorienting the substrate to enhance the slip of dislocations on specific [110]{111} planes, annealing during and after growth, and adding strained layer superlattices (SLS's) to block dislocations. Conventional TEM (CTEM), performed using a JEM 100c, has been used to characterize threading dislocations in the epilayer of a GaAs/Si material where in situ thermal annealing and SLS's force dislocation reactions and thereby reduce the threading dislocation density. Using TEM we have viewed dislocations under many two-beam diffraction conditions and with the help of a stereogram have determined their Burgers vectors (b), line directions (u) and habit planes (R).

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4

Rezvanian, O., M. A. Zikry, and A. M. Rajendran. "Statistically stored, geometrically necessary and grain boundary dislocation densities: microstructural representation and modelling." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2087 (August 14, 2007): 2833–53. http://dx.doi.org/10.1098/rspa.2007.0020.

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A unified physically based microstructural representation of f.c.c. crystalline materials has been developed and implemented to investigate the microstructural behaviour of f.c.c. crystalline aggregates under inelastic deformations. The proposed framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs) and grain boundary dislocations. This interrelated dislocation density formulation is then coupled to a specialized finite element framework to study the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic crystalline deformation. The GND densities are used to understand where crystallographic, non-crystallographic and cellular microstructures form and the nature of their dislocation composition. The SSD densities are formulated to represent dislocation cell microstructures to obtain predictions related to the inhomogeneous distribution of SSDs. The effects of the lattice misorientations at the grain boundaries (GBs) have been included by accounting for the densities of the misfit dislocations at the GBs that accommodate these misorientations. By directly accounting for the misfit dislocations, the strength of the boundary regions can be more accurately represented to account for phenomena associated with the effects of the GB strength on intergranular deformation heterogeneities, stress localization and the nucleation of failure surfaces at critical regions, such as triple junctions.

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5

Trishkina, L. I., T. V. Cherkasova, A. A. Klopotov, and A. I. Potekaev. "Mechanisms of Solid-Solution Hardening of Single-Phase Cu-Al and Cu-Mn Alloys with a Mesh Dislocation Substructure." Izvestiya of Altai State University, no. 4(120) (September 10, 2021): 59–65. http://dx.doi.org/10.14258/izvasu(2021)4-09.

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The dislocation structure and dislocation accumulation during deformation of polycrystalline FCC solid solutions of Cu-Al and Cu-Mn systems are studied by transmission diffraction electron microscopy. The Al content in Cu-Al alloys varies from 0.5 to 14 at.%. The Mn content in Cu-Mn alloys varies in the range of 0.4 ÷ 25 at.%. Alloys with a grain size in the range of 20 ÷ 240 µm are studied. The alloy samples are deformed by stretching at a rate of 2×10-2c-1 to failure at 293 K. The structure of samples deformed to various degrees of deformation is studied on foils using electron microscopes at an accelerating voltage of 125 kV. For each degree of deformation, the scalar dislocation density and its components are measured: statistically stored dislocations ρS and geometrically necessary dislocations ρG and some other parameters of the defective structure. The mechanisms and their contributions due to mesh and mesh-mesh dislocation substructures (DSS) are determined using the example of substructural and solid-solution hardening in polycrystalline Cu-Al and Cu-Mn alloys. The relative role of various mechanisms in the formation of the resistance to deformation of alloys at different grain sizes is determined. The role of the packaging defect energy on the value of solid-solution hardening for different grain sizes is revealed. The average scalar dislocation density is considered and determined along with its components: statistically stored dislocations ρS and geometrically necessary dislocations ρG. The dependences of the flow stress on the square root of the densities of geometrically necessary dislocations and the densities of statistically stored dislocations are found.

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6

Botros, K. Z., and S. S. Sheinin. "A method for avoiding errors in measurements of dislocation density in specimens with a high dislocation density." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 1458–59. http://dx.doi.org/10.1017/s0424820100131929.

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The measurement of dislocation density from electron microscope images of dislocations is an important tool in the hands of the materials scientist. Weak beam images are often chosen for this purpose. In cases where the dislocation density is high, there is a strong possibility that the imaging electrons propagating through the thin foil would encounter several dislocations before emerging from the bottom surface. A question which arises is what effect this may have on image contrast and whether this affects measurements of dislocation density.The authors of this paper have addressed this question by examining the contrast obtained in the case where two dislocations overlap so that the imaging electrons encounter two dislocations before reaching the bottom surface of the specimen. The details of these calculations are presented elsewhere and will not be repeated here. For purposes of this paper, the results can be summarized by stating that, for certain diffraction conditions and dislocation separations, the contrast exhibited by the overlapping dislocation configuration is very weak with the result that the dislocations would not be observed.

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7

Lauer, Kevin, Martin Herms, Anett Grochocki, and Joachim Bollmann. "Iron Gettering at Slip Dislocations in Czochralski Silicon." Solid State Phenomena 178-179 (August 2011): 211–16. http://dx.doi.org/10.4028/www.scientific.net/ssp.178-179.211.

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The impact of slip dislocations on the interstitial iron distribution in as-grown CZ silicon wafers is investigated by calibrated MWPCD excess charge carrier lifetime measurements, DLTS measurements and measurements of the dislocation density. In regions of high dislocation density low interstitial iron content as well as low lifetime is observed. A linear correlation between dislocation density and interstitial iron content is found. We explain this linear correlation by the thesis that slip dislocations are 60° dislocations, which have adsorbed one iron atom at each dangling bond along the dislocation axis. Interstitial iron is gettered by slip dislocations but iron silicide, which forms along the dislocation axis, is a very strong recombination center for excess charge carriers as well. Hence, gettering of interstitial iron at slip dislocations does not increase the electrical quality of silicon.

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8

Dalmau, Rafael, Jeffrey Britt, Hao Yang Fang, Balaji Raghothamachar, Michael Dudley, and Raoul Schlesser. "X-Ray Topography Characterization of Large Diameter AlN Single Crystal Substrates." Materials Science Forum 1004 (July 2020): 63–68. http://dx.doi.org/10.4028/www.scientific.net/msf.1004.63.

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Large diameter aluminum nitride (AlN) substrates, up to 50 mm, were manufactured from single crystal boules grown by physical vapor transport (PVT). Synchrotron-based x-ray topography (XRT) was used to characterize the density, distribution, and type of dislocations. White beam topography images acquired in transmission geometry were used to analyze basal plane dislocations (BPDs) and low angle grain boundaries (LAGBs), while monochromatic beam, grazing incidence images were used to analyze threading dislocations. Boule diameter expansion, without the introduction of LAGBs around the periphery, was shown. A 48 mm substrate with a uniform threading dislocation density below 7.0 x 102 cm-2 and a BPD of 0 cm-2, the lowest dislocation densities reported to date for an AlN single crystal this size, was demonstrated.

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9

Estrin, Y., H. Braasch, and Y. Brechet. "A Dislocation Density Based Constitutive Model for Cyclic Deformation." Journal of Engineering Materials and Technology 118, no. 4 (October 1, 1996): 441–47. http://dx.doi.org/10.1115/1.2805940.

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A new constitutive model describing material response to cyclic loading is presented. The model includes dislocation densities as internal variables characterizing the microstructural state of the material. In the formulation of the constitutive equations, the dislocation density evolution resulting from interactions between dislocations in channel-like dislocation patterns is considered. The capabilities of the model are demonstrated for INCONEL 738 LC and Alloy 800H.

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10

Yakimov, Eugene B. "EBIC Investigations of Deformation Induced Defects in Si." Solid State Phenomena 131-133 (October 2007): 529–34. http://dx.doi.org/10.4028/www.scientific.net/ssp.131-133.529.

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Calculation of relation between the EBIC contrast and the recombination strength for dislocations and quasi-two-dimensional dislocation trails has been carried out taking into account the real values of depletion region width. Using the relations obtained the linear defect density along dislocations and sheet density in dislocation trails are estimated. The results of EBIC investigations of dislocations and dislocation trails in plastically deformed n- and p-Si are analyzed.

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11

Takaki, Setsuo, Y. Fujimura, Koichi Nakashima, and Toshihiro Tsuchiyama. "Effect of Dislocation Distribution on the Yielding of Highly Dislocated Iron." Materials Science Forum 539-543 (March 2007): 228–33. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.228.

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Yield strength of highly dislocated metals is known to be directly proportional to the square root of dislocation density (ρ), so called Bailey-Hirsch relationship. In general, the microstructure of heavily cold worked iron is characterized by cellar tangled dislocations. On the other hand, the dislocation substructure of martensite is characterized by randomly distributed dislocations although it has almost same or higher dislocation density in comparison with heavily cold worked iron. In this paper, yielding behavior of ultra low carbon martensite (Fe-18%Ni alloy) was discussed in connection with microstructural change during cold working. Originally, the elastic proportional limit and 0.2% proof stress is low in as-quenched martensite in spite of its high dislocation density. Small amount of cold rolling results in the decrease of dislocation density from 6.8x1015/m-2 to 3.4x1015/m-2 but both the elastic proportional limit and 0.2% proof stress are markedly increased by contraries. 0.2% proof stress of cold-rolled martensite could be plotted on the extended line of the Bailey-Hirsch equation obtained in cold-rolled iron. It was also confirmed that small amount of cold rolling causes a clear microstructural change from randomly distributed dislocations to cellar tangled dislocations. Martensite contains two types of dislocations; statistically stored dislocation (SS-dislocation) and geometrically necessary dislocation (GN-dislocation). In the early deformation stage, SS-dislocations easily disappear through the dislocation interaction and movement to grain boundaries or surface. This process produces a plastic strain and lowers the elastic proportional limit and 0.2% proof stress in the ultra low carbon martensite.

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12

Wang, Wen, Dan Wang, and Fu Sheng Han. "Mechanical Behavior of Twinning Induced Plasticity Steel Processed by Warm Forging and Annealing." Defect and Diffusion Forum 385 (July 2018): 21–26. http://dx.doi.org/10.4028/www.scientific.net/ddf.385.21.

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The present study shows that warmly forged and low-temperature annealed twinning induced plasticity (TWIP) steel exhibited very high dislocation density and apparent yield-point phenomenon in addition to very high yield strength. The initial density of dislocations significantly affected the evolution of dislocations during the subsequent tensile deformation. Original high dense dislocations prompted the rapid increase of dislocations, and intensified the complexity of dislocation configurations. All these effects made the twinning deformation weakened but the dislocation deformation enhanced, leading to increased strength but decreased plasticity.

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13

Vermeulen, A. C., R. Delhez, Th H. de Keijser, and E. J. Mittemeijer. "X-Ray Diffraction Analysis of Simultaneous Changes in Stress and Dislocation Densities in Thin Films." Advances in X-ray Analysis 39 (1995): 195–210. http://dx.doi.org/10.1154/s0376030800022606.

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A method has heen developed to determine the dislocation configuration in a polycrystalline specimen from the direction dependence of line broadening. The method is based on an analytical expression for the integral breadth due to microstrain from sets of parallel edge and/or screw dislocations on the specific slip systems. Analysis of the x-ray-diffraction measurements obtained from poly crystalline aluminium layers, deposited onto silicon wafers and subsequently annealed and cooled to room temperature, shows unequal densities and unequal changes of densities of dislocations with the Burgers vector parallel and with the Burgers vector inclined with respect to the surface of the layer. Stress relaxation and dislocation annihilation occur at room temperature. A model was developed to describe the dependency of the decrease of macrostress on the decrease of the dislocation density.

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14

Leonard, R. T., M. J. Paisley, S. Bubel, J. J. Sumakeris, A. R. Powell, Y. Khlebnikov, J. C. Seaman, et al. "Exploration of Bulk and Epitaxy Defects in 4H-SiC Using Large Scale Optical Characterization." Materials Science Forum 897 (May 2017): 226–29. http://dx.doi.org/10.4028/www.scientific.net/msf.897.226.

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In this work, aggregate epitaxial carrot distributions are observed at the crystal, wafer and dislocation defect levels, instead of individual extended carrot defect level. From combining large volumes of data, carrots are observed when both threading screw dislocations (TSD) and basal plane dislocations (BPD) densities are locally high as seen in full wafer maps. Dislocation density distributions in areas of carrot formation are shown, and suggest TSD limit the formation of carrots in regions containing BPD. These data also add support for mechanisms requiring the need for both dissociated BPD and TSD for carrot formation.

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15

Roy, Shyamal, Sönke Wille, Dan Mordehai, and Cynthia A. Volkert. "Investigating Nanoscale Contact Using AFM-Based Indentation and Molecular Dynamics Simulations." Metals 12, no. 3 (March 14, 2022): 489. http://dx.doi.org/10.3390/met12030489.

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In this work we study nanocontact plasticity in Au thin films using an atomic force microscope based indentation method with the goal of relating the changes in surface morphology to the dislocations created by deformation. This provides a rigorous test of our understanding of deformation and dislocation mechanisms in small volumes. A series of indentation experiments with increasing maximum load was performed. Distinct elastic and plastic regimes were identified in the force-displacement curves, and the corresponding residual imprints were measured. Transmission electron microscope based measured dislocation densities appear to be smaller than the densities expected from the measured residual indents. With the help of molecular dynamics simulations we show that dislocation nucleation and glide alone fail to explain the low dislocation density. Increasing the temperature of the simulations accelerates the rate of thermally activated processes and promotes motion and annihilation of dislocations under the indent while transferring material to the upper surface; dislocation density decreases in the plastic zone and material piles up around the indent. Finally, we discuss why a significant number of cross-slip events is expected beneath the indent under experimental conditions and the implications of this for work hardening during wear.

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16

Li, Miao Miao, Xiao Ping Su, De Shen Feng, Jian Long Zuo, Nan Li, and Xue Wu Wang. "The Study of Flower-Shaped Structure Dislocation in 4 Inch <100> Germanium Single Crystal." Materials Science Forum 685 (June 2011): 141–46. http://dx.doi.org/10.4028/www.scientific.net/msf.685.141.

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As the key component of single junction GaAs/Ge solar cells and GaAs/Ge solar cells, the quality of germanium single crystal affects the properties of space solar cell directly. The dislocation of germanium single crystals is the main impact factor on solar cells efficiency. Through measuring dislocation densities in the different positions of 4 inch <100> germanium single crystals produced by Czochralski method, we found that flower-shaped structure dislocations pattern was mainly caused by the inclusions. This paper briefly analyzed dislocations produced by inclusions, chemical etching pits method. SEM and EDS measurement methods were also employed to study the flower-shaped structure defects. A germanium single crystal with low dislocation density was obtained and the special defects were almost eliminated. The germanium single crystal with low dislocation density (PV) was obtained, which could meet the requirement of the GaAs/Ge solar cells.

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17

Zhang, Ming Yi, Min Zhong, Shuai Yuan, Jing Song Bai, and Ping Li. "Influence of Initial Defects on the Mechanical Properties of Single Crystal Copper: Discrete Dislocation Dynamics Study." Materials Science Forum 913 (February 2018): 627–35. http://dx.doi.org/10.4028/www.scientific.net/msf.913.627.

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In this paper, three dimensional discrete dislocation dynamics method was used to quantitatively investigate the influence of initial defects on mechanical response of single crystal copper. Both the irradiation defects (interstitial loops) and random dislocation lines with different densities are considered. The simulation results demonstrate that the yield strength of single crystal copper is higher with higher initial dislocation density and higher interstitial loop density. Dislocation density increases quickly by nucleation and multiplication and microbands are formed during plastic deformation when only the random dislocation lines are initially considered. Characteristics of microbands show excellent agreement with experiment results. Dislocation multiplication is suppressed in the presence of interstitial loops, and junctions and locks between dislocations and interstitial loops are formed. Dislocation density evolution shows fluctuation accompanied with strain-stress curve fluctuation.

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18

Porz, Lukas, Arne J. Klomp, Xufei Fang, Ning Li, Can Yildirim, Carsten Detlefs, Enrico Bruder, et al. "Dislocation-toughened ceramics." Materials Horizons 8, no. 5 (2021): 1528–37. http://dx.doi.org/10.1039/d0mh02033h.

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Dislocations are mobile at low temperatures in surprisingly many ceramics but sintering minimizes their densities. Enabling local plasticity by engineering a high dislocation density is a way to combat short cracks and toughen ceramics.

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19

Buzolin, Ricardo Henrique, Franz Miller Branco Ferraz, Michael Lasnik, Alfred Krumphals, and Maria Cecilia Poletti. "Improved Predictability of Microstructure Evolution during Hot Deformation of Titanium Alloys." Materials 13, no. 24 (December 12, 2020): 5678. http://dx.doi.org/10.3390/ma13245678.

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Two different mesoscale models based on dislocation reactions are developed and applied to predict both the flow stress and the microstructure evolution during the hot deformation of titanium alloys. Three distinct populations of dislocations, named mobile, immobile, and wall dislocations, describe the microstructure, together with the crystal misorientation and the densities of boundaries. A simple model consisting of production and recovery terms for the evolution of dislocations is compared with a comprehensive model that describes the reactions between different type of dislocations. Constitutive equations connect the microstructure evolution with the flow stresses. Both models consider the formation of a high angle grain boundary by continuous dynamic recrystallization due to progressive lattice rotation. The wall dislocation density evolution is calculated as a result of the subgrain size and boundary misorientation distribution evolutions. The developed models are applied to two near-β titanium alloys, Ti-5553 and Ti-17, and validated for use in hot compression experiments. The differences in the predictability between the developed models are discussed for the flow stress, dislocation densities and microstructure evolutions. Only the comprehensive model can predict the different reactions and their contributions to the evolution of mobile and immobile dislocation densities. The comprehensive model also allows for correlating the elastic strain rate with the softening and hardening kinetics. Despite those differences, the selection of the model used has a small influence on the overall prediction of the subgrain size and the fraction of high angle grain boundaries.

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20

Raphael, Johanna, Tedi Kujofsa, and J. E. Ayers. "Comparison of Buffer Layer Grading Approaches in InGaAs/GaAs (001)." International Journal of High Speed Electronics and Systems 29, no. 01n04 (March 2020): 2040002. http://dx.doi.org/10.1142/s0129156420400029.

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Metamorphic semiconductor devices often utilize compositionally-graded buffer layers for the accommodation of the lattice mismatch with controlled threading dislocation density and residual strain. Linear or step-graded buffers have been used extensively in these applications, but there are indications that sublinear, superlinear, S-graded, or overshoot graded structures could offer advantages in the control of defect densities. In this work we compare linear, step-graded, and nonlinear grading approaches in terms of the resulting strain and dislocations density profiles using a state-of-the-art model for strain relaxation and dislocation dynamics. We find that sublinear grading results in lower surface dislocation densities than either linear or superlinear grading approaches.

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21

Zhang, Y. J., Z. P. Wang, Y. Kuang, H. H. Gong, J. G. Hao, X. Y. Sun, F. F. Ren та ін. "Dislocation dynamics in α-Ga₂O₃ micropillars from selective-area epitaxy to epitaxial lateral overgrowth". Applied Physics Letters 120, № 12 (21 березня 2022): 121601. http://dx.doi.org/10.1063/5.0085367.

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Epitaxial lateral overgrowth (ELO) is an effective strategy to achieve metastable phased α-Ga2O3 with low dislocation densities, which is desirable for developing ultralow-loss and ultrahigh power devices, whereas the involved dislocation dynamics have not been fully exploited. In this Letter, we investigated the dislocation propagations and reactions in α-Ga2O3 micropillar arrays selectively grown by halide vapor phase epitaxy technique. Screw dislocations in α-Ga2O3 micropillars grown from the selective area epitaxy (SAE) to ELO mode exhibited an independent character with an average density of 4.5 × 106 cm−2 while the edge dislocation density was reduced to 5.3 × 108 cm−2. During the initial SAE process, the α-Ga2O3 hexagonal pyramid is developed with the observed inversion domains within the pillar cores. The successive epitaxial lateral overgrowth ELO facilitates the formation of inclined facets upon the SiO2 mask. Almost complete filtering of the underlying threading dislocation has been demonstrated in the ELO wings. Strong image forces induced by inclined free surfaces drive the propagation and reaction of threading dislocations until annihilation, which is well described by the dislocation-filtering model during the dynamic geometry transition of micropillars. These findings may pave the way for the success of the heteroepitaxy of low dislocation density α-Ga2O3 toward the development of high-performance power devices.

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22

Cai, Minglei, Tedi Kujofsa, Xinkang Chen, Md Tanvirul Islam, and John E. Ayers. "Interaction Length for Dislocations in Compositionally-Graded Heterostructures." International Journal of High Speed Electronics and Systems 27, no. 03n04 (September 2018): 1840022. http://dx.doi.org/10.1142/s0129156418400220.

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Several simple models have been developed for the threading dislocation behavior in heteroepitaxial semiconductor materials. Tachikawa and Yamaguchi [Appl. Phys. Lett., 56, 484 (1990)] and Romanov et al. [Appl. Phys. Lett., 69, 3342 (1996)] described models for the annihilation and coalescence of threading dislocations in uniform-composition layers, and Kujofsa et al. [J. Electron. Mater., 41, 2993 (2013)] extended the annihilation and coalescence model to compositionally-graded and multilayered structures by including the misfit dislocation-threading dislocation interactions. However, an important limitation of these previous models is that they involve empirical parameters. The goal of this work is to develop a predictive model for annihilation and coalescence of threading dislocations which is based on the dislocation interaction length Lint. In the first case if only in-plane glide is considered the interaction length is equal to the length of misfit dislocation segments while in the second case glide and climb are considered and the interaction length is a function of the distance from the interface, the length of misfit dislocations, and the density of the misfit dislocations. In either case the interaction length may be calculated using a model for dislocation flow. Knowledge of the dislocation interaction length allows predictive calculations of the threading dislocation densities in metamorphic device structures and is of great practical importance. Here we demonstrate the latter model based on glide and climb. Future work should compare the two models to determine which is more relevant to typical device heterostructures.

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23

Sun, Yue Jun, Oliver Brandt, and Klaus H. Ploog. "Photoluminescence intensity of GaN films with widely varying dislocation density." Journal of Materials Research 18, no. 5 (May 2003): 1247–50. http://dx.doi.org/10.1557/jmr.2003.0171.

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We investigated the impact of the presence of dislocations on room-temperature photoluminescence intensity in GaN films grown by molecular beam epitaxy. To determine both screw and edge dislocation densities, we employed x-ray diffraction in conjunction with a geometrical model, which relate the width of the respective reflections to the polar and azimuthal orientational spread. There is no direct dependence of the emission efficiency on the density of either type of dislocation in the samples under investigation. We conclude that dislocations are not the dominant nonradiative recombination centers for GaN grown by molecular beam epitaxy.

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24

Allen, Robert, Laszlo Toth, Andrew Oppedal, and Haitham El Kadiri. "Crystal Plasticity Modeling of Anisotropic Hardening and Texture Due to Dislocation Transmutation in Twinning." Materials 11, no. 10 (September 28, 2018): 1855. http://dx.doi.org/10.3390/ma11101855.

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In crystalline materials, dislocations are three-dimensional lattice distortions that systematically distort twin interfaces that they encounter. This results in dislocation dissociation events and changes in the atomic structure of the interface. The manner in which the interface distorts drive the product of the dissociation event, and consequently, the incident dislocation core and the magnitude and relative direction of the Burgers vector govern these slip-twin interaction phenomena. Recent characterization studies using transmission electron microscopy as well as advanced molecular dynamic simulations have shown that slip dislocations, whether striking or struck by a {10 1 ¯ 2} twin boundary, dissociate into a combination of twinning disconnections, interfacial disclinations (facets), jogs, and other types of dislocations engulfed inside the twin domains, called transmuted dislocations. While twinning disconnections were found to promote twin propagation, the dislocations incorporated inside the twin are of considerable importance to hardening and damage initiation as they more significantly obstruct slip dislocations accommodating plasticity of the twins. In this work, the dislocation transmutation event and its effect on hardening is captured using a dislocation density based hardening model contained in a visco-plastic self-consistent mean-field model. This is done by allowing the twins to increase their dislocation densities, not only by virtue of slip inside the twin, but also through dislocations that transmute from the parents as the twin volume fraction increases. A correspondence matrix rule is used to determine the type of converted dislocations while tracking and parameterizing their evolution. This hypothesis provides a modeling framework for capturing slip-twin interactions. The model is used to simulate the mechanical response of pure Mg and provides a more physically based approach for modeling stress-strain behavior.

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25

Liu, Hongguang, Jun Zhang, Xiang Xu, Yutong Qi, Zhechao Liu, and Wanhua Zhao. "Effects of Dislocation Density Evolution on Mechanical Behavior of OFHC Copper during High-Speed Machining." Materials 12, no. 15 (July 24, 2019): 2348. http://dx.doi.org/10.3390/ma12152348.

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This paper aims at investigating the change in material behavior induced by microstructure evolution during high-speed machining processes. Recently, high-speed machining has attracted quite a lot of interest from researchers due to its high efficiency and surface quality in machining large-scale components. However, the material behavior could change significantly at high-cutting speeds compared to the conventional cutting conditions, including their microstructure and t mechanical response. This is due to the basic physics of material at microscopic levels with high strain, high strain rates, and high temperatures. In this study, the dislocation density-related microstructure evolution process and mechanical behavior of OFHC (Oxygen-free high-conductivity) copper in high-speed machining with speeds ranging from 750 m/min to 3000 m/min are investigated. SEM (Scanning Electron Microscope) and advanced EBSD (Electron Backscattered Diffraction) techniques are used to obtain high-quality images of the microstructures and analyze the dislocation density and grain size evolution with different cutting speeds. Moreover, as material plasticity is induced by the motion of dislocations at micro-scales, a dislocation-density based (DDB) model is applied to predict strain-stress and microstructure information during the cutting process. The distributions of dislocation densities, both statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs), are obtained through simulation and experimentation, respectively. The results show that the fluctuation in the cutting forces at high cutting speeds is induced by the specific evolution and distribution of the dislocation density under high strain-rates, and the periodical distribution of sub-surface and fracture behavior during chip separation, which are also found to be influenced by the evolution of the dislocation density.

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26

Sato, Shigeo, Yohei Takahashi, Kazuaki Wagatsuma, and Shigeru Suzuki. "Characterization of aging behavior of precipitates and dislocations in copper-based alloys." Powder Diffraction 25, no. 2 (June 2010): 104–7. http://dx.doi.org/10.1154/1.3416942.

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The growth of precipitates in a deformed Cu–Ni–Si alloy with an aging treatment and the rearrangement of dislocations were investigated using small-angle X-ray scattering method and XRD line-profile analysis. The small-angle X-ray scattering method was used for characterizing the growth behavior of the precipitates. The results showed that the precipitates grew gradually to a few nanometers in radius when aged under the condition that the alloy exhibited a maximum of the hardness due to precipitation hardening. The growth rate rose from the onset of the overaging, where the hardness started to decrease. The line-profile analysis of copper-based alloy diffraction peaks using modified Williamson–Hall and modified Warren–Averbach procedures yielded a variation in the dislocation densities of the alloy as a function of the aging time. The dislocation density of the alloy before the aging treatment was estimated to be 1.7×1015 m−2 and its high value was held up to the peak-aging time. With the onset of the overaging, however, the dislocation density distinctly decreased by about 1 order of magnitude indicating that a large amount of the dislocations rearranged to release the alloy from the high dislocation-density state. The results suggest that the massive rearrangement of dislocations was accompanied with coarsening of the precipitates.

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27

Merriman, C. C., and David P. Field. "Observations of Dislocation Structure in AA 7050 by EBSD." Materials Science Forum 702-703 (December 2011): 493–98. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.493.

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During and after plastic deformation of metals, dislocations tend to evolve into generally well-defined structures that may include tangles, bands, cell walls, and various additional features. Observation of these structures by electron backscatter diffraction is only accomplished by analysis of changes in orientation from one position to the next. Excess (or geometrically necessary) dislocation densities can be inferred from 2D measurements or obtained directly from 3D measurements as indicated by Nye’s dislocation density tensor. Evolution of excess dislocation densities was measured for a split channel die specimen of aluminum alloy 7050 in the T7451 temper. Densities evolved by a factor or 1.6 for compressive deformations of 15%.

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28

Bertoni, Mariana I., Clémence Colin, and Tonio Buonassisi. "Dislocation Engineering in Multicrystalline Silicon." Solid State Phenomena 156-158 (October 2009): 11–18. http://dx.doi.org/10.4028/www.scientific.net/ssp.156-158.11.

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Dislocations are known to be among the most deleterious performance-limiting defects in multicrystalline silicon (mc-Si) based solar cells. In this work, we propose a method to remove dislocations based on a high temperature treatment. Dislocation density reductions of >95% are achieved in commercial ribbon silicon with a double-sided silicon nitride coating via high temperature annealing under ambient conditions. The dislocation density reduction follows temperature-dependent and time-dependent models developed by Kuhlmann et al. for the annealing of dislocations in face-centered cubic metals. It is believed that higher annealing temperatures (>1170°C) allow dislocation movement unconstrained by crystallographic glide planes, leading to pairwise dislocation annihilation within minutes.

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29

Petelina, Yulia, Svetlana Kolupaeva, Konstantin A. Polosukhin, and Aleksander Petelin. "Influence of the Dislocation Density on the Expansion Dynamics of the Crystallographic Slip Zone along Screw Orientations in Aluminum and Copper." Key Engineering Materials 683 (February 2016): 136–41. http://dx.doi.org/10.4028/www.scientific.net/kem.683.136.

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Crystallographic slip is one of key mechanisms determining plastic form change of crystalline solids. Despite a large amount of works done on the subject, crystallographic slip is a very difficult subject to study. Significant progress in the study of the crystallographic slip process is possible only with the use of a set of different methods: experimental methods, methods of mathematical modeling and simulation. The paper presents a modification mathematical expansion model of closed dislocations emitted by one dislocation source with takes into account the elastic interaction force among all dislocations of the forming dislocation pile-up. The model takes into account the Peach-Koehler forces, lattice, impurity, and dislocation friction, linear tension, viscous deceleration, and the intensity of generation of point defects beyond jogs on the dislocation, as well as the elastic interaction force among all dislocations of the forming dislocation pile-up. The analysis of the study results on the expansion dynamics of the dislocation loop along the screw orientation on copper and aluminum with varying of the dislocation density from 3×1011 m−2 to 1012 m−2 is carried out. It is established that the length and the path time of the screw dislocation, as well as the number of dislocations emitted by the dislocation source, essentially depend on the density of dislocations. The dependence of the current radius, velocity, and kinetic energy of the screw dislocation on the path time and the dependence of the current velocity and the kinetic energy of the first screw dislocation emitted by the dislocation source on its current radius are described.

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30

ZHAI, Z. Y., X. Z. LI, S. S. ZHI, X. S. WU, J. H. HAO, and J. GAO. "DISLOCATION DENSITY IN SrTiO3 FILM GROWN ON DyScO3 BY PULSE LASER ABLATION." Surface Review and Letters 14, no. 04 (August 2007): 779–82. http://dx.doi.org/10.1142/s0218625x07010251.

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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.

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31

Ohmori, Noriko, Tomonori Uchimaru, Hiroyuki Fujimori, Jun Komiyama, Yoshihisa Abe, and Shunichi Suzuki. "Characterization of Dislocations in GaN Thin Film and GaN/AlN Multilayer." Materials Science Forum 725 (July 2012): 75–78. http://dx.doi.org/10.4028/www.scientific.net/msf.725.75.

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The dislocations in GaN thin film with GaN/AlN multilayer (ML) as the buffer layer were evaluated using transmission electron microscopy. A high density of dislocations parallel to the GaN/ML interface and a sudden decrease in the dislocation density at the GaN/ML interface were found. Dislocation propagation in the direction parallel to the GaN/ML interface by turning horizontally on the GaN/ML interface is considered to be effective in decreasing the dislocation density at the top layer of GaN.

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32

Nakagawa, Koutarou, Momoki Hayashi, Kozue Takano-Satoh, Hirotaka Matsunaga, Hiroyuki Mori, Kazunari Maki, Yusuke Onuki, Shigeru Suzuki, and Shigeo Sato. "Characterization of Dislocation Rearrangement in FCC Metals during Work Hardening Using X-ray Diffraction Line-Profile Analysis." Quantum Beam Science 4, no. 4 (October 11, 2020): 36. http://dx.doi.org/10.3390/qubs4040036.

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Multiplication and rearrangement of dislocations in face-centered cubic (FCC) metals during tensile deformation are affected by grain size, stacking fault energy (SFE), and solute elements. X-ray diffraction (XRD) line-profile analysis can evaluate the dislocation density (ρ) and dislocation arrangement (M) from the strength of the interaction between dislocations. However, the relationship between M and ρ has not been thoroughly addressed. In this study, multiplication and rearrangement of dislocations in FCC metals during tensile deformation was evaluated by XRD line-profile analysis. Furthermore, the effects of grain size, SFE, and solute elements on the extent of dislocation rearrangement were evaluated with varying M values during tensile deformation. M decreased as the dislocation density increased. By contrast, grain size and SFE did not exhibit a significant influence on the obtained M values. The influence of solute species and concentration of solute elements on M changes were also determined. In addition, the relationship between dislocation substructures and M for tensile deformed metals were also explained. Dislocations were loosely distributed at M > 1, and cell walls gradually formed by gathering dislocations at M < 1. While cell walls became thicker with decreasing M in metals with low stacking fault energy, thin cell walls with high dislocation density formed for an M value of 0.3 in metals with high stacking fault energy.

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33

Mughrabi, Haël, and Bernhard Obst. "Misorientations and geometrically necessary dislocations in deformed copper crystals: A microstructural analysis of X-ray rocking curves." International Journal of Materials Research 96, no. 7 (July 1, 2005): 688–97. http://dx.doi.org/10.1515/ijmr-2005-0122.

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Abstract In this study, the deformation-induced misorientations that are typically found in face-centred cubic single crystals deformed in single slip into stage II (and early stage III) of the work-hardening curve are discussed with respect to the experimentally observed broadening of X-ray rocking curves. By making use of well-established empirical relationships between characteristic features of the microstructure and the flow stress, some of the ambiguities of earlier interpretations of rocking curves could be avoided, and relationships between the half-widths of the rocking curves, the density of geometrically necessary dislocations, and the flow stress could be derived for both the tilt misorientations due to the kink bands lying perpendicular to the primary Burgers vector and the twist misorientations originating from the dislocation networks (grids, sheets) lying parallel to the primary glide plane. An evaluation of largely unpublished experimental rocking-curve data obtained on different crystallographic sections of deformed copper single crystals yielded a linear relationship between the broadening of the rocking curves and the flow stress. In terms of the predictions of the model developed, this implies that the ratio of the density of the geometrically necessary dislocations (that are responsible for the misorientations) to the total dislocation density remains constant during deformation, at least up to flow stresses of about 50 MPa. The absolute densities of the geometrically necessary dislocations are found to be a small fraction (at most ca. 5%) of the total dislocation densities. In terms of the evolution laws of deformation-induced dislocation boundaries proposed in the literature, it is concluded that both kink bands and grids/ sheets follow the characteristics of so-called geometrically necessary boundaries.

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34

Anzalone, Ruggero, Nicolò Piluso, Andrea Severino, Simona Lorenti, Giuseppe Arena, and Salvo Coffa. "Dislocations Propagation Study Trough High-Resolution 4H-SiC Substrate Mapping." Materials Science Forum 963 (July 2019): 276–79. http://dx.doi.org/10.4028/www.scientific.net/msf.963.276.

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In this work a deep investigation of the dislocation on 4H-SiC substrate has been shown. The dislocation intersecting the surface were enhanced by KOH etching at 500 deg. C. performed on whole 6 inches substrate. A comparison between basal plane dislocations and threading screw dislocations in the substrate with the defects in the epitaxial layer (mainly stacking faults and carrots) was performed. The comparison between shows a correlation between basal plane dislocations density and stacking faults density maps.

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35

Raghothamachar, Balaji, Yu Yang, Rafael Dalmau, Baxter Moody, H. Spalding Craft, Raoul Schlesser, Michael Dudley, and Zlatko Sitar. "Defect Generation Mechanisms in PVT-Grown AlN Single Crystal Boules." Materials Science Forum 740-742 (January 2013): 91–94. http://dx.doi.org/10.4028/www.scientific.net/msf.740-742.91.

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A systematic study on the density and distribution of extended defects in a typical single crystal AlN boule grown by the physical vapor transport (PVT) method has been carried out in order to gain a detailed understanding of the formation of defects such as dislocations and low angle grain boundaries (LAGBs). Boule surface studies reveal that LAGBs are nucleated during initial stages of growth and propagate to the end of growth. Basal plane dislocations (BPDs) are generated during growth due to thermal gradient stresses. Higher BPD densities are found near the LAGBs at the boule edges due to additional stresses from constrained growth. Threading edge dislocations (TEDs) are typically replicated from the seed, and LAGBs composed of arrays of threading dislocation walls are formed to accommodate the c-axis rotation between different groups of threading screw dislocation (TSD) mediated growth centers.

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36

Wang, Ding, Ping Wang, Shubham Mondal, Yixin Xiao, Mingtao Hu, and Zetian Mi. "Impact of dislocation density on the ferroelectric properties of ScAlN grown by molecular beam epitaxy." Applied Physics Letters 121, no. 4 (July 25, 2022): 042108. http://dx.doi.org/10.1063/5.0099913.

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We report on the effect of dislocation density on the ferroelectric properties of single-crystalline ScAlN thin films grown by molecular beam epitaxy. Wurtzite phase and atomically smooth ScAlN films have been grown on bulk GaN, GaN on sapphire, and GaN on Si substrates with dislocation densities ranging from ∼107 to 1010 cm−2. Despite the significant difference in dislocation density, ferroelectricity is observed in all three samples. The presence of high densities of dislocations, however, results in enhanced asymmetric P–E loops and overestimated remnant polarization values. Further measurements show that the leakage current and breakdown strength can be improved with decreasing dislocation density. Detailed studies suggest that trapping/detrapping assisted transport is the main leakage mechanism in epitaxial ferroelectric ScAlN films. This work sheds light on the essential material quality considerations for tuning the ferroelectric property of ScAlN toward integration with mainstream semiconductor platforms, e.g., Si, and paves the way for next-generation electronics, optoelectronics, and piezoelectronics.

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37

Starenchenko, Vladimir, Dmitrii Cherepanov, Raisa Kurinnaya, Marina Zgolich, and Olga Selivanikova. "The Influence of Dislocation Junctions on Accumulation of Dislocations in Strained FCC – Single Crystals." Advanced Materials Research 1013 (October 2014): 272–79. http://dx.doi.org/10.4028/www.scientific.net/amr.1013.272.

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Dislocation junctions, formed as a result of dislocation reactions, affect the plastic strain process, at least, for two reasons. First of all, junctions serve as barriers to shear-forming dislocations and restrict their path, therefore, the size of the shear zone. Sizes of the shear zone are determined by the density of reacting dislocations in non-coplanar slip systems, forming long enough barriers in the form of dislocation junctions. Secondly, non-breaking dislocation junctions are accumulated inside the shear zone, which leads to an increase in the intensity of the dislocation density accumulation.The present work is devoted to the study of the influence of dislocation junctions on accumulation of the density of dislocation debris (debris junctions) due to formation of stable junctions. For this purpose, the probability density function of lengths in non-breaking junctions is calculated. The model of dislocation interactions, built by the authors of the paper for FCC single crystals, is used.

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38

Marshall, A. F., D. B. Aubertine, W. D. Nix, and P. C. McIntyre. "Misfit dislocation dissociation and Lomer formation in low mismatch SiGe/Si heterostructures." Journal of Materials Research 20, no. 2 (February 2005): 447–55. http://dx.doi.org/10.1557/jmr.2005.0065.

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Using transmission electron microscopy we observe the dissociation of 60° misfit dislocations at the interface of SiGe/Si multilayers, extending into the substrate for distances of 5.0–7.5 nm. Analysis using elasticity theory shows that this dissociationis the equilibrium configuration for individual 60° misfit dislocations, as it is for 60° mixed dislocations in bulk Si, and that the compressively strained multilayer film serves mainly to position the partial dislocations and stacking fault with respect to the free surface. We observe both undissociated 60° and Lomer edge dislocations after annealing, and conclude that these result from dislocation climb in the interface. Since the dislocations move off their slip plane during climb, they cannot remain dissociated. Significant climb and Lomer dislocation formation for these low misfit layers is observed at temperatures above 850 °C and for samples with a high initial dislocation density, such as found in thicker as-grown samples. The dislocation configuration formed during annealing is distinct from that reported to form during growth of higher mismatch films: the Lomer dislocations tend to be segmented, with the segments connected by perfect 60° dislocations.

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39

Wang, Xiaona, Haibin Zhang, Shinong Yan, Yongmei Zhang, Xiaolin Tian, Dunwei Peng, and Yuhong Zhao. "The Response Mechanism of Crystal Orientation to Grain Boundary Dislocation under Uniaxial Strain: A Phase-Field-Crystal Study." Metals 12, no. 5 (April 21, 2022): 712. http://dx.doi.org/10.3390/met12050712.

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An exploration of dislocation microstructure evolution with different misorientation angles was performed using phase field crystal method (PFC). The microcosmic evolution process of grain boundaries under external stress, as well as the corresponding energy curve and stress–strain curve, are analyzed. The relationship between the misorientation angle and the dislocations emission frequency is discussed. Three forms of dislocations reaction on the evolution process of 6°and 10° are analyzed in detail, which are respectively type I semi-annihilation, type II semi-annihilationand full-annihilation. Among them, the nature of type I semi-annihilation is a combination of dislocation and a single edge dislocation reaction with a single edge dislocation left. The essence of type II semi-annihilation is a pair of dislocation and the other pair of dislocation reaction leaving two edge dislocations. The essence of full-annihilation is that two pairs of dislocations or single edge dislocations with opposite Burger vectors react with each other and the distortion area disappears. When the misorientation angle is 10°, the dislocation reaction and the dislocation motion ability of the system are stronger than 6°. The peak of the energy curve is related to the number of dislocation proliferations in the evolution process. An emission frequency and average density of dislocations of 10° is greater than 6°. The causes of plastic deformation are revealed to a certain extent by stress–strain curves.

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40

Strunk, Horst P. "Origination and Properties of Dislocations in Thin Film Nitrides." Solid State Phenomena 131-133 (October 2007): 39–46. http://dx.doi.org/10.4028/www.scientific.net/ssp.131-133.39.

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Epitaxial group-III nitride films, although in single crystalline form, contain still a large number of threading dislocations. These set limits to performance and lifetime of devices, notably to high power structures like lasers. The strategy in material development was and will be (at least until lattice-matched substrates become available) to reduce the dislocation densities. The present contribution elaborates on possible dislocation origination mechanisms that determine the population of dislocations in the epitaxial layers. These mechanisms can be controlled to a certain degree by proper deposition procedures. The achieved dislocation populations then determine the processes that can reduce the dislocation densities during growth of the epitaxial layers. The mutual annihilation of threading dislocations is rather efficient although affected by the glide properties of the growing epitaxial crystal and the thermal stresses during the cooling down after growth.

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41

Lu, Qi, Andrew Marshall, and Anthony Krier. "Metamorphic Integration of GaInAsSb Material on GaAs Substrates for Light Emitting Device Applications." Materials 12, no. 11 (May 29, 2019): 1743. http://dx.doi.org/10.3390/ma12111743.

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The GaInAsSb material has been conventionally grown on lattice-matched GaSb substrates. In this work, we transplanted this material onto the GaAs substrates in molecular beam epitaxy (MBE). The threading dislocations (TDs) originating from the large lattice mismatch were efficiently suppressed by a novel metamorphic buffer layer design, which included the interfacial misfit (IMF) arrays at the GaSb/GaAs interface and strained GaInSb/GaSb multi-quantum wells (MQWs) acting as dislocation filtering layers (DFLs). Cross-sectional transmission electron microscopy (TEM) images revealed that a large part of the dislocations was bonded on the GaAs/GaSb interface due to the IMF arrays, and the four repetitions of the DFL regions can block most of the remaining threading dislocations. Etch pit density (EPD) measurements indicated that the dislocation density in the GaInAsSb material on top of the buffer layer was reduced to the order of 106 /cm2, which was among the lowest for this compound material grown on GaAs. The light emitting diodes (LEDs) based on the GaInAsSb P-N structures on GaAs exhibited strong electro-luminescence (EL) in the 2.0–2.5 µm range. The successful metamorphic growth of GaInAsSb on GaAs with low dislocation densities paved the way for the integration of various GaInAsSb based light emitting devices on the more cost-effective GaAs platform.

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42

Yang, Mino, Chong-Don Kim, Hee-Goo Kim, and Cheol-Woong Yang. "Spatial Distribution of Dislocations in Relation to a Substructure in High-Quality GaN Film." Microscopy and Microanalysis 19, S5 (August 2013): 127–30. http://dx.doi.org/10.1017/s1431927613012488.

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AbstractThe dislocation distribution of high-quality single-crystal gallium nitride (GaN) films grown by the hybrid vapor phase epitaxy was analyzed. This study examined the domain structure of GaN from the dislocation distribution on the macroscale by optical microscopy. The surface structure of GaN consisted of domains with microcolumns as the substructure. The inner domains contained a lower density of dislocations but a large number of these dislocations were observed along the domain boundaries. The existence of a domain boundary structure doubly increased the total dislocation density.

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43

Chamma, Layal, Jean-Marc Pipard, Artem Arlazarov, Thiebaud Richeton, Jean-Sébastien Lecomte, and Stéphane Berbenni. "A combined EBSD/nanoindentation study of dislocation density gradients near grain boundaries in a ferritic steel." Matériaux & Techniques 110, no. 2 (2022): 203. http://dx.doi.org/10.1051/mattech/2022005.

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Microstructural internal lengths play an important role on the local and macroscopic mechanical behaviors of steels. In this study, the dislocation density gradients near grain boundaries in a ferritic steel are investigated using SEM/EBSD together with instrumented nanoindentation for undeformed and pre-deformed aluminum-killed steels (Al-k) at 3% and 18% tensile plastic strains. The effect of the distance to grain boundaries on Geometrically Necessary Dislocations (GND) densities is first determined by analyzing orientation gradients from 2D-EBSD maps. Then, nanohardness measurements are performed in the vicinity of grain boundaries. Data analyses show a clear correlation between the spatial gradients of GND density and the ones of nanohardness. Using a mechanistic model, the total dislocation densities are estimated from the measured nanohardness values. From both GND and total dislocation density profiles, the value of an internal length, denoted λ, is estimated from the analysis of dislocation density gradients near grain boundaries. At the end, the capabilities of 2D-EBSD and nanoindentation methods to assess this value are discussed.

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44

Chamma, Layal, Jean-Marc Pipard, Artem Arlazarov, Thiebaud Richeton, Jean-Sébastien Lecomte, and Stéphane Berbenni. "A combined EBSD/nanoindentation study of dislocation density gradients near grain boundaries in a ferritic steel." Matériaux & Techniques 110, no. 2 (2022): 203. http://dx.doi.org/10.1051/mattech/2022005.

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Анотація:

Microstructural internal lengths play an important role on the local and macroscopic mechanical behaviors of steels. In this study, the dislocation density gradients near grain boundaries in a ferritic steel are investigated using SEM/EBSD together with instrumented nanoindentation for undeformed and pre-deformed aluminum-killed steels (Al-k) at 3% and 18% tensile plastic strains. The effect of the distance to grain boundaries on Geometrically Necessary Dislocations (GND) densities is first determined by analyzing orientation gradients from 2D-EBSD maps. Then, nanohardness measurements are performed in the vicinity of grain boundaries. Data analyses show a clear correlation between the spatial gradients of GND density and the ones of nanohardness. Using a mechanistic model, the total dislocation densities are estimated from the measured nanohardness values. From both GND and total dislocation density profiles, the value of an internal length, denoted λ, is estimated from the analysis of dislocation density gradients near grain boundaries. At the end, the capabilities of 2D-EBSD and nanoindentation methods to assess this value are discussed.

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45

Chamma, Layal, Jean-Marc Pipard, Artem Arlazarov, Thiebaud Richeton, Jean-Sébastien Lecomte, and Stéphane Berbenni. "A combined EBSD/nanoindentation study of dislocation density gradients near grain boundaries in a ferritic steel." Matériaux & Techniques 110, no. 2 (2022): 203. http://dx.doi.org/10.1051/mattech/2022005.

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Анотація:

Microstructural internal lengths play an important role on the local and macroscopic mechanical behaviors of steels. In this study, the dislocation density gradients near grain boundaries in a ferritic steel are investigated using SEM/EBSD together with instrumented nanoindentation for undeformed and pre-deformed aluminum-killed steels (Al-k) at 3% and 18% tensile plastic strains. The effect of the distance to grain boundaries on Geometrically Necessary Dislocations (GND) densities is first determined by analyzing orientation gradients from 2D-EBSD maps. Then, nanohardness measurements are performed in the vicinity of grain boundaries. Data analyses show a clear correlation between the spatial gradients of GND density and the ones of nanohardness. Using a mechanistic model, the total dislocation densities are estimated from the measured nanohardness values. From both GND and total dislocation density profiles, the value of an internal length, denoted λ, is estimated from the analysis of dislocation density gradients near grain boundaries. At the end, the capabilities of 2D-EBSD and nanoindentation methods to assess this value are discussed.

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46

Hirokazu, Fujiwara, Masaki Konishi, T. Ohnishi, T. Nakamura, Kimimori Hamada, T. Katsuno, Y. Watanabe, et al. "Reverse Electrical Characteristics of 4H-SiC JBS Diodes Fabricated on In-House Substrate with Low Threading Dislocation Density." Materials Science Forum 679-680 (March 2011): 694–97. http://dx.doi.org/10.4028/www.scientific.net/msf.679-680.694.

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The impacts of threading dislocations, surface defects, donor concentration, and schottky Schottky barrier height on the reverse IV characteristic of silicon carbide (SiC) junction barrier schottky Schottky (JBS) diodes were investigated. The 100 A JBS diodes were fabricated on 4H-SiC 3-inch N-type wafers with two types of threading dislocation density. The typical densities are were 0.2×104 and 3.8×104 cm-2, respectively. The improvement of vIt was found that variations in the leakage current and the high yield of large area JBS diodes werecould be were obtained improved by using a wafer with a low threading dislocation density. In the range of low leakage current, the investigation shows showed a correlation between leakage current and threading dislocation density.

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47

Hurski, L. I. "Deformed and stressed states of materials at the rolling of three layer stacks, dislocation structure of inner layer – nickel foil." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 66, no. 3 (October 12, 2021): 270–79. http://dx.doi.org/10.29235/1561-8358-2021-66-3-270-279.

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The deformed and stressed states during rolling of a three-layer stack from various materials with a nickel foil inner layer are considered. The technique of determining the density of dislocations is described. The data about the inﬂuence of deformation conditions on the distribution and density of dislocations during rolling of nickel foil in various stacks are presented, including the registration or determination of the dislocation structure of nickel foil before deformation and at various degrees of deformation. It is shown that the mechanical scheme of deformation of the inner layer of the stack, namely, the deformation of the nickel foil by non-uniform compression with shear, has a decisive inﬂuence on the development of the dislocation structure and properties. It is established that the dislocation density is determined not only by the degree of deformation, but also by a scheme of the deformed and stressed state of matter, and for the case of shear deformation with increasing degree of deformation the dislocation density increases more rapidly than in the case of tensile strain or compression without shear; the result of shear deformation is a signiﬁcant reﬁnement of the structure of materials: with increasing degree of plastic deformation of the material a three-dimensional cellular network of dislocation is formed, wherein the borders of cells are formed by tangles of dislocations. With increasing degree of deformation, the density of dislocations at the cell boundaries increases, and the size of the cells decreases; in this case, the areas inside the cells of the dislocation network are always free of dislocations. The obtained results allow recommending the schemes with shear deformation for new promising processes of production of materials with unique properties.

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48

Jóni, Bertalan, Talal Al-Samman, Sandip Ghosh Chowdhury, Gábor Csiszár, and Tamás Ungár. "Dislocation densities and prevailing slip-system types determined by X-ray line profile analysis in a textured AZ31 magnesium alloy deformed at different temperatures." Journal of Applied Crystallography 46, no. 1 (January 17, 2013): 55–62. http://dx.doi.org/10.1107/s0021889812046705.

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Tension experiments were carried out at room temperature, 473 K and 673 K on AZ31-type extruded magnesium alloy samples. The tensile deformation has almost no effect on the typical extrusion texture at any of the investigated temperatures. X-ray diffraction patterns provided by a high-angular-resolution diffractometer were analyzed for the dislocation density and slip activity after deformation to fracture. The diffraction peaks were sorted into two groups corresponding either to the major or to the random texture components in the specimen. The two groups of reflections were evaluated simultaneously as if the two texture components were two different phases. The dislocation densities in the major texture components are found to be always larger than those in the randomly oriented grain populations. The overwhelming fraction of dislocations prevailing in the samples is found to be of 〈a〉 type, with a smaller fraction of 〈c + a〉-type dislocations. The fraction of 〈c〉-type dislocations is always obtained to be zero within experimental error.

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49

Sato, Michihiro, Tetsuya Ohashi, Takuya Maruizumi, and Isao Kitagawa. "Crystal Plasticity Analysis of Thermal Deformation and Dislocation Accumulation in ULSI Cells." Key Engineering Materials 324-325 (November 2006): 1035–38. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.1035.

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Thermal stress, plastic slip deformation and accumulation of dislocations in shallow trench isolation (STI) type ULSI devices when the temperature drops from 1000 し to room temperature are analyzed by a crystal plasticity analysis cord. The results show that dislocation accumulation takes place at the temperature range over 800 し, and the difference of 6 MPa in the lattice friction stress at 1000 し!causes increase of dislocation density more than 1.6 times. Dislocations generate and accumulate at the shoulder part of the device area and bottom corners of the trench. Dislocations are categorized into two groups. In one group, dislocation lines are mostly straight and parallel to the trench direction, and in the other group, dislocations make half loop type structure. Possibilities for the suppression of dislocation accumulation through control of lattice friction stress at high temperature region are discussed.

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50

Bakke, K., and F. Moraes. "A geometric approach to dislocation densities in semiconductors." Modern Physics Letters B 28, no. 15 (June 17, 2014): 1450124. http://dx.doi.org/10.1142/s0217984914501243.

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Dislocation densities threading semiconductor crystals are a problem for device developers. Among the issues presented by the defect density is the appearance of the so-called shallow levels. In this work, we introduce a geometric model to explain the origin of the observed shallow levels. We show that a uniform distribution of screw dislocations acts as an effective uniform magnetic field which yields electronic bound states even in the presence of a repulsive Coulomb-like potential. This introduces energy levels within the band gap, increasing the carrier concentration in the region threaded by the dislocation density and adding additional recombination paths other than the near band-edge recombination. Our results suggest that one might use a magnetic field to destroy the dislocation density bound states and therefore minimize its effects on the charge carriers.

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