Papers by Keyword: Edge Dislocation

Abstract: 4H-SiC homo-epitaxial film was grown by adding HCl gas with a high Cl/Si ratio in CVD process, and defect formation and origin of the defect were investigated by confocal differential interference contrast (CDIC) microscope, PL imaging and normal differential interference contrast (DIC) microscope. It was found that a large number of large bumps are formed on the film grown at a high Cl/Si ratio of 30, and a large number of PL defects on bare substrate before the film growth are also observed. Coordinates where the bumps on the film are observed were good agreement with those where the PL defects on the bare substrate are observed. An etch pit sample on reproduced substrate from which epitaxial film was removed was fabricated by etching process using molten KOH+Na₂O₂, and some types of etch pits which might be originated from threading edge dislocations (TEDs), threading screw dislocations (TSDs) and basal plane dislocations (BPDs) in the substrate were observed. The coordinates where the etch pits on the reproduced substrate are observed were also good agreement with those where the bumps on the epitaxial film are observed. Therefore, it was clarified that a large number of the bumps abnormally grown on the epitaxial film are originated from the dislocations in the substrate.

Abstract: The energy characteristics of interaction of hydrogen impurity with ½<110> edge dislocation in Pd and Ni were calculated by the method of molecular dynamics. It is shown that the dislocation is effective trap for hydrogen. At the same time the dislocation jogs increases its sorption capacity with respect to hydrogen, but reduces the diffusion mobility of hydrogen along the dislocation. The diffusion of hydrogen atoms in the dislocation region occurs mainly along the dislocation core. The energy of hydrogen migration along the dislocation, as our calculations have shown, is almost two times lower than in a defect-free crystal.

Abstract: The experiments have emphasized that additionally introduced impurities of Fe and Pb ions are relevant to the initiation of slow and explosive decomposition of silver azide crystals by the external electric field and UV irradiation. External gas release was used for research purpose. Test-sensitivity is 10⁻¹² mole. Time-to-explosion was measured by a stop watch. It’s been found out that the reaction of slow decomposition in silver azide under the action of electric field turns into explosion faster in samples with the additionally introduced impurities. The samples with additionally introduced Fe are the most explosive ones (time-to-explosion 3 minutes). The authors have assumed that external influence can generate non-equilibrium charge carriers (holes), which become localized on cationic vacancies and support formation of reactive sites. As soon as cut off concentration of these sites is reached, the solid-phase chain reaction turns into explosion. The growing concentration of impurity influences on the number of reactive sites, making their concentration critical. In view of the results obtained in experiments a procedure for monitoring the decomposition of crystals is suggested, which necessitates additional introduction of Fe and Pb ions.

Abstract: In this work the behaviour of edge 1/2<111>{110} and screw 1/2<111>{112} dislocations were investigated by the method of molecular dynamics. The results of calculations show that molecular dynamics with used interatimic potential are able to properly describe the dislocation behavior. Two regimes of dislocation movement in molybdenum are shown to exist: thermo-activated and viscous regimes. Obtained results of dislocation mobility was fitted using the dislocation mobility law.

Abstract: Compared to perfect crystal lattice, typical edge dislocation structure has been modeled by quantum chemistry simulation in order to analyze the influence of crystal structure defects on removal process in atmospheric pressure plasma polishing (APPP). The Partial density of states (PDOS), number of states, average number of bonding electrons and energy have been calculated and analyzed further for these models. The analysis results reveal that silicon crystal with edge dislocation can be etched more easily than that of perfect crystal lattice. It is also found that the removal rate of sample with higher dislocation density is larger than that of lower dislocation density in the same experiment conditions. Thus, theoretical simulation demonstrates that structure dislocation is helpful for raising the etching rate, which accords well with testifying experiments results. But maybe structure dislocation could deteriorate surface roughness to some extent in initial stage of machining, as the dislocation structure is usually etched unevenly, although this is just a transition period.

Abstract: The second phase nucleation and precipitation around an edge dislocation are studied using phase field method. A new free energy function including the elastic strain energy is established to describe the dislocation interaction with the solute. The results give the distribution of strain field of dislocation and show the precipitates grow up according to the power growth law with the index 2. The simulated results are in good agreement with that of theory of non-uniform nucleation.

Abstract: The second phase nucleation and precipitation around the edge dislocation are studied using phase-field method. A new free energy function is established. The simulation results are in good agreement with that of theory of dislocation and theory of non-uniform nucleation.

Abstract: A model for the nucleation and growth processes of Sn whisker is offered. High density of localized screw dislocations by deformation form the dense spiral steps of atomic scale on Sn surface. The spiral steps would induce the nucleation of Sn whisker. Edge dislocations localized at the same region where the dense screw dislocations exist supply Sn atoms to Sn whisker through pipe diffusion. Both screw and edge dislocations would bend along almost one direction, namely, to relax the external shear stress. The image force also helps to bend the dislocations perpendicular to the whisker side-surface. The bending of dislocations at root of whisker leads the bend of whisker. The pipe diffusion of Sn atoms through edge dislocations from bulk Sn toward whisker is suppressed at the bent part of edge dislocation, resulting in release of Sn atoms inside whisker and leading to the growth of whisker near its root.

Abstract: Threading edge dislocations (TEDs) in a 4H-SiC epitaxial layer are investigated using high-resolution synchrotron topography. Six types of TED image are confirmed to correspond to the Burgers vector directions by a comparison of computer simulated images and observed topography images in crystal boundaries. Using a mapping method, a wide spatial distribution of the six types of TED is examined in a quarter section of a 2-inch wafer.

Abstract: The defects in crystalline materials significantly affect the fracture behaviors. In this paper molecular dynamics (MD) model using a potential of embedded atom method (EAM) has been developed to investigate the effect of the major crystalline defects, stacking fault and edge dislocation, on the crack propagation in Fe crystal. Six cases with different locations of stacking fault and edge dislocation have been studied. The strain distribution in lattice aggregate was heterogeneous. The dislocations were observed slipping along directions [100] and [-100] on the plane (100). Simulation results showed that the location of the stacking fault and edge dislocation significantly influenced the crack propagation speed.