Dislocations analysis

Elsworth, D. 1991. Dislocation analysis of penetration in saturated porous media. Journal of the Engineering Mechanics. Vol. 117. No. 2. 391-408. 

Long. H., Elsworth, D. Flemings, P.B. 2003. Composite dislocation analysis of piezoprobe penetration, (in preparation). J. Geophys. Res. 

Self-diffusion of Hg was studied, using radiotracers, at between 250 and 400C. The diffusion profiles were found to have 2 components, and contact autoradiography was used to relate the tail component of bulk samples to short-circuit diffusion via dislocation arrays. A dislocation analysis was used to characterize the diffusion tails and to estimate the Hg diffusion coefficient within the defect structure. The temperature variation of the lattice diffusion coefficient was measured under a saturated Hg partial pressure and was found to obey the equation ... 

Nicola, L., Van der Giessen, E. and Needleman, A. (2003), Discrete dislocation analysis of size effects in thin films, Acta Materialia,. ... 

The first TEM studies of defects in minerals were mostly carried out on layer-structured crystals that could easily be cleaved to electron transparent thicknesses. These included mica [33], graphite [34], molybdenite [35,36], and talc [37]. The study of dislocation networks in talc [38] is an early milestone in dislocation analysis. Thereafter, the ion-rmllmg method (and, more recently, the FIB (focused ion beam) technique) made it possible to investigate dislocations and other defects in a wide range of minerals, crustal rocks, and extraterrestrial materials. 

To answer questions regarding dislocation multiplication in Mg-doped LiF single crystals, Vorthman and Duvall [19] describe soft-recovery experiments on <100)-oriented crystals shock loaded above the critical shear stress necessary for rapid precursor decay. Postshock analysis of the samples indicate that the dislocation density in recovered samples is not significantly greater than the preshock value. The predicted dislocation density (using precursor-decay analysis) is not observed. It is found, however, that the critical shear stress, above which the precursor amplitude decays rapidly, corresponds to the shear stress required to disturb grown-in dislocations which make up subgrain boundaries. 

The analysis of work-hardening is difficult. Its contribution/, , to the total dislocation resistance / is considerable and increases with strain (Fig. 10.3). 

Analysis of stress distributions in epitaxial layers In-situ characterization of dislocation motion in semiconductors Depth-resolved studies of defects in ion-implanted samples and of interface states in heterojunctions. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

Bridgman had strong views on the importance of empirical research, influenced as little as possible by theory, and this helped him test the influence of numerous variables that lesser mortals failed to heed. He kept clear of quantum mechanics and dislocation theory, for instance. He became deeply ensconced in the philosophy of physics research for instance, he published a famous book on dimensional analysis, and another on the logic of modern physics . When he sought to extrapolate his ideas into the domain of social science, he found himself embroiled in harsh disputes this has happened to a number of eminent scientists, for instance, J.D. Bernal. Walter s book goes into this aspect of Bridgman s life in detail. 

N. Miyazaki, S. Okuyama. Development of finite element computer program for dislocation density analysis of bulk semiconductor single crystals during Czochralski growth. J Cryst Growth 183 S, 1998. 

The use of hexafluoroisopropanol (HFIP) as an SEC eluent has become popular for the analysis of polyesters and polyamides. Conventional PS/DVB-based SEC columns have been widely used for HFIP applications, although the relatively high polarity of HFIP has led to some practical difficulties (1) the SEC calibration curve can exhibit excessive curvature, (2) polydisperse samples can exhibit dislocations or shoulders on the peaks, and (3) low molecular weight resolution can be lost, causing additive/system peaks to coelute with the low molecular weight tail of the polymer distribution... 

The decomposition process can be significantly intensified by the mechanical activation of the material prior to chemical decomposition. Based on a thermodynamic analysis of the system, Akimov and Chernyak [452] showed that the mechanical activation initiates dislocations mostly on the surface of the grains, and that heterogeneities in the surface cause the predominant migration of iron and manganese to the grain boundaries. It is noted that this phenomenon is more pronounced for manganese than it is for iron. 

There are established criteria for obtaining b by using diffraction contrast (23). Briefly, the dislocation intensity (contrast) is mapped in several Bragg reflections (denoted by vector, g) by tilting the crystal to different reflections and determining the dot product of the vectors g and b (called the g b product analysis). 

The main reason for requiring rapid acquisition of different images is for detailed strain analysis. We have seen in Chapter 8 that the Burgers vector of dislocations can be found by noting that there is zero contrast for a screw... 

As shown in the preceding two sections, the constant time version of REDOR, CT-REDOR, may be applied as an expedient alternative to the existing REDOR versions in the presence of strong heteronuclear dipolar couplings. In these cases, only few data points are available for the data analysis, which especially in the case of multiple-spin systems renders an evaluation of the second moments impossible. The efficiency of the dipolar recoupling may be intentionally reduced either via a dislocation of the dephasing Ti-pulses from the centre of the rotor period or via an application of non-Ti-dephasing pulses. A variation of the pulse position fpp... 

To determine the character of the dislocations and the displacement vector b under dynamic reaction conditions, the g A criteria are used. The dislocation contrast is mapped in several reflections (g) by tilting the crystal, including the reflection in which the dislocation is invisible, i.e. = 0 when b is normal to the reflecting planes. Careful analysis (figure 3.25(f) and (g) of defects from the same crystal area (c)) shows that the displacement vector lies in the plane of shear (i.e. parallel to the shear plane), consistent with glide shear, with no lattice collapse. These criteria show the displacement vector to be 6 = (a/7, 0, c/4). 

Figure 3.25. In situ catalysis (a) fresh VPO catalyst (b) dynamic real-time formation of atomic scale catalyst restructuring in butane after 2 min at 400 °C (c) enlarged image of (b) showing two sets of partial dislocations and (d) dynamic image of two sets of extended defects along symmetry-related (201) in (010) VPO after reduction in butane for several hours (diffraction contrast). The inset shows the defect nucleation near the surface. Careful defect analysis shows them to be formed by novel glide shear, (e) One set of the defects in high resolution (f) and (g) show diffraction contrast images of defects in 201 and 201. (After Gai et al, Science, 1995 and 1997 Acta Cryst. B 53 346.)...

---