Defects planar

Anti-MoSj Pt.jB No Trigonal prism Defect planar net... 

Each of these is confined to a site or point, thus, they are called point defects. There are more disl(x ations disturbing the periodicity of lattice sites grain boundaries and surfaces spatially confining the crystal which would have to be infinite if ideal voids and inclusions that are three-dimensional aggregates of point defects of a kind. Depending on their geometries, they are often called line defects, planar defects and volume defects, respectively. 

Crystal imperfections, such as point defects, line defects, planar and volume defects are limiting factors for the applicability of semiconductors in microelectronics. The impact of these defects on band structure, carrier mobility, and optical properties is even found to create principal obstacles for the applicability of certain materials. One example is the II-VI material system for which a prominent obstacle is the creation of extended defects during device operation, connected with the diffusion of doping-related point defects [1], causing lifetime shortening and making the device unreliable. 

PL spectra of the MQWs on planar GaN and LEO GaN are shown as a function of temperature T in Figure 12.13a and b, respectively. The value of the equivalent internal quantum efficiency at 300 K increased with the decrease in the peak energy from 1.1 (V peak) to 29% (B peak) for the MQW on planar-GaN. Corresponding values were 5.3 and 36%, respectively for the MQW on LEO GaN. The fivefold improvement in rfi for V peak is consistent with the decrease in TD and SF densities, which consequently gives rise to the decrease in the nonradiative recombination center concentration [23]. The MQW on LEO GaN exhibited an additional UV peak at 3.24 eV. Remarkably, high r)i t values of B peak being 29% for the MQW on defective planar-GaN and 36% for the MQW on defective areas of LEO GaN surest that B peak... 

N-type nature of ZnO is due to the sensitiveness of ZnO lattice constants to the presence of extended defects (planar dislocations/threading) and structural point defects (interstitials and vacancies) that are commonly found in ZnO resulting in a non-stoichiometric compound. The excess zinc atoms in Zni+dO have the tendency to act as donor interstitials that give its natural N-type conductivity. In ionic form, the excess zinc tends to occupy special Zn interstitial sites with Miller index (1/3, 2/3, 0.875) as shown in fig. 12. These special sites offer passage routes for zinc interstitials to easily migrate within the wurtzite structure [109]. 

The major drawback of this identification method, as used to date, is that only a part of the useful information contained into original Bscan image, i.e. segmented Bscan image, is used for defect characterization. Moreover, it requires the availability of defect classification information (i.e. if the defect is volumetric or planar, e.g. a crack or a lack of fusion), which, generally, may be as difficult to obtain as the defect parameters themselves. Therefore, we... 

Theoretical studies of the interaction between an ultrasonic beam and planar defects have been widely carried out and shown that the upper and lower tip diffraction echoes are characterized by phase inversion. In other words, the measurement of 180° phase shift between these two echoes proves the plane nature of the defect that has generated them. 

Note Conversely, it is important to emphasize that a lack of phase inversion between the signals of two superimposed echoes along the depth axis is not necessarily an evidence that the defect is volumetric (diffraction effect on a planar defect could miss if the geometry of the tips are not favorable). 

Radiography is less effective for detecting arbitrarily oriented planar defects (such as tight cracks or lack of fusion) in thick metal sections unless the likely location and orientation of cracking is known in advance. 

Abstract An Eddy current method applying a High Temperature Superconductor ( HTS ) DC SQUID sensor operating at Uquid nitrogen temperature (77K) is presented. The method is developed for the detection of surface or surface near defects. We compare the performance of the SQUID system with the performance gained from a commercial Eddy current system, while using identical probes. The experimental data are obtained on defects in gas turbine blades. The advantage of planar conformable probes for the use with the SQUID is discussed. 

Several types of Eddy current probes were used with the SQUID system and the commercial system as well. High inductance wire wound probes with a ferritie eore and low induetance planar thick frhn coils were applied. The wire wound probe is the commonly used probe for high resolution conventional testing. The low inductance planar cod is more suited to be apphed in combination with the SQUID system. It is well adapted for surfaee defects and shallow defects. 

Mephisto is devoted to predict the ultrasonic scans (A,B or C-scans) for a priori knowledge of the piece and the defects within. In the present version Mephisto only deals with homogeneous isotropic materials. The piece under test can be planar, cylindrical or have a more complex geometry. The defects can be either planar (one or several facets), or volumetric (spherical voids, side drilled holes, flat or round bottom holes). 

For example, let us consider the case of a planar piece containing a planar defect located near to the surface opposite to the probe (back of the specimen). In such a case, the defect may produce two diffracted echoes arising from the defect tips and supplementary echoes, the so-called comer echoes, that involve two successive reflections one on the... 

We first supposed that the field radiated into the piece by the transducer is known, thanks to the Champ-Sons model. Then, the main approximation used consists in making far field assumptions in the beam defect interaction area. In the case of a focused transducer we assume that the incident wavefronts on the defect are plane. This is equivalent to say that the defect is located in or near the transducer focal area and that a defect located outside this zone does not cause a significant echo. In the case of planar contact transducer, the incident wavefronts on the defect are assumed to be spherical The incident field on the defect is therefore approximated by the product of a spatial function gfp,0,z)describing the amplitude distribution in the beam and a time-delayed waveform < ) ft) representing the plane or spherical propagation in the beam. The incident field on the defect can therefore be approximated for ... 

The methods that are based on the reflection of compression waves will generally not give information about the concrete which lies deeper than the most shallow large planar defect (crack or void ). 

Sampling of checkpoints during the review exercise confirmed some predictable features, notably that radiography would miss planar defects such as lack of side wall fusion, and that ultrasonic operators tended not to report undercut, porosity or the smaller slag inclusions. 

Poly(vinyl fluoride) [24981-14-4] (PVF) is a semicrystaltiae polymer with a planar, zig-zag configuration (50). The degree of crystallinity can vary significantly from 20—60% (51) and is thought to be primarily a function of defect stmctures. Wide-line nmr and x-ray diffraction studies show the unit cell to contain two monomer units and have the dimensions of a = 0.857 nm, b = 0.495 nm, and c = 0.252 nm (52). Similarity to the phase I crystal form of poly (vinytidene fluoride) suggests an orthorhombic crystal (53). 

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