Plane defects

High resolution image of a region of ZSM-5 ( 010 projection) containing two -defect planes. The explanatory schematic drawing is discussed in the text. 

For y > 0.25, the increase of the vacancy concentration merely leads to a progressive addition of defect planes, i.e. to an increase in the number of tetrahedral layers with respect to the number of octahedral planes. 

Plane defect Plane defect forms a plane that is cleavable because both planes don t match up at the defect location. Imagine a deck of cards where half the deck are sideways. The plane at which the two halves meet is the plane defect. 

Figure 21.31 shows a two-dimensional representation of this kind of line defect. Plane defects are usually seen at the surfaces of crystals or at interfaces between two smaller crystals in a larger piece of solid material, as seen in Figure 21.32. Plane defects can also exist between two different Bravais lattices of the same compound.

The most commonly used methods for evaluation of adhesive bonds are mechanical tests such as tensile shear and peel tests that determine the weakest link in a bonded assembly. Although these tests are useful in the development and quality control of adhesives, they are destructive and cannot offer failure prediction for in-service components. Ultrasonic inspection is the most commonly used non-destructive test method and can accurately assess de bonding in single adhesive bonds, providing that the sensor is perpendicular to the defect plane. However, ultrasound has some limitations in... 

The first system called LiSSA has been developed for interpretation of data from eddy-current inspection of heat exchangers. The data that has to be interpreted consists of a complex impedance signal which can be absolute and/or differential and may be acquired in several frequencies. The interpretation of data is done on the basis of the plot of the signal in the impedance plane the type of defect and/or construction is inferred from the signal shape, the depth from the phase, and the volume is roughly proportional to the signal amplitude. 

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. 

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 ... 

Finally, we can write the signal S( x,y,t) received at time t and for the scanning position (x, y) (the x-axis being in the plane of incidence while the y-axis being normal to it) as an integral over the surface of the defect... 

When plastic deformation occurs, crystallographic planes sHp past each other. SHp is fackitated by the unique atomic stmcture of metals, which consists of an electron cloud surrounding positive nuclei. This stmcture permits shifting of atomic position without separation of atomic planes and resultant fracture. The stress requked to sHp an atomic plane past an adjacent plane is extremely high if the entire plane moves at the same time. Therefore, the plane moves locally, which gives rise to line defects called dislocations. These dislocations explain strain hardening and many other phenomena. 

Etch Profiles. The final profile of a wet etch can be strongly influenced by the crystalline orientation of the semiconductor sample. Many wet etches have different etch rates for various exposed crystal planes. In contrast, several etches are available for specific materials which show Httle dependence on the crystal plane, resulting in a nearly perfect isotropic profile. The different profiles that can be achieved in GaAs etching, as well as InP-based materials, have been discussed (130—132). Similar behavior can be expected for other crystalline semiconductors. It can be important to control the etch profile if a subsequent metallisation step has to pass over the etched step. For reflable metal step coverage it is desirable to have a sloped etched step or at worst a vertical profile. If the profile is re-entrant (concave) then it is possible to have a break in the metal film, causing an open defect. 

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