Crystalline orientation

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. 

MW and MWD are very significant parameters in determining the end use performance of polymers. However, difficulty arises in ascertaining the structural properties relationship, especially for the crystalline polymers, due to the interdependent variables, i.e., crystallinity, orientation, crystal structure, processing conditions, etc., which are influenced by MW and MWD of the material. The presence of chain branches and their distribution in PE cause further complications in establishing this correlation. 

Amorphous orientation average Crystalline orientation average Nuclear spin number Scattered intensity Scattered intensity Transmitted intensity... 

The run-to-run deposition zone temperature (350-425 °C) was the first parameter varied. Temperature variation affected film stoichiometry [Fig. 6.25(a)] and crystalline orientation [Fig. 6.25(b)], while not significantly affecting the deposition rate [Fig. 6.25(c)], From Fig. 6.25(a), we can see that the films were closest to stoichiometry when deposited at 395 °C. Cu-to-In ratios ranged from... 

Figure 6.25. Deposition temperature versus (a) elemental composition, (b) crystalline orientation, and (c) deposition rate for CuInS2 films with precursor feed rate of 1.6 g/h. In plot (a), the accuracy limit of 5% per element resulted in an anomalous overall percent composition for the In-rich, S-poor deposited material.

Surface lattice structure Density of active surface atoms and reactivity of the surface determined by the crystalline orientation of silicon/electrolyte interface... 

Figure 24. Schematic illustrations of the conditions of surface lattice structure (a) amorphous-like surface with no identity of orientation, (b) surface with kinks, steps and terraces characteristic of certain crystalline orientation and (c) surface with no identity of the lattice structure of the crystal due to the coverage of an amorphous oxide film. 

The morphology may be quite complex with consideration of perfectness of crystallinity, orientation of molecules within amorphous regions and tie molecules. 

Kim, J. C Cakmak, M. and Zhou, X Effect of composition on crystalline orientation and optical properties of biaxially stretched PEN/PEI films, in Proceedings of the 55th SPE ANTEC 97 Conference, May 5-8, 1997, Toronto, ON, Canada, Society of Plastics Engineers, Brookfield, CT, 1997, Vol. 2, pp. 1588-1592. 

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. 

Diffusion and permeability are inversely related to the density, degree of crystallinity, orientation, filler concentration, and cross-link density of a polymeric film. Generally, the presence of smaller molecules, such as plasticizers, increases the rate of diffusion in polymers since they are more mobile and can create holes or vacancies within the polymer. The rate of diffusion or permeability is fairly independent of polymer chain length just as long as the polymer has a moderately high chain length. 

To a flask containing 20 gm (0.08 mole) of methylenebis(4-phenyl isocyanate) in 150 ml of xylene is added 0.03 gm of l-ethyl-3-methyl-3-phospholine-l-oxide catalyst. The solution is refluxed for 4 hr, during which time carbon dioxide is being evolved. The xylene solvent is removed under reduced pressure to afford a nearly quantitative yield of the solid polycarbodiimide. The latter polymer was pressed at 250°C to afford a clear, crystalline, orientable film with a tenacity of about 50,000 psi, an initial modulus of 410,000 psi, and a 20 % elongation at 25°C. 

Optical Microscopy. The reflectance of an anisotropic surface in normal incidence depends on die degree of polarization of the light and the crystalline orientation of the surface in relation to the light vibrations. In polarized light and in the case of an opaque birefracdve crystal, whose absorption coefficients... 

Crystallinity - Orientation of disordered long chain molecules of a polymer into repeating patterns. Degree of crystallinity affects stiffness, hardness, low temperature flexibility and heat resistance. Crystallinity can make some linings still and boardy, difficult to lay. 

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