Pinhole defect

SFM image of oxidized Si wafer showing pinhole defects 20 A deep. 

To avoid penetration and filament formation via static and randomly scattered pinholes, one approach is to diminish the area of the junction until statistically the presence of a pinhole defect is near vanishing, as might be calculated by a Poisson distribution. An example of this strategy is the use of a nanopore junction of 50 nm diameter, though in this case the device fabrication yields were still reported to be quite low, down to a few percent [16]. 

The primary disadvantages of metals relate to their cost and quality control. Metals are inherently more expensive to purchase and to fabricate into a useful container. Metals also are prone to the development of pinhole defects during manufacturing that can drastically compromise their barrier properties— especially in particularly thin sections. Not only can these defects be deleterious to the container, but they can also compromise the quality of the pharmaceutical itself. Drug product should be monitored to assure that no metallic packaging defects have been transferred to the preparation—especially in ophthalmic drug products. Much like copolymerization of plastics, metals can be alloyed to enhance their characteristics as The USP has no test requirements for... 

Time dependencies measured in Ref. 26 showed that the adsorption of lipid at the ITIES is fully reversible. The lipid adsorption on and desorption from the ITIES occur at about the same time scale. The monolayer self-assembled at the ITIES is in dynamic equilibrium with dissolved lipid molecules that allows any pinhole defects to be healed. In contrast, self-assembly on the solid/liquid interface often involves irreversible adsorption and requires high purity of chemicals, complex pretreatment, and preparation protocols to obtain a low-defect-density molecular monolayer (32). 

FIGURE 12. Large-area image of a dodecanethiol monolayer on Au(lll) showing domains and pinhole defects. Reprinted with permission from Reference 185. Copyright (1995) American Chemical Society... 

Other investigators reported pinhole defect density data that scale roughly with the inverse of the square of the film thickness, which can be derived from dynamic arguments, as was shown in Eq. (11.20). Spinodal decomposition dominates the nucleation process under clean room conditions, while particle nuclea-tion increases in higher aerosol concentration environments. ... 

For reference, silane-based monolayers prepared on flat wafers and other non-porous substrates have been reported to have a population density of 4.8 silanes/nm [14]. Thus, the toluene preparation of thiols SAMMS seems to provide reasonably good surface coverage of the internal pore surfaces of the mesoporous silica, but there are certainly defects (e.g. pinhole defects and dangling hydroxyls) in the monolayer structure, leaving the question, Is the level of coverage limited by the pore curvature, or is it due to the procedure employed . As we shall see, it is due to the procedure. 

In the past, thin metal membranes have been fabricated by rolling between precision rollers, but potential for pinhole defects limits this method for Pd-alloy membranes to a current state of the art of 25 p,m (0.001 in.). Difficulty in controlling... 

The initial alloy coatings deposited on to polymers showed a tendency to exhibit pinhole defects most of which have since been attributed to the presence of dust particles. Polymer films have a propensity to accumulate an electrostatic charge that attracts fine particles. As an alternative, interim method to address the issue of defects in the Pd-Cu alloy membrane films, films were deposited onto smooth, silicon wafers. Particulate and other contaminants can be more readily controlled (i.e., minimized) on a silicon surface, in comparison to plastic, and is considerably smoother than plastic. In experiments using magnetron sputtering, we were able to produce defect-free Pd-Cu films on 12 in. diameter silicon and 4 in. square glass plates. A released film, 4 p.m thick, is shown in Fig. 11.4. Films as thin as 0.7 p.m have been produced in this way. 

No polymeric material forms an impervious barrier to gas or vapor molecules. The transmission of such molecules through a membrane is a result of intermolccular spaces, pinhole defects, or porosity, or some combination of these three structural features of the material. In this chapter we are restricting the term permeation to the movement of gas or vapour molecules through molecular scale voids. The quantity of permeant is usually measured as the volume at STP for a gas, or the mass in the case of a vapor. 

Defects Pinhole defects and cracks allow the passage of N2. These pinhole defects cause the efficiency of the membrane to separate O2 to fall significantly. The processing must be optimized to avoid the formation of these defects. 

In January 1993, when SG was put in service for the first time, after 70 hours of operation, a water leak took place due to a linear pinhole defect in the end cap of one of the orifice assemblies at SG inlet. All similar end caps were ultrasonically inspected and four more were found to have similar defects. The leaking cap was replaced and additional covers were welded for defective caps. The failure was attributed to material defect. 

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