Pinhole structures

To fully integrate the confocal concept with portable, stand-alone micro-/nanodevices, inexpensive yet functionally equivalent miniature microscopes are required. Diode lasers, microlenses, pinhole structures, and PMT detectors must be reliably fabricated then aligned... 

Ni-YSZ cermets deposited by RF sputtering (230 nm) were found to have micro-structural features consisting of columnar grains 13 to 75 nm long and 9 to 22 nm wide, and showed good adhesion to the YSZ layer on which they were deposited [128], In a three-layer Ni-YSZ-Ni film deposited on NiO by RF sputtering in another study, the YSZ layer exhibited a columnar structure with some pinholes [129], Microstructural and electrochemical features of Pt electrodes patterned by lithography on YSZ have also been studied [130,131]. 

The pinhole density of polyimide was assessed by a statistical evaluation of shorts using an TiWAu - polyimide - TlWAu multilevel structure where each die contained 3275 crossovers of first and second metal. The probability of good crossovers was taken as... 

Pinhole density is another property of interest in defining insulation integrity. It was indirectly assessed from the number of shorts in a statistical number of probed die where the die was a multilevel test structure consisting of TiWAu-polyimide-TlWAu with 3275 crossovers of first and second metal per die. The results indicated that the probability of a short in a crossover for 1.2 y thick PI2545 was 1 in 133,333. 

CuInSi (and, even more, CuInSei) are strong candidates for thin-film photovoltaic cells. For this purpose, the chalcopyrite structure (which is an ordered lattice) is preferred over the disordered, zincblende form. Due to the large absorption coefficients of these materials, a 1-iJim-thick film is more than enough to absorb almost all the suprabandgap radiation. Somewhat thicker films are generally used, due to problems of pinholes, which commonly occur in thinner films. A number of methods have been used to deposit these films. Surprisingly, very few (published) attempts have been made to deposit them by CD. 

Even closer to cell membranes than monolayers and bilayers are organized surfactant structures called black lipid membranes (BLMs). Their formation is very much like that of an ordinary soap bubble, except that different phases are involved. In a bubble, a thin film of water — stabilized by surfactants — separates two air masses. In BLMs an organic solution of lipid forms a thin film between two portions of aqueous solution. As the film drains and thins, it first shows interference colors but eventually appears black when it reaches bilayer thickness. The actual thickness of the BLM can be monitored optically as a function of experimental conditions. Since these films are relatively unstable, they are generally small in area and may be formed by simply brushing the lipid solution across a pinhole in a partition separating two portions of aqueous solution. 

Fig. 11.1. This figure illustrates the process of selection not by restriction but by fit into the next hierarchy of structures. The suitability is a purely chemical phenomenon and the pinhole plate is an imperfect symbol of fit of fragments into the structures of nucleotides which, in turn, are swept up by polymerization reactions. The aperture at the next station restricts on the basis of suitability of nucleic acids for the development of catalytic units. The aperture symbolizing that differentiating process is larger because there are many ways for nucleic acids to end up in living systems in contrast to the first aperture in barrier 1 that is restrictive to the point that only nucleic acids can cross that threshold. The third aperture is the largest yet because there are many ways to make a living. It is movable because the living units that appear will be sensitive to environmental conditions that can mean failure to life forms which would be quite suitable to exist under different conditions.

The barrier quality is determined by the surface properties of the polymer substrate and the properties of the metal layer [12]. The most crucial factor is the surface quality of the substrate. If there is an adsorbate on the surface, it may be desorbed during the evaporation process, which leads to pinholes and poor adhesion of the metal layer. If the adsorbate is water, A1 may react with the water and lead to the formation of A1 oxide which has barrier properties substantially inferior to those of metallic Al. Also the lack of functional groups on the polymer surface causes poor adhesion and thus a change in the structure of the layer. 

However, SAMs are rarely structurally perfect and typically contain defects where crystalline domains meet, at step-edges, and where the electrode is not coated with the SAM. Defects of this kind all facilitate mass transport to the electrode surface where efficient electron transfer can take place. A key objective in characterizing SAMs is to map out the nature, size and distribution of the pinholes and other defects. Undoubtedly, scanning probe microscopy, such as the AFM and STM techniques discussed earlier in Chapter 3, play important roles in this area. However, voltammetry is an extremely powerful approach for detecting defects in SAMs when in contact with solution. This extraordinary sensitivity arises from the ability to routinely detect currents at the nanoamp and picoamp levels which... 

X-ray scatter imaging can be performed in principle with such components as lenses and mirrors, though these suffer from poor efficiency beyond the soft X-ray region. In practice, X-rays having the penetrability (E0 > 40 keV) needed for explosives XDI can be collimated only by arrangements of pinholes, slits, etc. in otherwise absorbing structures. The collimation scheme to be used in a certain situation for XDI depends... 

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